Yarway Industrial Steam Trapping Handbook Guide

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Yarway Industrial Steam Trapping Handbook Guide | Manualzz
The leading name in steam traps.
Yarway Steam Traps
The Industrial Steam Trapping Handbook.
Yarway Industrial Steam Trapping Handbook
Contents
All steam traps and related equipment is governed by an applicable code of construction. ASME,
DIN, B 31.1 and others are mandated by law and code. The end user must use the applicable code
when designing, constructing or repairing any steam related equipment. This guide book is to be
used as a basic guide and does not address the required Codes for any region. The end user is
responsible to ensure all applicable codes are followed as required in each jurisdiction.
Contents
Chapter 1Steam trapping, an overview����������������������������������������������������������������������������������������3
Chapter 2Basics of steam and steam systems���������������������������������������������������������������������������7
Chapter 3Operating principles of steam traps��������������������������������������������������������������������������14
Chapter 4Principles of steam trap application�������������������������������������������������������������������������27
Chapter 5Principles of steam trap installation�������������������������������������������������������������������������39
Chapter 6Steam trap maintenance and troubleshooting���������������������������������������������������������44
Chapter 7
Condensate return systems���������������������������������������������������������������������������������������55
Appendix A
How to trap process equipment��������������������������������������������������������������������������������65
Appendix BSteam trap evaluation methods���������������������������������������������������������������������������������77
Appendix CGlossary of terms��������������������������������������������������������������������������������������������������������84
Appendix DUseful tables���������������������������������������������������������������������������������������������������������������86
Copyright © 2017 Emerson. All rights reserved. No part of this publication may be reproduced or distributed in
any form or by any means, or stored in a database or retrieval system, without t written permission. Emerson
(PVC) provides the information herein in good faith but makes no representation as to its comprehensiveness
or accuracy. Individuals using this information in this publication must exercise their independent judgment in
evaluating product selection and determining product appropriateness for their particular purpose and system
requirements. PVC makes no representations or warranties, either express or implied, including without
limitation any warranties of merchantability or fitness for a particular purpose with respect to the information
set forth herein or the product(s) to which the information refers. Accordingly, PVC will not be responsible
for damages (of any kind or nature, including incidental, direct, indirect, or consequential damages) resulting
from the use of or reliance upon this information. Emerson reserves the right to change product designs
and specifications without notice. All registered trademarks are the property of their respective owners.
Printed in the USA.
2
Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
Chapter 1 – Introduction
Steam traps are used wherever steam is
used and they are control valves. Their basic
function is to allow condensate to flow, while
preventing the passage of steam until it has
given up its heat by condensing back to water.
There are literally millions of steam traps in
use worldwide.
Steam trap users range from laundries and
tailor shops (with a few traps) to huge refineries
and chemical complexes (with 10,000 to
15,000 units). Paper mills, textile plants, steel
mills and food processors are all large users
of steam and steam traps. Colleges, hospitals,
prisons, government agencies, and similar
large building complexes with central steam
heating systems are also users of steam traps.
This wide range of users creates an equally
wide range of steam trap applications. In turn
this wide variety of applications is matched by
a seemingly bewildering array of steam trap
types and sizes.
Energy costs lead to new awareness because
of costs and environmental requirements
In recent years, user interest in steam traps
has closely paralleled the increases in
energy costs. This interest has been born of
necessity. The high fuel costs associated with
malfunctioning traps, and the low level of
attention generally paid to their proper use,
have simply become economically too painful to
ignore. The malfunctioning traps waste energy,
which in turn increases the requirement
to produce steam and may contribute to
environmental issues.
A few of the larger and more sophisticated
trap users have developed test and evaluation
programs to determine the kinds of traps
that perform best in their plants. They
have experimented with various types from
different manufacturers. Organizational
changes have created the job of Energy
Conservation Officer, and his function invariably
has led him to study the subject of steam
traps. As a result, the skills necessary for
diagnosing inefficient steam systems, and
prescribing appropriate cures, have improved.
Figure 1.1
Figure 1.1 shows an ultrasonic steam leak
detector and an infrared heat loss sensor.
Both are used increasingly in efforts to detect
energy losses. Identifying malfunctioning and
misapplied steam traps is now recognized
not only as an important task, but also one
of greater complexity than initially perceived.
Services of consultants and service companies
specializing in the proper maintenance of
steam traps have become increasingly popular.
No universal steam trap
With all of this attention and inquiry, many
users have become aware that there is no
universal trap or single trapping technology for
all their needs. Appreciation has developed for
the fact that many criteria must be considered
in selecting a steam trap for a particular
application. Different trap types will be selected
or preferred according to the importance a user
assigns to various criteria.
The objective of this book is to provide an
up-to-date reference for trap users whose
requirements may range widely. Its intent
is to clarify and simplify the basics relating
to steam trap selection, sizing, installation
and maintenance without ignoring the
subtleties and nuances of interest to the
more knowledgeable reader.
While all steam traps have the same basic
objective, pass condensate but trap steam,
(they are also expected to pass air and other
noncondensible gases without loss of steam),
there is a wide range of design approaches to
achieving this objective. Traps come in a variety
of shapes and sizes. Some weigh less than a
pound while others will exceed two hundred
pounds. Some are intended for small copper
tubing while others will be used with three inch
steel pipe. Some may be used at pressures
exceeding 2,500 psi while others may actually
see vacuum service. Some are designed to
drain several pounds of condensate an hour
while others are expected to pass tens of
thousands of pounds of condensate an hour.
TE 600
Software
Photo shows system manufactured by Miyawaki
that combines testing of the trap with data
storage and reporting. See VCTDS-03240.
3
Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
Trap preferences vary
While steam is the same around the world,
there are interesting preferences for one type
of trap over another in different countries.
This tends to reinforce the conclusion
that despite the universality of the laws of
thermodynamics, the problem of selecting
a correct steam trap has no single correct
answer. All major industrial countries have
their own steam trap manufacturers serving
local markets. Increasingly, they are trying to
export their more successful models. This has
had the beneficial result of increasing user
options. It also has increased the user’s need
to understand fully the limitations and the
benefits of those options. Emerson is a global
supplier for steam traps, many other types
and vendors are available for similar duty and
services. The references in this book include
Emerson products and other similar brands for
illustration purposes.
Trap selection criteria
Steam traps are analogous to motor vehicles
in that each has a single underlying purpose
but is available in a wide variety of models and
options. Selecting the correct model depends
on user needs and preferences. In selecting
the right trap a user must think hard about
the priority of his needs. While efficiency and
reliability may seem obvious requirements,
other criteria (such as responsiveness to
changing pressures and condensate flow rates,
installation flexibility, ease of maintenance
and troubleshooting) are more judgmental.
Nevertheless, they can significantly reduce the
costs of operating an efficient steam system.
Increasingly, users are recognizing all steam
traps have the same objective: pass condensate
but trap steam the difference between
purchased cost, installed cost, and life-cycle
cost. When all of these issues are considered,
steam trap selection becomes a matter
requiring thoughtful evaluation. At the least, a
wrong selection means a savings opportunity
missed; – at the worst, it can mean a costly
disruption of production.
Cost considerations
Steam traps, like all other pieces of mechanical
equipment, will fail in time. They may fail
closed thereby restricting flow, or they may
fail open, freely passing steam. It is difficult
to appreciate fully the cost consequences of
malfunctioning steam traps in a large plant
without going through some basic arithmetic.
Consider a plant with 6,000 traps and a
consrvative assumption that at least 10% have
failed in the open position and are "blowing
through," wasting steam. Six hundred traps,
losing 20 pounds of steam per hour per unit,
for twenty-four hours, are losing 288 thousand
pounds of steam per day. While steam
generating costs vary from plant to plant (and
are revised annually) an estimate of $5.00 per
thousand pounds is very conservative. In this
example, that equals $1,440 per day for a rate
of $525,600 per year.
• 6,000 traps x 10% = 600 failed traps
• 600 failed traps x 20 lb/hr x 24 hr/day =
288,000 lb/day
• 288,000 lb/day x $5.00/1,000 lb = $1,440/day
• $1,440/day x 365 day/year = $525,600/year
These are all conservative numbers.
Figure 1.2
All steam traps have the same objective: pass condensate but trap steam
Water
Steam
4
Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
The costs resulting from traps that have failed
in the closed position are not considered in
the preceding example. They are much more
difficult to quantify but they are no less real.
These costs result from reduced productivity or
product quality and higher rates of equipment
damage due to corrosion, water hammer or
freeze ups.
Why would any plant manager allow his steam
YARWAY MODEL 741traps to waste this amount
of steam? The answer is that he probably
doesn't really know it is happening. If each
failed trap had high visibility, it would be a
different story. But with traps discharging into a
closed return system the same telltale plumes
of vapor, that quickly identify the leaking
valve packing or flanged joint, are missing.
Because frequently they fail to create a clearly
visible problem, traps simply don't receive
the attention they deserve. This example does
not include any calculation to the amount of
pollution generated during the production of the
steam in the first place. A good review of the
pay back process will include environmental
issues as well as the direct cost of steam.
Process and protection traps
Industrial steam traps can be divided into two
major groups: (1) traps designed for draining
process equipment such as tire presses, drying
rolls, air heaters and heat exchangers (often
referred to as process traps); (2) traps designed
for draining steam mains or tracing systems.
The latter serve a protection function and are
sometimes referred to as protection traps.
Protection service, such as steam main drips
and tracer heating, is by a wide margin the
most common trap application and makes up
the majority of the 6,000 units referred to in the
earlier example. They generally see very light
condensate loads, often less than 50 pounds
per hour. Process traps are generally designed
for condensate loads of several hundred
pounds per hour to several thousand pounds
per hour.
Yarway Model 741
5
Yarway Industrial steam trapping handbook
Chapter 1 - Steam trapping, an overview
Summary
Frequently underestimated as a significant
contributor to efficient plant operation,
steam traps are increasingly recognized as
a small piece of equipment with a large role
in optimizing plant efficiency and reduced
environmental costs.
Designed to release condensate and air from
steam systems without allowing the passage
of steam, they are a small automatic selfactuated valve. They come in a wide range of
sizes and models because they must meet a
wide range of pressures and condensate load
conditions. Users also tend to have different
preferences for the kind of performance they
expect from a trap.
Steam traps that have failed in service
are seldom highly visible unless they are
discharging directly to the atmosphere.
Because of this, they generally receive
inadequate maintenance attention. The direct
cost consequences of this inattention, when
measured in terms of unnecessary fuel
consumption, can be startlingly high.
The indirect cost consequences, in terms of
lost production or damaged equipment, can
also be significant although they are less
easily quantified and frequently not properly
assigned to a faulty steam trap installation.
Any successful effort to control these costs
must be based on a solid foundation of
certain basic factual information about steam,
condensate, how steam traps work, and the
requirements of the systems into which they
are installed.
Figure 1.3
Typical process trap application
Steam in
Hot process
fluid
Trap
Cool process
fluid
Condensate out
Figure 1.4
Yarway drip traps protect equipment and piping against damage that can result if condensate
is not drained
Steam from boiler
Trap
Trap
Trap
Turbo generator
6
Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
Chapter 2 – Introduction
Generating steam is not an end in itself.
Steam is generated as a convenient way of
transferring energy (heat and pressure) from
one place to another. Its uses can be for
heating, drying, cooking, curing or spinning
a turbine – to name a few. It is the special
properties of steam and water, and their easy
availability, that make them so widely selected
for this energy transferring role.
A review of some fundamentals concerning
steam and condensate can be helpful. When
water is heated, its temperature continues to
rise up to the boiling point. Continued heating
does not raise the temperature of the water
but causes it to boil into steam having the
same temperature as the liquid.
If water is heated in a closed vessel, the
reaction is different in an important way.
Once boiling starts and with the heating
continued, several things occur; the pressure
in the vessel increases and the temperature of
both the water and the steam also increases.
This means that water has a new and
higher boiling point as pressures increase.
For instance, at 100 psi water boils at 338°F
instead of the familiar 212°F at atmospheric
pressure. If heating continues after all the
water has been evaporated, the temperature
and pressure of the steam continues to
increase and the steam is then called
superheated steam.
If the heating is discontinued, a process is
started that is just the reverse of that described
above. As the vessel cools, the pressure also
decreases. Initially, no condensation takes
place as the steam gives up that portion of the
heat it acquired after all the water in the vessel
evaporated. After all the total heat of steam at
atmospheric pressure the superheat has been
given up, however, water starts to condense
on the vessel walls. Continued cooling results
in a decreasing pressure and the formation
of more condensate. Ultimately all the steam
will condense into water and the temperature
and pressure will return to that which existed
before the heating process started.
Figure 2.1
Steam and condensate system
Steam main
Air
heater
Trap
High
pressure
steam
Heat
exchanger
Trap
Boiler
Jacketed
kettle
Trap
End of
main trap
Tracer traps
Drip
trap
Condensate return
Flash tank
7
Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
{
Figure 2.2
Total heat of steam at atmospheric pressure
Total heat
of steam
(1150 BTU)
1 pound water
evaporated
into steam at
atmospheric
pressure
Latent heat of
vaporization
970 BTU
Sensible heat
of water
180 BTU
A more realistic situation is that of a steam
generator or boiler with its heat and pressure
energy being transferred by a piping system to
equipment that is performing a useful task. As
the steam gives up its heat in the equipment,
condensate is formed. The condensate can then
return to the boiler for reheating and the cycle
is repeated. Figure 2.1 shows such a system.
Basic definitions
Some basic definitions are really essential to
a full understanding of the steam generating
cycle and the proper use of steam traps in an
efficient steam-using system:
• British thermal unit (BTU): the quantity of
heat required to raise one pound of water
1 degree Fahrenheit.
• Sensible heat: heat that produces a
temperature rise in a body such as water.
• Latent heat of vaporization: heat that
produces a change of state without a change
in temperature, such as changing water
into steam.
• Saturated steam or dry saturated steam:
steam at the temperature of the water from
which it was evaporated.
• Wet steam: typically, steam is not dry but
contains fine water droplets resulting from
the boiling process. The significance is that
wet steam has a lower heat content than
dry saturated steam.
{
{
Heat required to convert
1 pound of water at 211°F to
1 pound of steam at 212°F
Heat required to raise 1 pound
of water from 32°F to 212°F
• Saturated water: water at the same
temperature as the steam with which it is
in contact.
• Superheat: heat added to dry saturated
steam.
Additional concepts
• Total heat of steam: the total BTU content
of steam, including sensible heat of water,
latent heat of vaporization and superheat
(if any).
This concept is shown in Figure 2.2 for
steam at atmospheric pressure.
The conclusion that can be drawn from
Figure 2.2 is that there is more than five
times the heat in one pound of steam at
212°F than in one pound of water at the same
temperature. This means that for efficient
heating with steam, condensate must be
removed quickly. The presence of condensate
acts to reduce the surface area exposed
to steam with its much greater BTU (heat)
content.
The total heat of saturated steam at any
pressure is the sum of latent and sensible
heat and is shown in Figure 2.3.
Higher pressures mean higher temperatures
and faster heat transfer. But it is worth noting
that higher pressures mean less latent heat
of steam. More steam must be condensed at
higher pressures, to transfer a given number
of BTUs, than is the case at lower pressures.
8
Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
• Discharge temperature of steam traps:
The temperature of discharging condensate
measured at the steam trap’s inlet. Also,
sometimes referred to as the temperature
at which a steam trap starts to open.
• The saturation curve: graphic representation
of the pressure and temperature at which
saturated steam and water exist.
As pressures increase in a boiler, so does the
boiling point of water. Figure 2.4 shows how
the boiling point increases from 212°F at 0 psi
to 489°F at 600 psi. This curve is called the
Saturation Curve. At temperatures above the
curve, steam is in a superheated condition.
At temperatures along the curve both
steam and condensate are in the saturated
condition. At temperatures below the curve,
condensate is in the subcooled condition; i.e.
its temperature is below that of saturated
steam and water at that pressure.
Understanding the physical phenomena
represented by the saturation curve is essential
to understanding why in certain applications
some types of steam traps are preferred
over others. Most steam traps are unable to
perform well over the entire range of pressure
and temperature conditions represented in
Figure 2.4. For example, some traps will work
well at higher pressures but will be unable to
shut-off the flow of steam at lower pressures.
Figure 2.3
Total heat of steam at pressures of 0 to 100 psi
Total heat of steam
(L and S)
1200
Alternatively, some that shut-off steam at
lower pressures are unable to open sufficiently
to allow a full flow of condensate at higher
pressures. Also, many applications require
a steam trap that will discharge condensate
very quickly after it forms to obtain maximum
heating efficiency for the equipment it is
serving. This condensate will be very close to
steam temperature perhaps only 3 or 4 degrees
below that of steam. In other applications, the
heat in the condensate as well as the heat
in the steam can be used. In these cases the
steam trap is not expected to open until the
condensate is 30 or 40 degrees below that
of steam.
Steam traps that open and close at
temperatures just a few degrees below steam
temperature are often referred to as 'hot' traps.
Those that discharge condensate significantly
subcooled below steam temperature are called
'cool' traps, even though they may be operating
at temperatures much higher than 212°F. The
requirements of the application determine
which type of trap is most suitable.
1100
1000
BTUs per pound of steam
900
Latent heat (L) available
at various pressures
800
700
600
500
400
Sensible heat (S) available
at various pressures
300
200
Sensible heat at
atmospheric pressures
100
0
10
20
30
40
50
60
70
80
90
100
Figure 2.4
Saturation curve
500
Area of superheated steam
400
Boiling point of water
(temperature of saturated
steam and saturated water
at various pressures
300
Area of subcooled water or condensate
200
0
100
200
300
400
500
600
9
Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
Figure 2.5 shows graphically the concepts
described above. One type of trap (represented
by the Trap A curve) opens quickly to discharge
condensate when its temperature has dropped
only a few degrees below that of steam. Its
discharge temperature is said to parallel the
saturation curve because it opens to discharge
condensate the same few degrees below
steam temperature over a wide range of
steam pressures.
In contrast, the number of degrees that
condensate must cool below steam
temperature before a different type of trap
(represented by the Trap B curve) will open,
varies significantly at different pressures. In
this example, condensate must cool a relatively
large number of degrees below that of steam
before it will open at pressures above 300 psi.
As steam pressures drop below 300 psi, the
number of degrees condensate must cool
before the trap will open is progressively
reduced until at 25 psi the trap is open
continuously (unable to close), discharging
both steam and condensate.
• Steam tables: listings of the heat content
of steam in BTUs and its volume in ft3·lb at
various pressures and temperatures.
The properties of saturated steam are most
frequently summarized in steam tables,
some of which are very extensive. Figure 2.6
shows this form in a very abbreviated listing.
Appendix D provides more complete but still
abbreviated tables.
Steam tables are essential for calculating
the amount of steam to do a certain heating
job. When the amount of steam required is
known, so is the amount of condensate that
will be produced and, in turn, the size of
steam trap that is required. Chapter 4, Steam
trap application, discusses in greater detail
the calculations necessary in estimating
condensate loads.
Flash steam: steam that results when
saturated water or condensate is discharged
to a lower pressure. When saturated water or
condensate is released to a lower pressure, its
boiling point is instantaneously reduced. Some
of the condensate will boil or flash into steam.
This is steam that could not exist at the higher
pressure.
Figure 2.5
Discharge temperature characteristics of two different types of steam traps
500
Saturation curve
(Boiling point of water
at various pressures)
Temperature °F
400
300
Trap A
Discharge temperature of a steam trap
that can parallel the saturation curve
200
100
0
Trap B
Discharge temperature of a steam trap that is unable to
parallel the saturation curve. Note that in this example,
this trap will be unable to close at pressures below 25 psi
100
200
300
400
500
600
Pressure, psig
10
Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
While the brief explanation of flash steam
given above is accurate, the significance of the
subject for both steam systems and steam
trapping justifies more discussion. Here are
several practical reasons for this:
1.The individual that expects to know the
difference between a trap that is operating
properly and one that is not must know the
difference between flash steam and live
steam.
2. Flash steam created unexpectedly in
a poorly planned steam system can
significantly reduce the efficiency of
that system. It can also (under extreme
conditions) cause malfunction of certain
types of steam traps.
3. Flash steam in a properly designed steam
system is an important element in using
steam efficiently at successively reduced
pressures for a series of different jobs.
By way of example, consider a steam trap
draining a piece of equipment operating
at 100 psi. Steam flows to the equipment
and condenses as it gives up its heat. It is
then that the steam trap should open, to
drain the condensate, and reclose before
live steam escapes. But the temperature of
condensate at 100 psi is 338°F and, if it drains
directly to atmospheric pressure, the laws
of thermodynamics require it to achieve its
atmospheric boiling point instantly and become
212°F. This is accomplished by some of the
condensate flashing into steam also at 212°F.
This discharge from the outlet of the trap then
is a combination of hot condensate and flash
steam and is typical of a properly functioning
steam trap.
Flash steam problems
Confusion over flash steam starts with an
individual, who is looking at a trap that is
discharging to atmosphere, and who then
attempts to decide if the steam coming from
that trap is really live steam that has leaked
through (a faulty trap) or if it is flash steam, the
normal result of hot condensate boiling upon
release to a lower pressure (a healthy trap).
Both experience and judgment are needed
to make a correct assessment. Chapter 6,
Steam trap maintenance and troubleshooting,
discusses this problem more fully.
Flash steam can create problems in the
piping systems used to return condensate to
the boiler. Condensate return systems that
have not been properly designed to accept the
volume of flash steam they actually experience
will perform poorly. Flash steam expands to
many times the volume that it had as water.
Saturated water at 15 psi will have about
1600 times the volume when it flashes to steam
at atmospheric pressure. This expansion
process can so pressurize condensate return
systems that proper drainage of the steam
heated equipment, and performance of certain
types of steam traps, are impaired. Connecting
additional equipment to an already existing
condensate return system is frequently the
cause of excessive back pressures.
Figure 2.6
Steam table (see Appendix C for expanded table)
Heat in BTUs per lb
Pressure
psig
0
25
50
100
200
300
400
600
Temperature
°F
212
267
298
338
388
422
448
489
Sensible
180
236
267
309
362
399
428
475
Latent
970
934
912
881
837
805
776
728
Total
1150
1170
1179
1190
1199
1204
1204
1203
Specific volume of
saturated vapor
ft3·lb
27.0
10.5
6.7
3.9
2.1
1.5
1.1
0.75
11
Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
Flash steam as a valuable resource
Flash steam in a properly designed cascading
return system allows for the efficient use of
steam doing several different heating tasks
at successively reduced steam pressures.
Table (Figure 2.7) shows the percent of flash
steam formed when condensate is discharged
from a higher to lower pressure. For example,
7% of condensate discharged from a 100 psi
system to a 30 psi system will be converted to
flash steam. Tables such as these are used
in designing condensate return tanks and
systems.
Factors affecting steam systems
Up to this point emphasis has been focused
on matters relating to the heat content of
steam and water. However, there are some
additional considerations associated with
steam systems that have special significance
for the steam trap user and designer alike.
While these are common problems, their
adverse effects can be minimized by good
planning and equipment selection. These
problems include:
• Water hammer: condensate will always
collect in the low points of a steam system
unless special effort is made to drain it away
or to eliminate the low point. Figure 2.8
shows a sagging steam main that has
allowed condensate to accumulate.
Steam flowing in the main, often at
surprisingly high speeds (90 miles per
hour is not unusual), will pick up slugs of
condensate and slam them into valves,
elbows, steam traps or other such equipment
with devastating affect. Steam trap designers
seek to create robust products that will
withstand water hammer. Steam trap users
are best advised to correct water hammer at
its source by following good piping practice.
Figure 2.7
Percent of flash steam formed
Initial steam
pressure
psig
25
50
75
100
125
150
175
200
225
250
300
350
400
450
500
550
600
Sat.
temperature
°F
267
298
320
338
353
366
377
388
397
406
422
436
448
459
470
480
489
Flash-tank pressure*, psig
0
5.7
9.0
11.3
13.3
14.8
16.8
17.4
18.7
19.7
20.7
22.4
24.0
25.5
26.8
28.2
29.2
30.2
5
4.1
7.4
10.8
11.7
13.4
14.8
16.0
17.5
18.2
19.2
21.0
22.7
24.2
25.3
26.7
27.8
28.8
10
3.0
6.2
8.6
10.6
12.2
13.7
15.0
16.2
17.0
18.2
20.0
21.6
23.0
24.4
25.7
27.0
28.0
20
1.0
4.3
6.7
8.7
10.3
11.8
13.0
14.4
15.4
16.4
18.2
20.0
21.5
22.7
24.0
25.3
26.4
30
0.0
2.6
5.0
7.0
8.7
10.2
11.6
12.8
13.8
15.0
16.7
18.4
20.0
21.2
22.6
23.7
25.0
40
0.0
1.0
3.7
5.7
7.4
8.8
10.0
11.5
12.4
13.6
15.5
17.0
18.7
20.0
21.4
22.3
23.6
50
0.0
0.0
2.5
4.6
6.3
7.8
9.0
10.4
11.4
12.5
14.4
16.0
17.7
19.0
20.4
21.6
22.7
75
0.0
0.0
0.0
2.2
3.8
5.4
6.7
8.0
9.0
10.0
11.0
13.8
15.6
16.8
18.2
19.5
20.5
100
0.0
0.0
0.0
0.0
1.7
2.3
4.6
6.0
7.0
8.2
10.0
12.0
13.5
15.0
16.4
17.5
18.7
125
0.0
0.0
0.0
0.0
0.0
1.6
3.0
4.4
5.4
6.6
8.5
10.4
12.0
13.4
14.6
16.0
17.3
150
0.0
0.0
0.0
0.0
0.0
0.0
1.5
2.8
3.8
5.0
7.0
8.9
10.5
12.0
13.4
14.7
16.0
* The vessel used to receive high pressure condensate, and flash steam which can be used at lower pressures
for additional heating, is called a flash tank.
Figure 2.8
Water hammer can result from accumulation of condensate in a sagging steam main
12
Yarway Industrial steam trapping handbook
Chapter 2 - Basics of steam and steam systems
• Air: boilers and steam systems are full of
air prior to startup. An especially important
part of getting any steam system operating
efficiently is the removal of air from it. Air is
a poor conductor of heat, and mixtures of air
and steam have less heat content than steam
alone at the same pressure. Both of these
factors have an especially adverse affect on
heat transfer rates. Air is eliminated from
the steam system by thermostatic air vents
and by steam traps. Some traps are much
more effective air eliminators than others,
a subject which is discussed in greater
detail in Chapter 3, Operating principles
of steam traps.
• Gases: carbon dioxide and oxygen are both
present in steam systems. Free oxygen
is a normal constituent of water but it is
principally the boiling process that volatilizes
the carbonates in water to produce carbon
dioxide. Both· gases foster corrosion. An
important function of a steam trap is to assist
in the purging of these noncondensable gases
from the steam system.
• Corrosion: all steam systems and their
associated components suffer from the
effects of corrosion. Corrosion attacks boiler
tubes, steam mains, heat exchangers, valve
components and fittings such as steam
traps. Over time all these items succumb.
The primary defense is a carefully monitored
and maintained boiler feedwater treatment
system that controls the gases (oxygen and
carbon dioxide) which promote corrosion.
Carbon dioxide by itself is not corrosive, but
it can combine with free hydrogen to form
carbonic acid which is corrosive. A principal
reason stainless steel is used extensively in
steam traps is to resist the effect of corrosion
and prolong the life of the trap.
• Dirt: the trash and accumulated debris
in a newly piped steam system must be
seen to be believed. In older systems dirt,
corrosion products, and sealants from
the maintenance repair of a leaky joint,
continue to plague such components as
small valves, instruments and steam traps.
These devices with their small clearances and
vulnerable seating surfaces are especially
susceptible to dirt related failures. Dirt which
prevents the free movement of internal parts
or which gets caught between the valve and
seat sealing surfaces leading to erosion
damage is a major source of problems.
With good reason, the knowledgeable user
places a pipeline strainer upstream of each
steam trap.
Yarway Model 151
Summary
A basic knowledge of the properties of steam
and the problems of steam systems is an
essential foundation to a good understanding
of steam trapping.
Concepts such as the significantly greater
heat content of steam over condensate (at the
same temperature) and the predictable affect
of pressure changes on steam and condensate
formation (as shown by the saturation curve)
are important. It is when these principles are
violated that steam heating and steam trapping
problems develop.
Flash steam is useful when properly directed
and a problem when it is not. In addition, it
is confusing to the field technician checking
steam trap performance. Here, experience is
the best teacher.
All steam systems must deal with problems
of corrosion, air and gas venting, dirt (usually
corrosion products) and water hammer. Steam
traps are both a victim of these problems as
well as potential solution contributors – it is
knowledge of good practice that will decide
whether they are part of the problem or part of
the solution.
Emerson’s goal in writing this book is to inform
the engineer on useful tools and tips to using
steam traps correctly.
13
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Chapter 3 – Introduction
Steam traps are an important element of any
steam system. They are expected to perform
a vital function with an absolute minimum of
attention. If properly selected, sized, installed
and maintained, traps can provide many years
of trouble-free service. A clear understanding
of their working principles with their inherent
advantages and limitations will greatly simplify
the processes of selecting a proper trap,
solving system problems and diagnosing
trap malfunctions.
Definition
A steam trap can be defined as a self-contained
valve which automatically drains condensate
and discharges air and noncondensible gases
from a steam-containing pipe or vessel. It
remains closed in the presence of steam. In
some designs, however, it will allow steam
to flow at a controlled or adjusted rate.
While this statement defines the basic functions
of a steam trap, it should be understood that
the device must be capable of operating at
pressures ranging from a vacuum to 4500 psi
and pass condensate loads ranging from
zero (under superheated conditions) to as
high as 100,000 lb/hr for certain process
equipment. Actual installations vary as well.
Some traps will see service at constant
pressure and condensate load. Others will
need to accommodate variations in pressure
and condensate load and may be installed in
systems that are shut down frequently. Clearly,
no single device can serve all needs. A variety
of types, sizes and configurations is necessary
to satisfy all conditions.
Yarway Model 711UCF2
Basic steam trap types
Over the years, three basic trap types have
evolved and have been classified according
to their mode of operation. Certain types of
traps may combine two working principles
in their operation. Within the scope of this
book, however, the predominant condensate
discharge principle shall designate the trap
type. The three types are:
• Thermodynamic traps: traps that are
actuated by the principles of thermodynamics
and fluid dynamics.
• Mechanical traps: traps that are actuated by
a float, responding to changes in condensate
level.
• Thermostatic traps: traps that are actuated
by temperature sensitive devices, responding
to changes in condensate temperature.
Thermodynamic traps
Thermodynamic traps are phase detectors in
that they can discriminate between liquids and
gases. But they do not discriminate between
steam and air or other noncondensible
gases. Therefore they have a reduced ability
to bleed-off those gases. Minute amounts of
steam may also be passed. The thermodynamic
working principle is simple and, with only one
moving part, these small devices are rugged.
There are three basic types of thermodynamic
traps. They differ from one another by the
configuration of the valve they use to open
and close a port. Each is well adapted to a
particular set of service conditions.
14
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
1. Disc traps: disc traps utilize the heat energy
in hot condensate and the kinetic energy in
steam to open and close a valve disc. They
are phase detectors, sensing the difference
between liquid and gas or vapor.
During initial startup, pressure created by
cold condensate pushes the valve disc off the
seating surface. This uncovers the inlet and
outlet ports, allowing discharge. As condensate
reaches the inlet port (a restriction), it
experiences a decrease in pressure and an
increase in velocity (in accordance with the
laws of fluid dynamics). If the condensate is
very close to steam temperature, the lower
pressure will cause it to flash into steam (in
accordance with the laws of thermodynamics).
The resulting high velocity flow beneath the
disc, with its attendant localized pressure
reduction under the disc, causes it to snap
shut. Flow through the trap then stops until the
pressure in the chamber over the disc decays
sufficiently to allow the inlet pressure to force
the disc off its seat. Condensate then flows
through the trap until once again it reaches
such a velocity and lowering of pressure that
flashing occurs and the disc can snap shut.
This cycle continuously repeats itself the disc
opening to allow the flow of condensate, and
closing on high velocity flash steam.
Disc traps are most frequently used in light
condensate load applications and are known
as 'hot' traps – i.e., quickly discharging very hot
condensate immediately after it forms.
Yarway Model 721
Advantages
• Failure mode, gradually, predictably
open over time.
• Simple construction.
• Small size and light weight.
• Can be mounted in any position.
• Rugged, withstands water hammer.
• Self draining, not damaged by freezing.
• Function not impaired by superheat.
• Versatile, suitable for wide pressure range.
• Condensate discharge temperature closely
follows the saturation curve.
• Performance is easily checked in field.
Disadvantages
• Marginal air handling capability.
• Excessive back pressure in return systems
can prevent trap from closing.
• Life is reduced significantly as pressures
move above 300 psi.
• High discharge noise level.
• Dirt particles can increase cycle rate
causing wear.
Figure 3.1
Disc trap
Flash vapor
closes valve disc
Seating surface
Valve disc
Liquid condensate
and flash out
Steam and
condensate in
Inlet port
Outlet port
15
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
2. Piston traps: piston traps utilize the heat
energy in hot condensate, and the kinetic
energy in steam, to open and close a valve.
Like disc traps, they are phase detectors
sensing the difference between a liquid
and gas or vapor.
During initial startup, pressure created by the
cold condensate lifts the piston valve, allowing
discharge of condensate. During this phase,
the control chamber pressure is low because
the second or control orifice, can discharge
more condensate than can be supplied to
the control chamber through the first orifice.
When the temperature of the discharging
condensate is very close to steam temperature
(i.e., saturation temperature), the condensate,
experiencing the lower pressure of the control
chamber, will change into flash steam (in
accordance with the laws of thermodynamics).
This flashing of the condensate in the control
chamber chokes the flow through the control
orifice, causing an increase in control chamber
pressure. This increased pressure, acting
on a larger effective area of the piston valve
than the inlet pressure, causes it to snap
shut – preventing steam flow through the
trap. When cooler condensate reaches the
trap, causing the control chamber pressure to
drop, flashing ceases and the trap re-opens to
repeat the cycle.
The control orifice provides a continuous
discharge which is helpful in passing air or
other non-condensable gases during startup.
Figure 3.2
Piston trap
The piston valve remains closed in the
presence of steam because the pressure on top
of the piston acts on a larger effective area than
the inlet pressure under it. Steam loss through
the control orifice is minimal.
Introduced in the 1930’s the piston trap was
the first thermodynamic trap. It is a 'hot' trap,
providing excellent service in high pressure
applications.
Advantages
• Suitable for high pressure.
• Can be mounted in any position.
• Good response to changing condensate load
conditions.
• Rugged, withstands water hammer.
• Self-draining, not damaged by freezing.
• Function not impaired by superheat.
• Good air handling capability.
• Primary failure mode-open.
• Small size and light weight.
Disadvantages
• Excessive back pressure in return systems
can prevent trap from closing.
• Condensate discharge temperature follows
the saturation curve over a limited range.
• Difficult to field check because of continuous
control flow discharge.
Flash vapor closes
piston valve
Control chamber
Piston valve
Second orifice
(control orifice)
Steam and
condensate in
Liquid condensate
and flash out
16
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
3. Lever traps: lever traps are a variation
of the thermodynamic piston trap. They
operate on the same principle as piston
traps but with a lever action rather than
a reciprocating piston action.
When the lever is closed, there is a limited
flow through the annulus between the inlet
valve and its seat (first orifice) which then
enters the control chamber and flows out
through the second or control orifice. Incoming
condensate pushes the lever upward with a
tilting motion and full flow goes under it and
out the discharge port. Condensate flowing
past the inlet seat (a restriction) experiences a
pressure drop (in accordance with the laws of
fluid dynamics) and it will flash into steam (in
accordance with the laws of thermodynamics)
when the condensate temperature is very close
to steam temperature (saturation temperature).
The localized lower pressure under the lever
(created by the high velocity flow of flash steam)
causes the lever and inlet valve to snap shut.
This prevents steam flow through the trap.
When condensate with its cooler temperature
again reaches the trap, it will reopen, repeating
the cycle.
Figure 3.3
Lever trap
The control orifice has a continuous discharge
which is helpful in passing air and other
noncondensible gases during startup. Steam
loss through the control orifice is minimal.
Lever traps are designed for applications
having especially large condensate loads and
that benefit from the very rapid discharge of
condensate after its formation.
Advantages
• Suitable for high pressure applications.
• Good response to changing condensate
load conditions.
• Rugged, withstands water hammer.
• Not damaged by freezing.
• Function not impaired by superheat.
• Good air handling capability.
• Small, compact, easy to install and service.
Disadvantages
• Excessive back pressure in return systems
can prevent trap from closing.
• Difficult to field check due to continuous
control flow discharge.
• Can only be mounted in one position.
Upper chamber
Control orifice
Lever valve
Liquid condensate
and flash out
Steam and
condensate in
Inlet valve
Outlet orifice
17
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Mechanical traps
Mechanical traps are density detectors and
therefore also have difficulties venting air
and noncondensible gases. Mechanical traps
employ either an open or a closed float to
actuate a valve. Closed float mechanical traps
usually employ a secondary thermostatic air
vent which allows the trap to discharge air
rapidly. The air vent, of course, is an extra
component which can fail open, causing the
loss of steam, or fail closed and prevent the
trap from discharging condensate. Closed float
traps are usually large in physical size. This,
combined with a float that is fragile to external
pressure, and the continuous presence of
condensate within the trap, make this device
unsuitable for high pressure applications
or installations where water hammer or
freeze-ups can be expected.
On the positive side, these devices respond to
changes in condensate level only, independent
of temperature or pressure. They respond
rapidly to changing loads. Condensate
discharge temperatures follow closely the
saturation curve and they have a modulating
(rather than an on-off) type of discharge.
They are extremely energy efficient.
Open float mechanical traps share many
characteristics with closed float traps. One
major difference, of course, is the open float
as found in an inverted bucket trap. The open
float is no longer a weak point, because it
cannot be collapsed by excessive pressure.
Venting is usually accomplished by means of
a small vent hole in the top of the bucket. This
is a compromise, as the efficiency of the trap
is affected by the sizes of the vent. The larger
the vent the better the air handling, but at the
expense of higher steam losses. A smaller vent
has the opposite effect. The end result is a trap
that is relatively efficient, but which does not
remove air rapidly during startup conditions.
It discharges near steam temperature with an
on-off action and the discharge temperature
follows the saturation curve. All mechanical
traps are position-sensitive and can be
installed only in their intended orientation.
18
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
1. Closed float traps: although it is one of the
oldest on the market, the closed float trap
is still in widespread use. The opening and
closing of the valve is caused by changes of
the condensate level within the trap shell.
When the trap is empty, the weight of the float
closes the valve. As condensate enters the trap,
the float rises and opens the valve, allowing
condensate to be discharged. The float is
designed to provide sufficient force to overcome
the differential pressure across the valve. The
internal float and valve configuration is such
that the condensate level is always above the
valve, thus creating a continuous water seal
at its seat. Actual construction varies widely
depending upon the manufacturer. While most
designs employ a linkage-pivot system, one
particular design uses no linkage at all and
relies on a free floating ball to achieve the
desired action.
An inherent disadvantage of a simple
float trap is that it cannot discharge air or
noncondensible gases. It is therefore necessary
to install an auxiliary thermostatically activated
air vent. For this reason, these traps are known
as float and thermostatic or F and T traps.
Advantages
• Unaffected by sudden or wide pressure
changes.
• Responds very quickly to condensate load
changes.
• Continuous discharge.
• Condensate discharge temperature closely
follows the saturation curve.
• Function is not impaired by high back
pressures.
• Energy efficient.
• Simple construction.
Disadvantages
• Relatively large and heavy.
• Float easily damaged by water hammer.
• Does not withstand freezing.
• Can be mounted only in one position.
• Suitable only for relatively low pressures.
• Requires auxiliary air vent which is an
additional source of failure.
• Primary failure mode is closed.
• Not self-draining.
Figure 3.5
Float and thermostatic trap
Thermostatic air vent
Body
Cover
Valve seat
Float
19
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
2. Inverted bucket traps: inverted bucket
traps are members of the mechanical trap
family, using an open 'inverted bucket' as
a float. The trapping principle utilizes the
difference in density between steam and
water.
The construction of the trap is such that the
trap inlet leads into the bottom and open end
of the inverted bucket. Discharge is through an
outlet valve above the inverted bucket.
Steam entering the inverted and submerged
bucket, causes it to float and close the outlet
valve, preventing discharge of steam. Steam in
the bucket both condenses and leaks through
the vent, allowing the bucket to sink and open
the valve to discharge condensate. The weight
of the bucket must be sufficient to overcome
the closing force created by the differential
pressure across the valve. Inverted bucket
traps discharge condensate intermittently
very near saturation temperature.
Any air or noncondensible gases entering
the trap will also cause the bucket to float
and the valve to close. Since they cannot
condense as steam does, those gases
will cause the trap to remain closed.
In order to overcome this problem, the bucket
has a hole to vent air and steam. The size of
this vent hole has to be relatively small to
prevent excessive loss of steam in addition
to the air.
While most inverted bucket traps utilize a
linkage system to obtain their desired action,
one particular design uses no linkage at all and
uses a free-floating open spherically-shaped
float in its design execution.
Advantages
• Simple construction.
• Rugged.
• Condensate discharge temperature closely
follows the saturation curve.
• Reliable.
Disadvantages
• Marginal air handling during startup.
• Not self-draining; subject to freeze-ups.
• Not suitable when superheat is present.
• Can lose prime, and is not self-priming.
• Can be mounted only in a single position.
• Failure mode is unpredictable (open or
closed).
Figure 3.6
Inverted bucket trap
20
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
3. Open bucket trap: open bucket traps are
rarely used today. As with other mechanical
traps, they utilize the difference in density
between steam and water.
When condensate first enters the trap, it fills
the trap body and causes the bucket to rise
and close the valve at the top of the trap. If
entrapped air is removed, condensate will
continue to enter the trap, finally spilling over
into the bucket. This causes it to sink and open
the valve allowing discharge of condensate.
When steam arrives, it pushes the condensate
out of the bucket through the syphon tube,
which in turn refloats the bucket and closes
the valve. As the steam in the trap condenses,
additional condensate enters the trap and the
cycle is repeated.
This type of trap requires an auxiliary
thermostatically activated air vent, similar to
that used in the float and thermostatic trap.
Advantages
• Simple construction.
• Reliable.
• Condensate discharge temperature closely
follows the saturation curve.
• Function not impaired by high back pressure.
• Fast response to changing condensate loads.
Disadvantages
• Not self-draining; subject to freeze-ups.
• Not suitable when superheat is present.
• Can lose prime, not self-priming.
• Can be mounted only in a single position.
• Requires auxiliary air vent which is an
additional source of failure.
• Suitable only for relatively low pressures.
• Relatively large and heavy.
Figure 3.7
Open bucket trap
Valve
Seat
Liquid condensate
and flash out
A
Air vent
Steam and
condensate in
Steam space
Condensate level
Syphon tube
Open bucket
21
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Thermostatic traps
Thermostatic traps respond to changes in
temperature and therefore discriminate very
well between steam and cooler noncondensible
gases. They can rapidly purge air from a
system, especially on a cold startup, and
can be installed in various positions. Most
frequently, actuation is by means of a bimetallic
element or a bellowslike capsule filled with a
vaporizing liquid.
Bimetallic actuated devices are characterized
by their high resistance to damage from
freeze-ups, water hammer and superheat. They
are relatively small in size and lend themselves
to high pressure designs. The condensate
discharge temperature, however, does not
follow the saturation curve very well, and the
bimetallic elements are subject to corrosion
with some reduction in closing force over time.
Bellows actuated traps, on the other hand,
discharge condensate at a temperature which
follows the saturation curve. The weak point
is the bellows itself which can be damaged by
superheat, water hammer or freeze-ups.
Thermostatic traps respond slowly to changing
conditions even though the cause is usually
misunderstood. It is not the heat sensitive
element that is slow to respond. Rather it is the
heat energy in the condensate inside the trap,
which is slow to dissipate, that causes the time
delay. Insulating thermostatic traps reduces
their responsiveness even more. Mounting the
trap at the end of a cooling leg in an area where
air can circulate improves responsiveness
and is the basis for installation instructions
recommending a cooling leg at least three
feet in length.
Figure 3.8
Cross-sectioned bimetallic actuated trap;
a simple thermostatic
Figure 3.9
Yarway Model 151
Yarway Model SP80
Yarway Model 151A
22
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
1. Bimetallic: bimetallic steam traps utilize
the sensible heat in the condensate in
conjunction with line pressure to open
and close a valve mechanism.
The valve and seat system is usually arranged
to produce a 'flow under the seat' condition.
Supply pressure, in other words, tends to
open the valve. The bimetallic elements are
in the form of small discs and are arranged
to produce a closing force with increasing
temperature. This closing force is in opposition
to the opening force created by the supply
pressure. Some bimetallic traps use a single
leaf element rather than the stacked disc
elements shown in Figure 3.10.
The traps are generally factory-adjusted so that
at saturated steam conditions, the temperature
created force of the bimetallic elements
prevails, closing the valve and preventing loss
of steam. As the temperature of the condensate
cools, the line pressure becomes the dominant
force, causing the valve to open and allowing
the discharge of condensate. Back pressure in
a closed return system provides an additional
closing force resulting in a lower opening
temperature than the same trap discharging
to atmosphere. The discharge temperature,
therefore, is affected by back pressure.
A design problem for bimetallic traps is created
by the non-linearity of the saturation curve.
Shaping and stacking techniques of the
bimetallic elements have made it possible for
these traps to have a discharge temperature
that approximates the saturation curve. This
has expanded the useful pressure range of
bimetallic traps without adjustment.
The modern bimetallic trap has many
technical and practical advantages.
Advantages
• Rugged.
• Energy efficient.
• Self-draining.
• Resistant to freeze damage.
• Withstands water hammer.
• Capable of discharge temperature
adjustment.
• Can be mounted in several positions.
• Primary failure mode-open.
Disadvantages
• Dirt particles can prevent tight valve closing.
• Condensate discharge temperatures do not
follow the saturation curve closely.
• Difficult to field check when operating in a
throttling mode.
• Condensate discharge temperature is made
lower as back pressure increases.
• Relatively slow response to changing
condensate loads.
• Bimetallic elements are relatively
susceptible to corrosion.
Figure 3.10
Bimetallic trap
23
Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
2. Bellows traps: bellows traps are
thermostatic traps that respond to changes
in the temperature and pressure of the
steam supply to open and close a valve.
The valve actuator is a capsule or bellows
filled with a vaporizing liquid, and having
both a fixed and a free moving end, it opens
or closes the valve in response to internal
pressure changes. The most frequently
used actuating element is a corrugated
bellows. Single-diaphragm capsules are
also used but provide a correspondingly
shorter stroke.
After such a rupture, the bellows will return to
its natural free length which can be designed so
that the trap will be in either an open or closed
condition.
This simple operating principle provides
many desirable operating characteristics. For
example, the number of degrees below steam
temperature at which the trap will open can
be varied so the trap provides either a 'hot' or
'cold' discharge. Also the normal failure mode
(open or closed) can be changed.
The characteristics of the actuating system
can be affected by the liquid fill and natural
free length of the actuator. The principles can
best be explained by considering a bellows,
even though they apply equally well to single
diaphragm capsules.
The Yarway bellows traps have been improved
in design, construction and materials to
minimize their inherent disadvantages. Today
they play an important role in steam trap
application.
Low boiling point liquids, such as alcohols or
ether, are frequently used in bellows but have
the disadvantage that their saturation curve
does not exactly correspond to that of steam.
As a result steam traps having such a bellows
will discharge condensate having different
levels of subcooling over a wide pressure
range.
Concepts defined
• Natural free length: length of the bellows
assembly before it is sealed.
• Assembled free length: length of the
bellows assembly after it is sealed, in its
cold (contracted) condition.
In the most common arrangement, the bellows
is located upstream of the valve and thus
senses upstream conditions. Flow direction is
over the seat tending to close the valve. During
cold startup, the bellows is contracted, allowing
condensate and air to be discharged. As the
temperature of the flowing medium rises,
the bellows also gets hot, the liquid inside it
vaporizes and expands (strokes) the bellows
to close the valve. Failure of this type of trap
generally refers to the rupture of the bellows.
• Fail open design: this definition implies that
the natural free length must contract the
bellows away from the seat. To make this
arrangement functional, the bellows must
be filled with a liquid having a boiling point
lower that of water, because for the bellows
to expand, the internal pressure must be
higher than the external steam pressure.
Advantages
• Excellent air handling capability.
• Energy efficient.
• Self-draining.
• Various condensate discharge temperatures
available depending on bellows design.
• Condensate discharge temperature follows
the saturation curve.
• Can be mounted in several positions.
• Simple construction.
• Small size and weight.
Disadvantages
• Bellows elements tend to be failure prone,
especially when subjected to water hammer.
• Difficult to field check when operating in a
throttling mode.
• Generally not suited for high pressure
applications.
• Limited superheat capability.
• Short stroke diaphragm design susceptible
to dirt initiated failures.
• Fail closed design: this definition implies
that the bellows remain expanded upon
rupture. This can be accomplished by
evacuating the bellows initially to obtain a
contracted assembled free length. During
normal operation when the bellows is hot,
the pressure inside the bellows will approach
the steam supply pressure, causing it to
expand. Evacuated bellows are usually filled
with water. The inherent advantage is that the
condensate discharge temperature of traps
having such a bellows will closely follow the
steam saturation curve.
Figure 3.11
Bellows trap
Steam and/or
hot condensate
depending on trap
FLOW
Steam and
condensate in
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Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
3. Liquid or solid expansion trap (wax
capsule type): liquid or solid expansion
traps are finding limited application today.
The opening and closing of these traps is a
function of temperature and balanced return
spring forces. Elevated temperatures cause an
expansion of the thermostatic element which
closes the valve, while low temperatures cause
a contraction of the element, aided by the
spring, which results in opening the valve.
Traditionally, the thermostatic actuator has
been in the form of a metal rod, having a
high thermal coefficient of expansion, or
an elastic metallic capsule (bellows) filled
with a liquid which expands when heated. In
recent years design innovation has introduced
a small diaphragm actuator filled with a
wax-like substance which expands rapidly at a
preselected temperature. This has significantly
reduced trap size and increased the speed
of response relative to the more traditional
design. Figure 3.12 shows the working internals
typical of a newer wax capsule expansion trap.
Regardless of design variations, these traps
have one characteristic in common. The
temperature of the condensate they discharge
remains constant at a predetermined point
and is not a function of steam supply pressure.
All other steam trap types have a condensate
discharge temperature that increases with
steam supply pressure.
In general, these constant discharge
temperature traps respond slowly to changes
in temperature and should only be specified
where subcooled discharge with resultant
condensate back-up is desired.
Advantages
• Rugged.
• Good air handling capability.
• Resistant to freeze damage.
• Withstands water hammer.
• Can be mounted in any position.
• Self-draining.
• Primary failure mode is open.
Disadvantages
• Dirt particles can prevent tight close.
• Requires substantial subcooling.
• Difficult to field check.
• Slow response to changing condensate loads.
• Actuator damaged by exposure to high
temperature.
Figure 3.12
Wax capsule trap
Adjustment mechanism
Thermostatic element
Over temperature spring
Return spring
Seat
Valve plug
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Yarway Industrial steam trapping handbook
Chapter 3 - Operating principles of steam traps
Orifice traps
Orifice traps are seldom used because of their
inherent limitations in application range. This
device consists of one or more successive
orifices. Where two or more orifices are used,
condensate passes through a number of
successive chambers where flashing occurs.
This, in turn, creates a restricting or choking
effect and allows the use of larger and less
dirt sensitive orifices for a given condensate
capacity. In some design executions, these
orifices are adjustable valves.
Figure 3.13
Fixed orifice trap
Steam, flash, or liquid in
intermediate chamber
Steam and/or
condensate and
flashing vapor out
Steam and
condensate in
First orifice
Advantages
• No moving parts.
• Suitable for high pressure application.
• Rugged, withstands water hammer.
• Not damaged by freezing.
• Function not impaired by superheat.
• Can be mounted in any position.
Second orifice
Disadvantages
• Orifice size must be carefully selected for
each installation.
• Cannot respond to varying condensate loads.
• Inefficient if oversized.
• Dirt particles readily impair performance.
• Difficult to field check because of continuous
discharge.
• In the absence of condensate, the trap
passes live steam.
A steam trap designer’s comments
Most engineering solutions are a compromise
in one form or another and steam traps are no
exception. The end result is usually a practical
balance between operating characteristics,
utility and cost.
In the preceding discussion, inherent
advantages and disadvantages associated with
the various trap technologies are presented
with very few qualifications. However over
the years, engineers have been ingenious in
finding ways to diminish many of the inherent
shortcomings while enhancing many of the
advantages. The result has been an extension
of the utility of all the various steam trap types.
The influence of standards setting
organizations
In recent years, voluntary standards-setting
organizations have become increasingly
interested in steam trap design, testing and
performance. Responsible steam trap designers
and manufacturers are guided in their activities
by the work of these organizations. The
American National Standards Institute’s ANSI/
FCI Std. 69-1 and ANSI/ASME PTC 39.1 are two
standards that presently relate to steam traps
in the United States. The former is broadly
concerned with the design and safety of steam
traps while the latter is specifically focused on
the issues of measuring a trap’s condensate
capacity and steam losses.
Summary
Steam traps are automatic valves that open in
the presence of condensate and close in the
presence of steam. They should also be able
to pass air without passing steam, although
some types compromise on this point. Typically
they employ one of three basic operating
principles – thermostatic, thermodynamic or
mechanical – to open or close a valve. Each
principle has certain inherent advantages and
disadvantages that makes traps of its type
more suitable for certain applications than the
others. Some trap types combine two principles
in an effort to improve overall performance.
A basic understanding of how each type of
trap works greatly strengthens the ability to
select the optimum trap for each application.
It is also essential knowledge when attempting
diagnostic troubleshooting of steam traps or
steam trapping systems.
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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Chapter 4 – Introduction
The actual procedure of matching a steam trap
to the needs of the application is to perform
the 'sizing' first and the 'selection' second.
Basic definitions of sizing and selection are
presented in that sequence. However, to have a
more complete background and understanding
of the situation, the Application Range is
first discussed in some detail, followed by a
discussion on the Selection Process, and then
the Basic Sizing Steps. You are also referred
to Appendix A for more detailed profiles on
specific applications.
Steam trap application is the process of
matching a steam trap to the needs of a steam
system and its associated equipment.
This involves a two-step process:
1. Sizing it correctly
2. Selecting a suitable type of steam trap
These steps are described in detail in this
chapter. However, it must be emphasized that
two additional steps are required to assure
successful steam trapping results. Chapter 5
discusses the elements that are important
to the proper installation of a steam trap and
Chapter 6 describes the key to long-term
success – proper maintenance.
Sizing and selection of the correct trap for
a given application can be complicated by
a number of variables, but there are some
guiding principles that can make for a logical
selection process. They will be discussed in
this chapter. Some simplifying rules of thumb,
which can be helpful when quick decisions
must be made, will also be presented.
Basic definitions
• Steam trap sizing: this is the process of
choosing a trap which has the capabilities to
meet the operating conditions of pressure,
temperature and condensate drainage rate
for a given application.
Steam trap sizing has been mistakenly limited
by many to matching the end connection size
of a trap to the particular pipe size being used
to drain a piece of steam heated equipment.
Sizing in its correct sense is matching the
steam condensing rate (in pounds per hour)
of a piece of equipment (at its particular
pressure and temperature conditions) to the
rated condensate discharge capabilities of a
suitable steam trap.
Trap manufacturers are prepared to
make sizing calculations to determine
condensate loads in support of their selling
efforts. Small plants having only a few
stream traps tend to rely heavily on the
trap manufacturer for sizing guidance.
Engineering contractors and large plants
using many steam traps generally make their
own sizing calculations. Examples of several
sizing calculations are shown later in this
chapter.
• Steam trap selection: this is primarily the
process of choosing the type of trap, from one
of the major trap technologies (mechanical,
thermostatic, thermodynamic) that will
provide the combination of performance
characteristics most closely matching the
needs of both plant and equipment.
Selection secondarily includes making
judgments about the usefulness of certain
accessories and features which are included
in some trap designs, as well as making
judgments about the advantages of choosing
to do business with one trap manufacturer in
preference to another.
Trap application range
It is possible to classify steam trap applications
in a number of different ways. This book
addresses itself to the field of indus­trial steam
trapping in contrast to the steam trapping
associated with the low pressure (below 15 psi)
heating, ventilating and air conditioning field.
There is some overlap, of course, but industry
has tended to recognize these two major
classifications of users.
Industrial steam trapping applications are
themselves typically divided into two major
classifications:
Protection service
• Steam main drip: drainage of the condensate
that normally forms in the pipes delivering
steam from a boiler to a specific point of use.
This helps prevent damaging water hammer
and promotes the delivery of dryer steam to
plant equipment.
• Steam tracing: drainage of the condensate
that normally forms in the small steam
lines or steam jackets used to heat valves,
field instruments, and the liquids in larger
pipelines during freezing conditions or when
product temperatures must be maintained at
specified levels.
Process service
• Steam using equipment: drainage of the
condensate that normally forms when steam
is used to heat liquids, gases or solids.
These various classifications of steam traps
are presented in the simplified matrix shown in
Figure 4.1.
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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Figure 4.1
Industrial steam trapping range
Service
Protection
Process
Characteristics of service
Small, steady condensate loads
infrequent shutdowns lower
pressures (tracing) and higher
pressures steam main drips.
Application
Steam main drips.
Steam heats air/gas indirectly through
a metal wall.
Steam heats a solid or slurry indirectly
Description
Drainage of condensate from pipes used to transfer steam from
a boiler to its point of use.
Drainage of the condensate that normally forms in the small steam
lines used to heat valves, field instruments, and the liquids in larger
pipelines during freezing conditions. Or when product temperatures
must be maintained above specified levels.
Shell and tube heat exchangers.
Submerged coils.
Jacketed kettles.
Plain or finned coils.
Unit heaters or air blast coils.
Rotating cylinders for paper or textiles.
Larger and fluctuating condensate
loads. Frequent startups are
common, good air handling
required.
Steam heats a liquid indirectly through
a metal wall.
through a metal wall to dry, cure or form.
Steam heats a solid through direct contact
to dry, clean or sterilize.
Plattens or presses for plastics; particle board and similar materials.
Autoclave.
Sterilizer.
Steam tracing.
Figure 4.2
Industrial trapping applications range
Steam pressures
Low
15 psi-100 psi
Medium
100 psi-300 psi
High
300 psi-600 psi
Very High
Over 600 psi
Low
0 to 100 lb/hr
Tracing and drip
Condensate load
Medium
Heavy
100 lb/hr to 1,000 lb/hr
1,000 lb/hr to 10,000 lb/hr
Process applications
Tracing and drip
Process applications
Drip
Process applications
Very heavy
over 10,000 lb/hr
Drip
An alternative way of looking at the steam
trap application universe is by classifications
of steam pressure and condensate load.
Figure 4.2 shows the ranges of pressure and
load most commonly encountered in different
applications. By its very nature such a matrix
tends to be arbitrary, but it does show the
general picture.
If the number of traps in the industrial world
were summarized by steam pressure and
condensate load, and listed in the appropriate
quadrant of the matrix, the largest numbers
by far would be in the low pressure, low
condensate load quadrant. The numbers would
rapidly decrease as the loads and pressure
increase.
Since no single trap design or principle of
operation is suitable for use across such a
wide range of pressures and condensate
loads, preparation of a matrix similar to
Figure 4.2 is sometimes used as a technique
to assist a large plant in standardizing on the
smallest variety of traps for its use. Chapter 6,
Maintenance, describes further the process of
establishing plant standards.
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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
The steam trap selection process
The steam trap selection process starts with
a description of a plant’s need. Unfortunately,
simply stating that need in terms of equipment
to be served – such as a soup kettle, tire
vulcanizing press, or an air heater – is not
adequate. While it is important information,
it is not sufficient to assure that all the
requirements of a specific installation will be
met in a satisfactory manner.
Selecting a trap, like selecting an automobile,
requires an indication of user preference with
respect to a rather large number of criteria.
Fuel economy versus performance, comfort
and safety versus cost, latest style versus an
established model with proven reliability are
familiar car selecting choices. While the factors
that are evaluated in selecting a steam trap
are not nearly as familiar, they are no less
important in making a successful decision.
They can be classified into several levels of
importance. Such a list can then be used as
a basis for assuring that all the significant
requirements of a particular application
are considered. Figure 4.3 summarizes and
classifies the most significant steam trap
selection criteria.
It is important to understand fully the
implications of the selection criteria
summarized in Figure 4.3 if a systematic
selection process is to be successful. The
importance assigned to those criteria listed
as affecting overall utility will vary from plant
to plant and from application to application –
and properly so. Conditions vary from plant to
plant and application to application. Equally
important – perhaps most important –
management philosophies vary. All want high
system efficiencies and low maintenance
costs, but their views vary as to the best way
to achieve these objectives. The significant
point is that it is the weight or value assigned
by the user to the differing criteria that will
shape the decision as to whether a mechanical,
thermostatic or thermodynamic trap will be
selected for a particular application.
A more detailed discussion of the steam trap
selection criteria listed in Figure 4.3 is provided
below:
• Safety: product safety results when a good
design is well manufactured and properly
used. In the United States, the American
National Standards Institute (ANSI) describes
for the manufacturer both design and testing
standards that relate to factors affecting
product safety. Manufacturers can describe
installation and maintenance practices they
know to be successful, but safety in the plant
ultimately rests with the user.
Figure 4.3
Steam trap selection criteria
First level criteria
• Safety
• Efficiency
• Service life
Second level criteria
• Ease of checking
• Sensitivity to back pressure
• Resistance to freeze damage
• Dirt sensitivity
• Installation versatility
• Air venting
• Responsiveness to changing loads
• Resistance to shock vibration and water hammer
• Predominant failure mode
• Discharge mode
• Condensate discharge temperature relative
to saturation curve
• Magnitude of condensate subcooling
• Ease of maintenance
• Supplementing accessories or features
Third level criteria
• Product availability
• Post-sales service
• Warranty
• Price
Satisfy primary requirements
These criteria are least subject to compromise.
All trap types (mechanical, thermostatic,
thermodynamic) are capable of providing excellent
performance in a range of applications when
properly sized and installed.
Affect overall utility
These criteria relate to a steam trap’s overall
utility. The differences between mechanical,
thermodynamic and thermostatic trap designs are
significant. Each trap type has its strengths and
weaknesses. These second level criteria are of
particular interest to the user who is looking beyond
'first cost' and who makes an evaluation based on
'installed' or 'life cycle' costs.
Commercial considerations
These are the commercial criteria that lead to the
selection of one supplier over another.
• Service life: a long lasting steam trap is
obviously desirable. Regardless of design,
however, every steam trap’s life is shortened
as steam pressures and temperatures
increase. Hot condensate is a particularly
difficult liquid to handle. It can be both
corrosive and erosive and, under certain
conditions, it can cause cavitation. It can
destroy valves and seating faces in a matter
of days in extreme circumstances. The
frequency with which a trap must open and
shut also obviously influences its life span.
Opposing these destructive forces are the
designer’s skills, hardened materials and
the level of special concern a plant has for
selecting and sizing traps suitable for the
conditions they will experience.
• Efficiency: the most efficient steam trap is
one that has failed in the closed position
because it wastes no steam. Obviously
efficiency can not properly be considered
without reference to how a trap performs its
other functions. Claims that one trap type is
more efficient than another are as difficult
to support as they are to refute. Given a
calorimeter test in a laboratory, virtually
every major trap type can achieve efficiencies
of or close to 100%. In fact, the differences
in efficiency between traps will often be
unmeasurable because they are less than the
accuracies of the testing equipment.
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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
If there is one trap type that is theoretically
superior from the standpoint of efficiency,
it is probably the thermostatic because its
opening temperature can be below steam
temperature. As a consequence, it can be
made to back up sufficient condensate that
steam is unable to reach the trap and pass
through it in normal service. This condensate
backup, however, is not always desirable
because it may adversely affect the efficiency
of the system. Thermal efficiency of the
steam system in which a steam trap is
installed is more important to the user than
the efficiency of the steam trap. A steam
trap may be very efficient but if it backs
condensate into a heat exchanger – thereby
reducing system efficiency – it is unsuited
for this particular application. The same trap
backing up condensate in certain tracing
applications can be contributing to system
efficiency by utilizing the sensible heat in the
condensate. Clearly, steam trap efficiency is
very important, but overall system efficiency
is even more important, and steam trap
selection should be made with this fact
in mind.
• Ease of checking: considering the difficulties
inherent in detecting whether a steam
trap is performing properly (see Chapter 6
'Maintenance'), it is surprising more
consideration isn’t given to this criterion. A
trap that has a crisp open-close cycle can
quickly be judged to be healthy with a simple
listening device. Traps that modulate or have
a slower and softer open-close cycle often
leave the steam trap checker uncertain about
their condition. “Is it capable of shutting off
tightly?” is the nagging question. As a group,
traps that normally provide modulating
control such as the float and thermostatic or
the bimetallic thermostatic are more difficult
to check than other trap types.
• Sensitivity to back pressure: traps
discharging into closed condensate return
systems will experience varying amounts
of back pressure, depending on the return
system’s design and the number and
condition of other traps discharging into
it. Most bimetallic traps will discharge
condensate at progressively cooler
temperatures as they experience increasing
back pressures. Thermodynamic traps tend
to decline in efficiency as back pressures
exceed 50% of the inlet pressure.
• Resistance to freeze damage: steam
lines shut down for maintenance or by
accident, or condensate return lines
reduced to very slow or sluggish flow
because of dirt or accumulated scale, are
all subject to freezing in cold weather.
The degree of concern by plant managers for
damage to equipment and lost production is
quite different between the Gulf Coast and
Canada for obvious reasons. Some steam
traps are inherently more susceptible to
damage by freezing than others by virtue of
their design and materials of construction.
Cast iron body bucket and float traps are
not popular for use out of doors in cold
climates because they require an internal
water reservoir which makes them especially
vulnerable to freezing problems. In addition,
the piping configuration used for their
installation often makes system drainage
difficult. By contrast, bimetallic thermostatic
and thermodynamic traps are free of this
problem.
• Dirt sensitivity: all steam traps can be put
out of commission by pipeline scale, pipe
joint sealants, oxide build-up or similar forms
of contamination. Typically, dirt is caught
between a trap’s valve and seat. This prevents
tight shut-off, allows steam leakage and very
quickly causes permanent erosion damage
to these sealing faces. Some thermostatic,
thermodynamic and bucket traps will have
their smaller passage or vent holes closed by
oxide build-up. Knowledgeable engineers will
carefully consider the relative susceptibility
of various trap types to contamination by
dirt before selecting a trap for their plant.
• Installation versatility: some steam
trap models (such as thermostatic or
thermodynamic types), can be installed
successfully in either a horizontal or
vertical line. This simplifies the inventory,
storekeeping and installation problems of
the plant. Mechanical traps do not easily
lend themselves to this flexibility of use, thus
often creating the need for specific models
for installation into either horizontal or
vertical lines.
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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
• Air venting: in startup situations, air must be
vented from pipe lines and equipment before
steam can enter it. The faster it is vented,
the more quickly equipment is brought up
to temperature. Some steam traps – such
as thermostatic types – pass air very quickly
under these conditions, while thermodynamic
disc traps and bucket traps release air much
more slowly. If equipment is started and
shutdown frequently, as in many process
applications, good air venting is an especially
important consideration in determining the
type of trap to be installed.
Installations which operate around the clock
for months at a time are less concerned with
this special startup capability, but they still
require the ability to pass non-condensable
gases such as carbon dioxide (CO2) that may
accumulate in a condensate return system.
• Responsiveness to changing loads: not all
trap types accommodate themselves quickly
to the changing condensate loads typical
of process applications. Mechanical and
thermodynamic traps are very responsive,
but thermostatic traps must first cool slightly
before they can open wider to pass a greater
amount of condensate. An adequate “cooling
leg” is required in front of thermostatic traps
to assure good system efficiency.
• Resistance to shock, vibration and water
hammer: despite the system designer’s
best efforts, all steam systems tend to
experience some level of vibration, shock, or
water hammer. Startups, pressure changes
or changing loads, are the periods that
generally are the hardest on equipment such
as steam traps. Not all traps, however, are
equally vulnerable to damage from these
causes. Thermodynamic traps and bimetallic
thermostatic traps are generally very rugged.
The bellows in thermostatic traps and the
closed float in some mechanical traps are
fragile and damage-prone. These damage
producing conditions are most frequently
seen in process applications.
• Predominant failure mode: all traps are
susceptible to failing closed when plugged
with dirt. But, apart from this special case,
some types of trap normally fail in the open
position while others will typically fail in
the closed position. Thermodynamic traps
and bimetallic traps fail open when they
are worn out. Bucket traps tend to have an
unpredictable failure mode as they can fail in
the open position with a loss of prime, or they
can fail closed if the bucket vent becomes
clogged or the trap experiences pressure
differentials above that allowable for the
trap’s orifice size. Bellows thermostatic traps
will fail either open or closed depending on
the design of the bellows if the bellows is
damaged.
Opinions differ concerning the desirability
of one failure mode over the other. A trap
'failed closed' is not losing steam. On the
other hand, a trap however wasteful, that has
failed open, maintains condensate drainage
and therefore has not interfered or disrupted
the process. In general, it would seem that
preserving the process is the higher need and
a trap that fails open is more desirable than
one that fails closed.
• Discharge mode (cyclic or modulating
and continuous): does a trap that has a
distinct open and shut cycle provide inherent
advantages or disadvantages relative to
one that has a continuous and modulating
discharge? The cycling thermodynamic disc
and bucket traps are easier to check for
proper performance, and perhaps better at
passing dirt particles. On the other hand, the
continuous draining float trap is especially
responsive to rapidly changing condensate
loads and it does not contribute to pressure
surges in the return system. The judgment as
to which is the superior trap depends on the
relative value that the plant operator assigns
to these various characteristics.
• Condensate discharge temperature relative
to the saturation curve: the temperature
of condensate immediately in front of a
steam trap at the moment it opens is called
the condensate discharge temperature.
Of course the trap is expected to close
after the accumulated condensate has
been drained and before live steam can
be discharged. In general, it is desirable
that this opening and closing cycle take
place at temperatures very close to that
of saturated steam. As the temperature of
saturated steam varies with its respective
steam pressure (see steam saturation curve,
Figure 2.5), it is very desirable that a trap
be able to accommodate these changing
conditions. A trap that does this well is
said to 'follow or parallel the saturation
curve' and is a more versatile device and
more easily applied than one that does not.
Mechanical, some bellows thermostatic,
and most thermodynamic traps follow the
saturation curve closely. Bimetallic traps
can be designed to 'follow the saturation
curve' approximately, but they do not provide
the same range of performance that can be
expected with the other trap types.
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Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
• Magnitude of condensate subcooling: the
terms 'subcooling' and 'suppression' refer
to the temperature difference between
that of condensate at the moment the
trap starts to open and the temperature of
saturated steam (at the same pressure).
For example, a trap operating at 100 psi
(steam saturation temperature 338°F) and
designed for 10 degrees subcooling will
not start to open until the temperature of
condensate at the trap drops to 328°F. A
trap with little subcooling or suppression
will discharge condensate within two or
three degrees of steam temperature, while
a trap with a large amount of subcooling
will discharge condensate at temperatures
30°F or more below steam temperature.
Under most circumstances it is desirable to
discharge condensate as soon as it forms
as this helps in the achievement of steady
temperature control. This fact leads to the
general desirability of a 'hot' trap i.e., one
with only two or three degrees of subcooling
or suppression. Because hot traps discharge
condensate almost as soon as it arrives,
they are rapidly responsive to changing
condensate loads. Condensate is not held
back until it cools 20°F or 30°F before the
trap opens, as is the case with some of the
more slowly responding trap types.
There are a number of applications in the
area of tracing where the heat in highly
subcooled condensate is adequate for
the warming job to be done. Under these
conditions a 'cool' trap will tend to improve
overall system efficiency provided the system
has been specifically designed to achieve
this objective. It is the requirement of the
equipment being served by the steam trap
that will establish whether one level of
subcooling is more desirable than another.
• Ease of maintenance: all steam traps fail in
time. it is a matter of management philosophy
whether they are repaired or scrapped and
replaced. While steam traps are available
in both repairable models and throw-away
versions, the longer economic view favors
repairability. This preference has encouraged
several manufacturers to design traps that
significantly simplify the maintenance task.
• Supplementing accessories or features:
steam traps may be purchased with a variety
of features that increase their life or utility.
Strainers integral to the trap body protect
the trap mechanism from dirt and simplify
field installations. Integral blowdown valves
clean the strainer and help with system
troubleshooting. Integral check valves
provide system protection, sight glasses
aid in verifying proper trap performance,
temperature adjusting capability is available
with some bimetallic traps and auxiliary
thermostatic air vents can be added to certain
bucket traps to improve their air handling
capability. Each option requires evaluation
based on its merits and the needs of the
application and installation.
The steam trap sizing process
Regardless of whether a mechanical,
thermostatic or thermodynamic trap is selected
for a particular application, its satisfactory
performance will depend on it being sized
properly for the pressures, temperatures
and condensate loads it will experience.
For instance:
• Pressure and temperature: safety is
obviously the first consideration. No trap
should be used unless its pressure and
temperature rating equals or exceeds that
of the system into which it will be installed.
Mechanical traps, such as bucket or float
traps, frequently have a maximum operating
pressure that is well below its maximum
design pressure rating. The trap’s utility is
correspondingly restricted to the smaller
rating. These important design and operating
limitations of pressure and temperature are
marked on a trap’s body or nameplate.
• Capacity: the basic objective of the sizing
process is to select a steam trap that will
have a suitable capacity for passing the
condensate created by the particular piece
of equipment being drained. Selecting a
trap with too small a capacity will cause the
backup of condensate, effectively reducing
the area of steam exposed heat transfer
surface. This reduces total system efficiency
and increases freezing and water hammer
risks. Selecting a trap with too large a
capacity, or 'oversizing', not only involves
buying a larger and more costly trap than
necessary, but tends to result in traps that do
not close well and have a shorter than normal
service life. In turn when they fail, they are
large wasters of steam.
32
Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
The basic sizing steps – in detail
In order actually to perform steam trap sizing
calculations, more information is required.
A detailed description of the sizing steps is
given below:
• Step 1:Determine the pressure
conditions at the trap.
Pressure at the inlet of the trap will often be
considerably less than that generated at the
boiler. Pressure reducing valves, cascading
systems, line losses and condensing rates all
work to reduce pressure in the system before
the trap. While it is always important to know
the inlet pressure a trap will experience, it
is especially true in sizing mechanical types
such as bucket or float traps. Their operating
principle requires the weight of the bucket or
float to open their valve. Should differential
pressures be above the rating of the trap, it will
fail in the closed position.
Pressure at the outlet of the trap will range
from below atmospheric to near inlet pressures
depending on the design of the condensate
collection system and the performance of
other equipment connected to it. The effect of
back pressure on a trap’s performance is an
important selection criterion. For example,
excessive back pressures upset the normal
pressure temperature balance of most
bimetallic traps; the increased closing force
results in increased condensate back-up and
increased condensate subcooling. As back
pressures increase beyond design limits,
thermodynamic traps will remain in the
open position.
Figure 4.4
Steam trap capacity changes
20
0°
Fw
ate
r
The basic sizing steps
• Step 1:Determine the inlet and outlet
pressure conditions of the trap.
• Step 2:
Calculate the condensate load
produced by the equipment being
drained.
• Step 3:Select a suitable safety load factor.
• Step 4:Solve the equation:
(condensate load) x (safety load
factor) = desired trap capacity.
• Step 5:
Choose trap from manufacturer’s
catalog with appropriate pressure
and capacity ratings.
Discharge capacity
Factors that affect a steam trap’s capacity
A trap’s capacity to pass condensate is basically
determined by three factors: (1) orifice or seat
size; (2) pressure differential between the inlet
and outlet ends; (3) temperature of condensate.
Because these factors are variables, a
trap’s capacity can properly be stated only
if the differential pressure and condensate
temperatures are also stated. The manner in
which these factors variously influence a trap’s
capacity is described below:
• Orifice or seat size: this has been carefully
established by the trap designer with certain
applications in mind. In the mechanical and
thermodynamic trap, this orifice is fixed
in size. In thermostatic traps (especially
bimetallics), the net orifice area effectively
varies in size as temperature changes slowly
move the valve into or out of the seat.
• Differential pressure: it seems obvious that
the amount of flow through an orifice will
depend on the difference in pressure between
its inlet and outlet. Less obvious (especially
in very large industrial complexes with miles
of steam lines) is what these pressures are
in many steam trap applications. In such
installations, there are many operating
reasons why line pressures will vary. Traps
discharging immediately to atmosphere
have only the inlet pressure in doubt. Traps
discharging into closed condensate return
systems have the added uncertainty of
the level of back pressure in that system.
The significance of these uncertainties is
that properly sizing a steam trap for such
conditions is made more difficult.
• Condensate temperature: the curves in
Figure 4.4 graphically show how much the
capacity of a steam trap can vary simply
because of changes in the temperature of
condensate coming to it. It can be seen that
for a given pressure, the discharge capacity
of a trap will increase as the condensate
temperature decreases below that of
steam temperature. A steam trap under
startup conditions, discharging 200°F water,
can have four times more capacity than
when discharging condensate near steam
temperature (say, at 340°F).
ow
bel
0°F
3
ter
Wa
am
ste
p.
tem
mp.
m te
stea
t
a
er
Wat
0
Pressure
33
e 55
e 55
e 56
e 56
e 55
e 57
e 57
e 56
e 58
e 58
e 57
e 59
e 59
e 58
C=
Q x (T2 – T1)
2
Yarway Industrial steam trapping
handbook
Q x (T2 – T1)
Page 55
C
=
Chapter 4 - Principles of steam trap application 4
C=
• Step 2:
Calculate the condensate load to
be handled – process traps
Various formulas are used to calculate
condensate loads depending on the nature of
the application. Some are technically more
accurate than others because theyPage
employ
55
fewer assumptions about the operating
Page 56
conditions but, in general, most provide
Page 55
acceptable approximations. There are four
broad classifications of heating equipment
discussed on the following pages:
1. Steam heats a liquid indirectly through
a metallic wall
Typical examples: cooking coils, storage tanks,
Page 57
jacketed kettles, stills
Page 56
The following simple formulas are generally
satisfactory for quickly estimating condensate
Page 56
loads when heating water or a petroleum
product:
Water being heated:
C=
Q x (T2 – T1)
Page 58
Q x 2(T2 – T1)
Page 57
C petroleum
=
A
being heated:
Q x 2(T2 – Tproduct
1)
C=
4 –T )
Q x (T
Page 57
2
1
C=
Q x4500 x S g x Sh x (T2 – T1)
C=
When:
Q x 500 x SHgfgx Sh x (T2 – T1)
C = = condensate
load in lb/hr
H fgwater being heated in gal/min
Q = quantity of
Q x 500 x S g x Sh x (T2 – T1)
H
Substituting intofgthe preceding equation results
in the following:
Q x (T2 – T1)
C = 25 x 500
x .93 x .47 x (225 – 65)
2
C=
912
Q xx (T
(T2 –– TT1))
Q
2
1
C
=
C
=
958
lb/hr
C = SCFM
24 x (T2 – T1)
C=
QQxx(T500
– xT1S) 900
2. Steam
air or a gas indirectly through
2heats
g x Sh x (T2 – T1)
C
=
x
D
x
C metallic
= SCFM
a
wall
4
v Sh x (T2 – T1) x 60
C=
H fg
Plain or finned heating
coils and unit space
H
Q x are
500common
x S g xfgShexamples
x (T2 – T1)
heaters
C=
H
The following formula
provides a quick and
25 x 500 x .93fgx .47 x (225 – 65)
approximate
condensate
C
= 970 x (w1 basis
– w2 ) for
+ westimating
1 x (T2 – T1)
C = for this type912
loads
of equipment.
Hfgx x.47
t x (225 – 65)
25 x 500 x .93
C = SCFM x (T2 – T1)
C = w x S x (T – T912
h
2 9001)
C=
x
t
H T)
SCFM
fgxx(T
SCFM
D2v –x formula
S1h x (T2 –will
T1) provide
x 60
A =more
detailed
a more
C
C
=
900
accurate estimate
H of condensate load:
fg
[
]
SCFM
x Shxx(T(T2 2––TT1)(1.1)
Lp x wx pDxv .12
1) x 60
H
H fgx t
970 x (w1 – wfg
– T1)
2 ) + w1 x (T+2[(.5)(C
Where:
C=
2)]
Hfg x load
t
C
= condensate
in lb/hr
970
(w
– w )T+a)wor
– T1) heated
L xx Aantity
x1Uxgas
x(TI2f being
p x1 (Tpof2– air
CSCFM=
C = w px Su
h x (T2 – T1) 3
C2 =
in standard
HHfgfg x ftt /min
fg x t H of gas in lb/ft3 (0.75 air)
Dv
= density
w x Sh x (T2 – T1)
Sh=
= s pecific heat of gas being heated
C
x t H x (T – T )(1.1)
fgBTU/lb/°F
w
LLp xin
wppxx.12
.12 x (T22 – T1 1)(1.1)
CT1 == =pixnitial
C
temperature
of gas being heated
11
HHfg xx tt
CC1 =
[
[
[
]
]
in degrees
fg
L x w x .12 x (T2 – T1of
+ [.5C
+)(1.1)
[(.5)(C
Q =25quantity
of petroleum
heated
gas
being
2 ] heated
x 500 x .93
x .47 x (225being
– 65) Page
58 in
2)]
CT12= =pfinalp temperature
Page 59
C = gal/min
Q x (Tin2 degrees
– T1)H x t
C = L x A x (T fg
x 500temperature
x .93912
x .47 x (225
– 65) being heated
Taof)xxvaporization
U x I–f 40) x 1.1
T1 =25initial
of liquid
p=2latent
px–.12
x p10.79heat
(338
+ [(.5)(C2in
)] BTU/lb
C
=
CH21 fg= 100
Page 58
SCFM
x (T2 – T912
)
in degrees
900
=
c
onstant
that
assumes
a typical
Hfg
1
881 x 149
C
=
(T –temperature
T)
2 – T1) heat, density, latent heat and
T2 =Q fxinal
of liquid being
in C = QLx x(Tspecific
Page heated
55
p Ap x (Tp – Ta) x U x If
C = SCFM2x (T12 –900
T1)
C
=
4
+ [8.95]
a conversion of minutes
to hours
degrees
2
2
C = SCFM
Hfg
x Dv x900
Sh x (T2 – T1) x 60
60
=
minutes
in
an
hour
C = Q x (T – T )
wp xx S.12
x
(T
–
T
)(1.1)
Lpx x500
Q
x
S
x
(T
–
T
)
g
h2
21
1
CC1 == 338 – 40 = 1.49
2 x D1 x H
A
detailed
formula
is appropriate when
fg
C more
= SCFM
t=
v Sh x (T2 – T1) x 60
xt
C
= liquids
4
200HHafgfgsolid
3. Steam heats
or a slurry indirectly
other
areHbeing heated:
Lp x wp x .12 x (T2 – T1)(1.1)+ [.5C ]
fg
a metallic wall
Cthrough
2
Q x 500 x S g x Sh x (T2 – T1)
1=
Page
59
xt
C = 970 x (w1 – w2 ) + w1 x (T2 – T1)
Clothing presses,Hfg
cylinder
driers for textiles or
H fg
25and
x 500
xT.47
xU(225
– 65) are typical
C=
x x(T.93
x If–plastics
paper
presses
for
pxA
p x–
a) xx (338
xpplaten
10.79
.12
40)
x 1.1
+ [.5C
Hfg) x+tw x (T – T )
C
= L100
2]
970 x (w1 – w
C
=
1
2
1
2
1 Page 59
2
The
formula shown
When:
L912below is suitable for
C=
881 x 149
x t in lb/hr Page 60
x Sh x (T2 –HTfgload
estimating the condensate loads associated
C w
= condensate
1)
SCFM
x10.79
(T2 –xT.12
C = 25 x 500
100xx1.178
40)
x–1.1
x .93 x .47 x (225 – 65)
1) x– (338
=
C
100
x
(338
40) x–3The
x+ (1
.85)
[8.95]
with
this
type
of
equipment.
constant
Q
=
quantity
of
liquid
being
heated
in
gal/min
C
=
C = w x S fgx x(Tt H– T )
Page 56
C21 =
900
h
2 912
1
881881
xof149
970 is the latent heat
vaporization at
Sg= = specific gravity of heated liquid
C
H
338 – 40 = 1.49
fg x t heat
atmospheric
steam tables,
Sh =
specific
v x Sh x (T(reference
2 – T1) x+60
[8.95]
t == SCFM x Dpressure
SCFM
x (T2 – T1)of liquid being heated in
C
200It His included because the drying
C = British
Appendix
“C”).
per pound per
Lp x wp Thermal
x .12 x (T2Units
– T1)(1.1)
fg
C1 = degree (BTU/lb/°F)
900
process
definition
338 by
– 40
= 1.49 requires that the moisture
H
t
L
x
w
x
.12
x
(T
–
T
)(1.1)
t
=
p x pheat
Dv x fg
Sofh xvaporization
(T2 2 – T1 1) x 60in BTU/lb
in the product
Hfg= =SCFM
latent
CC
200be evaporated.
1=
+ [(.5)(C2)]
L
x
A
x
500 = c onstant,Hfor
converting
gallons
per
x
t
H
p
p (Tp – Ta) x U x If
fgfg
CC2 == 970 x (w1 – w2 ) + w1 x (T2 – T1)
minute to pounds per+ hour
[(.5)(C )]
L
[
[
[
[
C2 =
Lp x Ap x (Tp – Ta) x U x If
2
fg
a liquid with a specific
gravity of .93 and a
wxp(Txof.12
x )(BTU/lb/°F)
(T2 – T1)(1.1) from 65°F to
Lxp Sxheat
specific
.47
w
–
T
C1 =
h
2
1
C
= at the
225°F
per minute.
t –gallons
Hfgof
xrate
.12
x x(T25
Lp x w
x
t
H
p
2 T1)(1.1)
fg
CAssume
a steam pressure
of 50 psi. The
1=
+ [.5C2]
x tused to convert
Hfgbe
constant 500 may
gallons
per minute to pounds per hour.
The
+ [.5C
] 58
Page
2 latent
L
x
w
x
.12
x
(T
–
T
)(1.1)
p
1 – 40) x 1.1
100psteam
x 10.79
.12psi
x2(338
= of
C
atx50
is found
in the steam
Cheat
1=
Hfg881
xDtxto149
tables100
in xAppendix
be
BTU/lb.
10.79 x .12 x (338912
– 40)
x 1.1
[
[
]
]
]
]
Page 60
Page
57
Hfg– T )the
Example:
determine
condensate
load
L
x
A
x
(T
x
U
x
I
p x (w
p –w
p ) +a w x (T f – T )
C2 = 970
1
2
1
2
1
in
that
results
from
heating
C =pounds/hour
HHfg x t
Page 60
C1 =
]
] ]
]
+ [(.5)(C2)]
+ [8.95]
881 x 149
Lp x Ap x (Tp – Ta) x U x If + [8.95]
C2 = 338 – 40 = 1.49
t=
Hfg
338 – 40200
= 1.49
t=
200
H xt
Lp x Ap x (Tp –fgTa) x U x If
CWhen:
= 100 x 1.178 x (338 – 40) x 3 x (1 – .85)
C22 = w x Sh x (T2 –LT1)
C = = condensate load in lb/hr
881
tH
fg xweight
w1 100
= initial
of –product
dried (lb)
x 1.178
x (338
40) x 3 xbeing
(1 – .85)
Cw
2 2= = final weight of product being dried (lb)
881 of product in degrees
T1 = initial temperature
Lp x wp x .12 x (T2 – T1)(1.1)
temperature of product in degrees
CT12= = final
Hfgofxvaporization
t
Hfg = latent heat
in BTU/lb
+ [(.5)(C
t = time required for drying
(hr) 2)]
[
C2 =
]
Lp x Ap x (Tp – Ta) x U x If
Hfg
34
C1 =
Lp x wp x .12 x (T2 – T1)(1.1)
Hfg x t
+ [.5C ]
e 55
e 56
e 57
e 58
ge
e 5955
ge 56
e 60
ge 57
ge 58
C=
Q x (T2 – T1)
C=
Q x 500 x S g x Sh x (T2 – T1)
C=
4
SCFM x Dv x Sh x (T2 – T1) x 60
Hfg
H fg
Yarway Industrial
steam trapping
handbook
970 x (w1 – w2 ) + w1 x (T2 – T1)
C
=
Chapter 4 - Principles of steam trap application
Hfg x t
25 x 500 x .93 x .47 x (225 – 65) Page 57
912
C=
4. Steam heats a solid through direct contact
SCFM x (T2 – T1)
This
done in a sterilizer or a
C
= is most frequently
900 an “autoclave”
steel chamber called
SCFM x Dvformula
x Sh x (Tmay
) xused
60 for
The following
2 – T1be
C
=
estimating condensate
loads when this type
Hfg
Page
of equipment is being used. It should
be 55
Page
Page 58
55
remembered that the surrounding equipment
will also create a large condensate load at
970 x (w1 – w2 ) + w1 x (T2 – T1)
startup.
The same equation may be used to
C=
Hfg x t
estimate this load.
C=
w x Sh x (T2 – T1)
fg x t
H
When:
C = condensate load in lb/hr
Lp x wp x .12 x (T2 – T1)(1.1)
Page 59
of material heated in lb
Cw1 = = weight
56
Page
56
Hfg xoft material being
Sh = specific heat
heated
+ [(.5)(C2)]
in BTU/lb/°F
T1 = initial temperature of material being
Lheated
x A x in
(Tpdegrees
– Ta) x U°F
x If
C2 = p p
T2 = final temperature
of material being
Hfg
heated in degrees °F
Hfg = latent heat of vaporization in BTU/lb
t = Lt ime
reach
final
of 57
wto
– Ttemperature
Page
pxx(T
p x .12
1)(1.1)
) x (T2heated
C1 = Qmaterial
2 – T1being
in
hr
Page
57
C=
[
]
Hfg x t
2
[.5Ccondensate
• StepQ 2x continued:
alculate +the
2]
(T2 – T1) C
C=
load to be handled
–60
Page
4
100 x 10.79 x .12protection
x (338 – 40)traps
x 1.1
[
]
C1 =
Q x 500 x S x Sh x (T2 – T1)
C = main dripg881
x 149
Steam
H service
fg
+ [8.95]
In each of the preceding conditions,
the 58
Page
58
objective has been to heat a liquid, Page
air, gas
338
–
40
=
1.49
or
steam
25 xother
500 xproduct.
.93 x .47 The
x (225
– 65) is being
t =some
C=
condensed
to
200serve a useful purpose. In
912
considering condensate formation in steam
mains,
the reverse
SCFM
x (T2 – T1IS) true. Every effort is made
= L x A xthe
toCminimize
–900Ta) x U x of
If condensate as it
p
p (Tp formation
Cis
condensate
forms because
2 =wasted heat. The
SCFM x Dv Lx Sh the
x (T2wall
– T1of
) x the
60 pipe and its
ofCheat
= loss through
Hfg – 40)
100 x 1.178
x (338
x 3 x traps
(1 – .85)
surrounding
insulation.
Steam
in steam
C2 =
Page 59
main drip service are filling a need Page
common
59 to
881
every steam system, regardless of the purpose
for which
generated.
970 xthe
(w1steam
– w2 ) is
+ wbeing
1 x (T2 – T1)
C=
Standard
formulas
exist
for
calculating
Hfg x t
condensate loads during warming or startup
w x Shfor
x (Tsteam
conditions
2 – T1) mains and also for steady
C=
running conditions.
xtH
fg
Steam main warming load
C1 =
[
Lp x wp x .12 x (T2 – T1)(1.1)
Hfg x t
]
wp = weight of pipe in lb/ft
.12 = specific heat of steel in BTU/lb/°F
L x wp x .12 x (T2 – Tof1)(1.1)
T1 = initial
pipe in degrees
C = p temperature
T21 = final temperature
Hfg x t of pipe in degrees –
use steam saturation temperature (°F)
+ [.5C2]
[
C1 = 100 x 10.79 x .12 x (338 – 40) x 1.1
881 x 149
+ [8.95]
t=
338 – 40 = 1.49
200
w x Sh x (T2 – T1)
x t H of vaporization in BTU/lb
Hfg = latentfgheat
t = time for warm up in hr
Q x (T2 – T1to
) accommodate warming
1.1
C ==Qc onstant
Lx p2(Tx2w– pTx1).12 x (T2 – T1)(1.1)
CC = of insulation
1
[
2
Q x (T – T )Hfg x t
]
2
1
Steam
load + [(.5)(C2)]
C = Q main
x (T2 –running
T1)
4
4
LQpxx500
Ap xx (T
U2x–IfT1)
S pg –x TSah) xx (T
CC2 == Q x 500
x S g x Sh x (T2 – T1)
Hfg
C=
fg
H fg
C=
When:
C2 = condensate
wp x .12
x (T
Lpxx500
25
.93load
.472in–x Tlb/hr
(225
– 65)
1)(1.1)
= length
LCC
p1 == 25
x 500ofx pipe
.93 x in
.47ftx (225 – 65)
912
x
t
H
ACp == external areafg of pipe in ft2
912
Tp =SCFM
temperature
pipe in degrees
+ [.5C2]°F
x (T2 – Tof
1)
= ambient
x (Ttemperature
T1)
TC
in degrees °F
a =SCFM
2 –900
C=
U = h100
eatxtransfer
coefficient
of steel
10.79900
x .12
x (338 – 40)
x 1.1 in
C1 = SCFM
x Dv2/°F.
x Sh Ax (T
BTU/hr/ft
value
is
frequently
2 – Tof
1) x3 60
C = SCFM x Dv x S881
x x(T149
– T1) x 60
hpipe
2in
Hfg
still air.
C = used for steel
Hfg equal to +1[8.95]
If = insulation factor
minus
insulation efficiency
338x–(w
40
=– 1.49
Hfg = 970
latent
heat
wof )vaporization
+ w x (T – Tin) BTU/lb
[
]
1
2
1
2
1
Ct == 970 x (w200
) + w x (T2 – T1)
1–w
H2fg x t 1
C=
Example: determine
Hfg xthe
t warming and running
loadswfor
of 4” schedule 40 steel pipe when
x S100’
h x (T2 – T1)
C = wfrom
) ) x U x I temperature at
raised
LpxxSAh px40°F
x(T(T2 –to
–T1Tsaturation
a
f
fg x t Hp
CC2 ==psi. Assume
100
a
warm-up
rate of 200°F/hr,
x
t
H
fg
L
a heat transfer co-efficient for steel of 3 and
insulation
85%x efficiency.
specific
100 xxof
1.178
(338 – 40) xThe
3 x (1
– .85) heat of
p wp x .12 x (T2 – T1)(1.1)
C2 = is LL.12.
xw
x .12 of
x (T4”2 –pipe
T1)(1.1)
steel
Weight
per foot is 10.79
1
p
p
C1 =
Hfg x 881
t area in square feet
pounds
and its external
H xt
[(.5)(C2)] D). The
is 1.178 (referencefgtables in +Appendix
+ [(.5)(C )]
latent heat of steam (881 BTU/lb) at2 100 psi is
L x Apsteam
x (Tp – Ta) x Uin
x If
found
C = Linp the
x A x (T – tables
T ) x U x IAppendix D.
[[
]]
Lp x Ap x (Tp – Ta) x U x If
Hfg
Hfg load (example)
Steam main warming
C22 =
L x w x .12 x (T – T )(1.1)
C1 = Lp x wp x .12 x (T2 – T1)(1.1)
C1 = p p H x t2 1
fg
Hfg x t
+ [.5C2]
+ [.5C2]
[[
C1 = 100 xx 10.79 x .12 x (338 – 40) x 1.1
.12 x (338 – 40) x 1.1
C1 = 100 10.79 x881
x 149
881 x 149
+ [8.95]
+ [8.95]
C1 = 41.3 lb/hr
338 – 40 = 1.49
t = 338 – 40 = 1.49 hr
200
t=
200
]]
Steam main running load (example)
+ [(.5)(CPage
2)] 60
Page 60
When:
Lp x Ap x (Tp – Ta) x U x If
C1 == condensate
load in lb/hr
2
Hfg in ft
Lp = length of pipe
ge 59
C=
]
Lp x Ap x (Tp – Ta) x U x If
C2 = Lp x Ap x (Tp – Ta) x U x If
L
C2 =
L
100 x 1.178 x (338 – 40) x 3 x (1 – .85)
C2 = 100 x 1.178 x (338 – 40) x 3 x (1 – .85)
C2 =
881
881
C2 = 17.9 lb/hr
Appendix A provides tables that may be used
for making estimates of the condensate load
created in insulated steel pipe at various
operating pressures.
35
Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Figure 4.5
Typical tracer condensate loads in lb/hr/100 ft of pipe and product temperature between 100°F
and 200°F, stream pressure 100 psig.
Ambient temp. °F
-20
20
60
4
4-8
3-9
2-7
8
8-14
5-15
3-12
Product pipe size, in
12
16
10-19
14-25
7-20
9-26
4-16
5-22
20
17-31
11-32
6-27
24
20-37
13-38
7-32
Assume wind velocity of 0 mph, insulation efficiency 85% and no heat transfer cement
Steam tracing service
Supplemental heat is often provided to protect
piped fluids from freezing or becoming so
viscose that handling becomes difficult or
impossible. Valves, controls and instruments
also are commonly 'traced' to assure cold
weather does not prevent their satisfactory
performance. The principles involved in
calculating the condensate loads for tracer
lines are similar to those associated with
calculating the running loads of steam mains.
Experience shows these loads to be very small,
as can be seen in Figure 4.5.
• Step 3:Select a suitable safety load factor
The safety load factor is a number. It is
based on the judgment of an individual with
experience in steam trapping and is used
in trap sizing calculations to compensate
for the lack of exact knowledge about the
condensate load a trap will actually experience.
Estimates of condensing rates in the heat
exchange equipment are rough approximations
at best. Pressure and condensate temperature
estimates are often significantly in error
because of unexpected or uncontrollable
system variances or fluctuations.
It is human nature to err on the side of
selecting overly conservative safety load
factors. It is unfortunate that the problems
resulting from oversizing take longer to
become visible than those from undersizing.
Technically the safety load factor may be defined as:
Safety load factor =
Rated capacity of steam trap
Calculated condensate load of application
36
Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Figure 4.6
Typical relationships between the heating function being performed by the steam, the type of
equipment being used, the system characteristics and a reasonable safety load factor. Reviewing
such a matrix can help form the judgment necessary to select a suitable safety load factor.
Equipment being drained
Function
Heating liquid
Type
Batch stills, shell and tube
heaters, tank coils, vats
Tilting kettle, shipboard tank
Heating air
Unit heaters, pipe coil
radiators, process air heaters
Drying or curing
Platen, chest type ironer
Cylinder dryer, paper machine
Autoclave sterilizer
Transfer steam
Main drip
to point of use
Provide auxiliary
Tracing
heating to controls
and process piping
Significant
characteristic
Gravity drainage
Safety load factor
Pressure
Constant
Variable
pressure
pressure
2
3
Syphon or lift drainage
3
4
Ambient air above
freezing
Ambient air below
freezing
Gravity drainage
Syphon drainage
Normal warm up
2
3
3
4
3
5
3
-
Fast warm up
Small condensate load
5
1*
-
Small condensate load
1*
-
* Theory would suggest that a safety load factor of (1) is bad practice. However, experience establishes that
trap manufacturers seldom design a steam trap for these light load services with a suitably small seat orifice
because it is so easily blocked with dirt or oxides in normal service.
• Step 4:Solve the equation
Condensate load (lb/hr) x Safety load factor =
Desired trap capacity (lb/hr)
The product of the calculated condensate load
and the estimated safety factor is the trap
capacity that forms the basis for choosing
a correctly sized trap.
• Step 5:
Choose a trap from the
manufacturer’s catalog
Manufacturers generally provide their sizing
capacity data in graphic form indicating the
pressure and condensate temperature at
which the rated capacity is stated to exist. As
an example, Figure 4.7 shows capacity curves
typical of a bimetallic trap having medium to
heavy capacity.
Temperatures may sometimes be stated
as “near steam temperature” or “within
10 degrees of saturation temperature.”
These generalizations result from the fact that
obtaining very accurate data is difficult even
in a well equipped laboratory because of the
difficulty in providing sufficient amounts of
condensate at constant temperature. “Cold
water” ratings are sometimes stated because
they are easiest to obtain and because they
give an indication of a trap’s capacity during
a startup situation.
Choose a trap with a capacity close to
the calculated capacity for the pressure
conditions and, of course, the proper sized
end connections. Remember that while the
calculated load can be carried out to the
second decimal place, it is at best a rough
approximation and that unexpected system
variables may upset an otherwise good
selection.
37
Yarway Industrial steam trapping handbook
Chapter 4 - Principles of steam trap application
Yarway Model 40
Figure 4.7
Steam trap capacity
Differential, pressure, bar
0.1
0.2
0.3
0.5
1
2
3
5
10
20
30
5000
10,000
9,000
8,000
7,000
6,000
5,000
4,000
3000
d
Col
3,000
°F
, 70
ter
wa
2000
Discharge, lb/hr
700
1,000
900
800
700
600
500
400
500
re
mperatu
team te
, near s
te
a
s
n
e
d
Hot con
300
200
Discharge, kg/hr
1000
2,000
300
100
200
70
50
100
80
30
60
1
2
3
4 5 6 7 8 9 10
20
30 40 50 60
80 100
200
300 400 500 600
Differential, pressure, psi
Summary
Steam trap application is the process of first,
sizing it to meet the specific condensate
drainage requirements of a particular piece
of equipment, and second, selecting a type
of steam trap.
• Steam trap sizing is the process of matching
the condensate drainage requirements of a
particular piece of equipment with a steam
trap’s condensate handling capacity at the
pressure and temperature conditions to
which it will be exposed.
Standard formulas exist to calculate the
condensate loads that process traps will
experience when serving any of the following
four classes of equipment:
• Heats a liquid indirectly through a metal wall.
• Heats air or a gas indirectly through a metal
wall.
• Heats a solid or slurry indirectly through a
metal wall.
• Heats a solid through direct contact.
Condensate loads experienced by protection
traps in tracer and steam main drip service
can also be calculated by the use of standard
formulas. These loads are generally quite small
and experience has shown that trap oversizing
is a common problem.
Calculated condensate loads for process
traps are normally increased by a safety load
factor to compensate for system unknowns.
Guidelines exist to aid in the selection of safety
load factors. In general, the more that is
known about the conditions associated with an
application, the smaller will be the size of the
factor.
• Steam trap selection is the process of
evaluating the relative advantages and
disadvantages associated with each of
the basic trap technologies (thermostatic,
thermodynamic and mechanical), and
matching them with the needs or criteria
of the plant in which they will be used.
These needs, or selection criteria, create
a surprisingly long list:
• Safety
• Efficiency
• Service life
• Ease of checking
• Sensitivity to back pressure
• Resistance to freeze damage
• Dirt sensitivity
• Installation versatility
• Air venting
• Responsiveness to changing loads
• Resistance to shock, vibration and water
hammer
• Predominant failure mode
• Discharge mode
• Condensate discharge temperature relative
to saturation curve
• Magnitude of condensate subcooling
• Ease of maintenance
• Supplementing accessories or features
• Commercial considerations
Selection of a thermostatic, thermodynamic
or a mechanical type trap for a particular
service will necessarily depend on the criteria
considered most important for satisfactory
plant operation, as each trap technology has
its unique advantages and disadvantages.
38
Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
Chapter 5 – Introduction
A steam trap that fails to perform as expected
is not necessarily faulty. Often 'trap problems'
are directly traceable to 'piping system
problems'. There are general piping system
practices that must be followed if certain basic
steam trapping problems are to be avoided.
While some pieces of heat exchange equipment
have rather special piping requirements to
achieve good trap performance, most do not.
This chapter addresses the generalized rules
for good piping practice and proper steam trap
installation. Recommendations for trapping
specific pieces of equipment are described
in Appendix A.
A review of the problems affecting steam
trap performance
'Good practice' evolves as knowledge is
gained about the cause of problems and the
techniques that are developed to avoid their
repetition in the future. As background to
a consideration of steam trap installation
principles, it is helpful to review the most
common problems associated with trap
performance:
Problems:
• Water hammer
Comment: slugs of water hurtling through a
piping system not only damage steam traps,
but also other valuable equipment including
the piping system itself. Good piping practices
promote good drainage and prevent the
accumulation of water that makes water
hammer possible.
• Freeze-ups
Comment: a shutdown in freezing conditions
of a system that drains poorly, for whatever
reason, is an invitation to trouble. In
extremely cold conditions, poorly insulated
condensate return systems can freeze. Even
if equipment is not damaged by ice, seldom
the case, startups become extremely tedious
because ice blockages prevent the circulation
of steam necessary to bring the system up to
temperature. Valuable production time is lost.
Yarway Model 515
• Dirt
Comment: by their nature, steam traps
generally have small passages that are
subject to obstruction. Corrosion products
and pipeline trash are the usual culprits. A
clogged steam trap means trouble because
it is no longer able to protect or drain the
equipment it was meant to serve. Dirt pockets
and strainers help to protect the trap.
• Air binding
Comment: at startup time, steam systems
can be full of air. Some mechanical and
thermodynamic traps have difficulty
differentiating between steam and air. When
such traps restrict the proper venting of
air and delay the heating up of the system,
they are considered to be 'air binding'.
Thermostatic air vents and thermostatic traps
are commonly used to improve air venting.
• Steam binding
Comment: certain applications, piping
configurations and steam trap types tend
to create conditions in which steam at the
trap keeps it closed, thereby preventing
condensate which has formed upstream
of the trap from being drained.
• Back pressure
Comment: small levels of back pressure
typical of a properly designed condensate
return system are not generally a problem.
It is the elevated levels of back pressure
found in the inadequate return system that
creates drainage problems.
• Corrosion
Comment: corrosion is best controlled
by proper boiler water treatment but any
piping arrangements that interfere with
good drainage increases the potential for
corrosion problems.
39
Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
The steam trap station – some basics
Figure 5.1 shows a typical steam trap
installation in a closed condensate return
system.
Several of its features will apply to any
installation, specifically:
• Strainers with blowdown valves: dirt is
the enemy and unless a steam trap has
an integral strainer, as many now do, it
should have a strainer installed immediately
upstream. The blowdown valve which permits
easy cleaning of the strainer screen often
sees service as a useful diagnostic tool when
a system or piece of equipment is slow to
heat up.
• Test 'T': regular verification that a steam trap
is functioning properly is common practice in
all well maintained plants. Chapter 6, Steam
trap maintenance, has a section on steam
trap checking that describes the usefulness
of a test 'T' for verifying proper performance
of a trap discharging into a closed return
system.
• Isolation valves: isolation valves are
necessary to permit the inevitable repair or
replacement that all steam traps ultimately
require. They are also required when using
the test 'T'. Valves should be fully ported –
such as ball or gate valves – to minimize
pressure drops that cause condensate
flashing or raise back pressures.
Steam trap location – the inlet piping and
outlet piping
Steam traps should be installed one or two feet
below the outlet of the equipment being served
with the inlet piping sloping towards the trap to
facilitate gravity drainage. A drip or dirt leg that
is the same size pipe as the equipment drain
connection will help provide clean condensate
and also serve as a condensate collecting
reservoir. Pipe and fittings ahead of the trap
should be equal to or one size larger than the
trap to reduce the potential for the formation of
flow interrupting flash steam. Discharge piping
should be amply sized to accommodate flash
steam and minimize back pressure. For short
discharge lines, use pipe equal to trap size; for
longer lines use one pipe size larger.
When it is not possible to install a trap below
the low point of the equipment being drained, a
lift fitting or water seal is necessary. This may
take the form of either a 'U' shaped lift fitting or
a small pipe or tube within the larger coil (see
Figure 5.2).
Without such an arrangement, steam is able
to reach the trap and keep it closed (steam
binding) before the coils have been adequately
drained. The trap should be located below the
high point of the loop going over the side of the
tank. A check valve is installed just ahead of
the trap to prevent back flow into the coil.
Figure 5.1
A typical steam trap installation
Overhead return line
Branch line
Valve
Steam
equipment
Steam main
Drip trap
Dirt
pocket
Strainer and
blowdown valve
Strainer
Trap
Union
Tee
Check
valve
Blowdown
valve
Return line
Figure 5.2
A lift fitting application
Steam line
To return
Swing check
valve
Process
liquid
Slope
Small pipe
Steam
Large coil
To return
Condensate
40
Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
The steam distribution system drainage and
trapping
Good drainage of steam mains and branch
lines is mandatory. A piping system that sags
or otherwise allows pockets of condensate to
form, creates the conditions that cause water
hammer and its associated damage. Such
systems when shut down in freezing climates
experience additional problems because of
unwanted ice formation. All natural drainage
points arid low points in a steam line or main
require a steam trap and, in fact, steam
main drip service is the most common trap
application. Where long pipe runs exist without
natural drainage points, they need to be created
in the form of drip pockets at intervals of
approximately 300 feet. Drip pockets should be
the same diameter as the main or branch line
as this helps prevent condensate from being
carried past the pocket by high velocity steam.
Drip pockets and drip traps should be placed
upstream of temperature control, pressure
reducing, and stop valves to prevent damage
and assure dry steam supply to equipment.
Drip traps are also required at expansion
joints and loops and the terminal ends of
steam mains.
The steam main itself should have a slope
of about one inch in twenty feet to facilitate
condensate drainage by gravity.
Steam supply lines should always be tapped off
the top of the steam main. This helps deliver
dry steam to the equipment (see Figure 5.1).
Steam separators
Separators perform a job that steam traps
cannot do. Steam traps drain condensate
that has collected at a drainage point. Steam
separators (or steam dryers) remove water
droplets that are entrained in the steam
flow. They are installed in the steam main
immediately down-stream of the boiler, to
improve the quality of steam going into the
distribution system, or immediately ahead of
equipment that requires especially dry steam.
Steam separators, in turn, are drained by a
steam trap.
The condensate return system
The primary purpose of a condensate return
system is to save the expense of continually
upgrading water to a quality suitable for good
boiler performance and to recover heat energy
still in the condensate, thus improving overall
system efficiency. In addition, condensate
return systems afford the opportunity to use
flash steam in progressively lower pressure
heating systems. Condensate return is
discussed in detail in Chapter 7.
While the benefits of a return system
significantly outweigh the problems associated
with it, such a system does allow the
formation of a back pressure against which
steam traps must discharge. Back pressure
at moderate levels is not a problem but at
levels of 50% or more of inlet pressure, it can
adversely affect the performance of bimetallic
and thermodynamic traps. The discharge
temperature of bimetallic traps become
extremely suppressed, creating significant
condensate backup. Thermodynamic traps
become less efficient i.e., begin to pass steam.
The significance of these comments is simply
to establish that piping factors which increase
the back pressure against which a trap must
discharge, also increase the potential for
unexpected trapping problems.
A common cause of excessively elevated back
pressures in a return system is the plant
expansion that increased the number of steam
traps discharging into the system without also
having increased its size to accommodate the
additional flash steam.
Figure 5.3
A condensate return system showing the collection and use of low pressure flash steam
Low pressure flash steam
High pressure
condensate from traps
Drip traps
H-P flash
tank
Atmospheric vent
Low pressure
condensate
from traps
Condensate
pump
Carefully size and
select condensate
pumps and controls
To boiler-feed system
Atmospheric
receiver
Condensate pump
41
Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
Condensate lifting
When the condensate discharged from a steam
trap must be raised to a collecting manifold
or header, it is necessary to assure that the
discharge pressure at the trap is sufficient to
overcome the vertical lift plus the pressure
in the overhead return line. If this is not the
case, reverse flow will take place. Every foot
of elevation following a trap will add ½ psi
to the back pressure the trap experiences.
It is important to assure in these applications
that total back pressure does not exceed the
allowable limits of the particular type of trap
selected. Figure 5.4 shows an example of the
arithmetic used in estimating back pressure
when a trap is discharging to an overhead
return line. Note that pipe, valves and fitting
pressure losses will also contribute to the back
pressure.
In the example shown, a check valve is installed
at the bottom of the riser. This is to prevent
backflow into the heating coils and encouraging
corrosion when the system is shut down. Check
valves tend to leak over time and hence, in
this example, would be effective only during
relatively brief periods.
Pumping traps
The installation shown in Figure 5.4 is
representative of many situations in which
condensate is raised to an overhead return
main by pressure in the discharge line. There
are occasions when this type of drainage
arrangement is not considered especially
satisfactory. An alternative approach employs
a device called a 'pumping' trap. This has
the advantage of allowing a number of traps
to drain condensate by gravity to a sump
before being raised to the return main.
Water hammer potential is reduced and quicker
plant startups are possible when pumping
traps are used. Pumping traps also can lift
condensate from a condenser or turbine drain
that may be operating at vacuum conditions.
The principle of a pumping trap is that of
a closed receiver fed and drained through
check valves. It contains a float that rises
until it opens a valve admitting steam that
pressurizes the receiver. This, in turn, forces
the accumulated condensate out of the receiver
to an elevated return system. The falling float
closes the valve admitting steam and opens an
atmospheric vent. Condensate can now flow
again by gravity into the unpressurized receiver
until the float again rises sufficiently to repeat
the pressurizing cycle.
Auxiliary air vents
Air in a heating system significantly reduces its
efficiency. Air is a very poor conductor of heat
and air filming on pipes and heat exchanger
tubes reduces the heat transfer rate through
their metal walls. Also, steam mixed with air
contains fewer BTUs at a given pressure than
steam alone. It is the function of a steam trap
to aid in venting air from a steam system,
but auxiliary thermostatic air vents are often
required. Open to cooler air and closed to
hotter steam, they greatly speed up the air
purging process. When frequent startups
and shutdowns are the rule, rapid air purging
is a significant factor. Thermostatic traps
are often favored for their good air handling
characteristics on startup. Figure 5.5 shows
schematically a typical autoclave installation
with auxiliary air venting.
Figure 5.4
Estimating back pressure when discharging to an overhead return
Steam in
5 psi
condensate
return
Control
valve
6 ft
Swing
check
valve
Trap
Sufficient length to
prevent coil corrosion
and/or freezing
½ psi per foot
creates 3 psi
Pipe flooded with
condensate
3 psi + 5 psi = 8 psi
Total back pressure
Dirt pocket
42
Yarway Industrial steam trapping handbook
Chapter 5 - Principles of steam trap installation
Vacuum breakers
When a closed and pressurized steam system
is allowed to cool down, it is not just the
temperature that drops. The pressure in the
system will decay to a vacuum unless some
mechanism permits the entrance of air, thus
allowing the system to achieve atmospheric
pressure. Such a mechanism is called a
vacuum breaker. It is essentially a check valve,
closed to internal pressure, but open when
that internal pressure becomes less than
atmospheric. Figure 5.6 shows schematically
the installation of a vacuum breaker on an air
heating coil.
If the upper shut-off valve is closed while the
heating unit is in operation, condensate will
not be able to drain out of the unit.
As it cools, it is possible for condensate that has
drained, into the return system earlier, to be
drawn back into the unit unless a vacuum breaker
functions to permit air to enter the system.
Figure 5.5
Auxiliary air vents are often helpful in purging
air from large steam spaces at startup
Yarway Model 71I
Figure 5.6
A vacuum breaker aids in the drainage of condensate when a steam system is shut down
Vacuum breaker
Steam in
Steam line
VB
Auxiliary
air vent
A
Air heating coil
A Air vent
Autoclave
Air
Min. as recommended
by coil mfgr. up to 3 ft for
modulating steam and
freezing air temperature
Trap
Condensate return
Summary
Performance problems with steam traps
are often directly traceable to the piping
arrangements used to install them. Experience
continues to justify the wisdom of knowing and
following good piping practice.
Ideally, condensate should be able to drain
freely to (and from) a steam trap by gravity.
Line restrictions which may produce elevated
back pressures or lead to condensate flashing,
should be avoided. Such restrictions may result
from the use of undersized valving or excessive
pipeline size reductions. When condensate
must be raised to reach a trap or an elevated
return main, care should be exercised so that
steam binding or excessive back pressures
do not occur.
Steam traps should be installed so that
performance checks and maintenance activities
can be easily performed. Properly sized
strainers with a suitable blowdown valve are
an easily justified steam trap protection device.
Air vents, vacuum breakers and check valves
may be required to solve specific drainage or
flow problems which otherwise would adversely
affect a steam trap’s performance.
The removal of condensate from a steam
system cannot be considered as an
afterthought. The absence of problems
associated with water hammer, corrosion, dirt
and freeze-ups has been the result of careful
planning and conscious effort to avoid the
root causes of these problems.
43
Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Chapter 6 – Introduction
Steam traps must be selected, sized and
installed carefully if good system efficiencies
are to be achieved. By themselves, however,
these factors will not assure an efficient
system. In the long run, regular maintenance of
the selected traps will be the significant factor
in system efficiency because in time all steam
traps fail. In spite of the certainty of failure and
the high cost consequences that can result,
really good trap maintenance programs seem
to be the exception rather than the rule. This
may be because traps are relatively inexpensive
devices and it may be wrongly considered that
they perform a relatively inconsequential task.
The equipment that traps protect is often
large and expensive. Its damage or reduced
productivity can be very costly. When a steam
trap fails in the closed position, condensate will
back up into a heat exchanger. This can spoil
the product at the worst or simply reduce heat
exchanger utility at the best. A trap that has
failed closed in other circumstances, such as in
a freezing environment, can readily lead to lines
blocked or broken by ice.
Alternatively, when a steam trap fails in its open
position, it usually damages nothing. It simply
allows steam to flow through a system at much
higher rates than is necessary for the heating
job to be performed.
It reduces system efficiency in the same
manner as any other steam leak. While it is
generally considered more desirable for a
trap to fail in the open rather than the closed
position, either can have significant adverse
cost consequences.
The very high cost of generating steam, and
then failing to use it properly, is beginning
to gain the attention of plant managers.
Also, recognition is developing that a good
steam trap maintenance program is not
a questionable expense but a source of
significant cost savings both in fuel costs
and in higher equipment utilization. Any plant
seriously interested in reducing its energy
costs must develop a systematic approach
to maintaining its steam traps in proper
operating condition:
Maintenance programs
Maintenance programs will necessarily differ
among plants having five, five hundred or
fifteen thousand steam traps. Nevertheless,
their objective will be fundamentally the same.
In larger plants having one thousand or more
traps, individuals with the full-time assignment
of checking and reporting the performance of
steam traps are increasingly common. Smaller
plants may not have a full-time specialist, but
some are attempting to have an individual
who is especially knowledgeable about
steam traps and steam-trapping practice.
Regardless of the size of the plant; a common
problem exists for every steam trap user: the
difficulty of determining if a trap is working
properly. While sometimes it is a relatively easy
matter, frequently it is difficult, speculative
and uncertain. Specialized equipment exists to
help the steam trap checker and a great deal
has been written listing logical progressions
of questions and tests to establish if a trap is
performing properly for its given conditions.
However, conclusive answers to some of these
questions are frequently not easy to supply.
To date a good bit of experience, judgment and
art are still necessary to identify malfunctioning
traps – especially if they are discharging into a
closed return system.
• Numbering and tagging every trap location
is essential for a successful maintenance
program. The written records of the condition
of each trap at the time of inspection are
also essential so that inspection frequencies
can be logically established. These records
also provide opportunities for a wide range
of performance analyses and comparisons
between trap types should there be evidence
that additional cost savings can be obtained
by seeking absolutely optimum performance.
The essentials of a successful maintenance
program
Successful maintenance programs of the
larger users of steam traps tend to have certain
common elements. A review of these elements
can be useful to maintenance managers in
the plants having small as well as large trap
populations. They are:
• A committed member of Plant Management
who understands the high financial
payback associated with an efficient and
well-maintained steam trapping system.
• A valid cost analysis developed over a
meaningful period of time which has shown
the dollar savings in energy costs associated
with a specialized pilot maintenance program
for steam traps. Often initiated in a single
portion of the plant, these pilot programs,
allow product produced to be correlated
with steam consumed both before and
after the start of a specialized steam trap
maintenance activity.
• A full time steam traps maintenance crew,
including a diagnostic specialist, in addition to
the personnel who repair or replace defective
traps.
• A set of steam trapping standards which
recommend a correct piping configuration
and trap type for the various trap applications
in the plant. Efforts generally have been
made to standardize on as few trap types
as practical.
• A complete, but easily kept, set of
maintenance records including simple
maps identifying the location of every trap
in each area of the plant. Survey sheets are
employed that list (1) an identifying number
for every trap location in a given area; (2) the
equipment being drained; (3) the operating
pressure; (4) the trap type suitable for the
application; (5) and a place to record trap
condition at the time of a survey.
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
The importance of trapping standards
When experience has shown that the
requirements of a certain application are well
satisfied by a specific type of trap and piping
configuration, it makes sense to establish a
trapping standard that will apply to all similar
applications. When this standardizing process
is expanded to cover all trap applications in
a plant, it produces important benefits. The
steam trap maintenance activity is greatly
simplified. The variety of traps in use is reduced
and their proper performance becomes better
understood by maintenance personnel. Traps
that have reached the end of their normal
service life are repaired. Misapplied traps
are more easily recognized and are replaced,
rather than mistakenly reinstalled. Repeatedly,
the experience of steam trap users who make
the effort to standardize their steam trapping
practices is an improvement in system
reliability and efficiency.
Establishing trapping standards
A plant that has become convinced it can
benefit from the establishment of steam
trapping standards may be tempted to simply
adopt standards which have been successfully
used elsewhere. This is probably unwise. A
chemical plant, a refinery, a papermill or a food
processing plant reasonably can be expected to
have different trapping standards. The manner
in which these plants operate will be different
and their exposure to freezing weather can
vary – both factors will strongly influence the
standards that should be adopted. While good
piping and installation practices are the same,
regardless of industry or climate, the specific
trapping requirements of individual plants
should be recognized.
Getting started with trapping standards
The initiation and development of trapping
standards for an organization may occur in a
wide variety of ways, but ultimately someone
has to wrestle with some basic questions.
Typically:
1. How should steam trap applications be
classified so that standardization can
reasonably take place?
2. What are the most important criteria by
which steam trap performance should
be judged?
Classification of steam trap applications
Steam trap applications are classified in at
least two major ways:
1.Type of equipment being drained. For
example; steam mains, drying cylinders,
heat exchangers, storage tanks, vulcanizing
presses, tracing lines.
2.By generic conditions as defined by
pressure and condensate load. These can
be represented by a simple matrix such
as Figure 6.1 or one that is more refined,
Figure 4.2.
If the operating conditions – i.e., pressure and
condensate loads – are quite uniform for each
of the specific types of equipment in a plant,
then classification by equipment being served
may be quite suitable. Often this is not the case;
as there may be steam mains at 100 psi and
others at, say 500 psi, or small heat exchangers
having condensate loads of 1000 psi while
others approach 10,000 psi. Differences of
these magnitudes almost inevitably lead to
different standards recommendations. Generic
classification of operating conditions by its very
nature tends to be more widely applicable.
Sometimes it is portrayed in a graphic manner
as shown in Figure 6.2.
Figure 6.1
Matrix format that can be helpful in establishing plant-wide steam trap standards.
Each quadrant block should reference the preferred type of trap for the stated conditions.
Diff. pres.
Below 100 psi
Between 100 and 300 psi
Between 300 and 600 psi
Below 100 lb/hr
Load
Between 100 and
1000 lb/hr
Between 1000 and
10,000 lb/hr
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Trap evaluation criteria
A list of the criteria useful in evaluating the
suitability of a steam trap for a particular
application can be quite long. Chapter 4
'Principles of steam trap application' discusses
these criteria at length and Figure 4.3 shows
such a list. Selecting a steam trap type
(thermostatic, thermodynamic or mechanical)
as the standard for a particular application
in a plant requires making decisions about
the inherent advantages and disadvantages
associated with each type. Chapter 3 'Operating
principles of steam traps' describes these
advantages and disadvantages. Obviously, the
decision to standardize on a particular trap type
for a certain application should be made with
great care and after evaluation of all relevant
factors because, by definition and intent, a
standard will be used over and over again.
Steam trap checking
Regardless of the care that has been spent in
classifying a plant’s steam trap installations,
and the thoroughness with which various
types of traps have been evaluated and the
care with which plant standards have been
prepared, there will ultimately be the need
to judge whether the installed traps are
working properly or whether they require
repair or replacement. This is not a job for
the untrained and inexperienced.
Certain gross failures are of course readily
detectable. A cold steam trap is obviously not
working although it remains to be determined
whether the trap has failed mechanically,
or whether accumulated dirt and scale has
choked flow through the trap, or whether it has
been inadvertently valved out of service as a
result of some unrelated maintenance activity.
Traps that are visibly leaking steam at joints or
seals have clearly failed. Traps conspicuously
blowing large amounts of vapor from their
exposed discharge side probably have failed,
but it is at this point that a level of uncertainty
begins to develop. Most properly operating
traps will have 'flash steam' associated with
their discharge. In addition, the amount of
vapor and the pattern of discharge (continuous
or cyclic) of a properly operating trap are
significantly influenced by normal operating
variables such as pressure and condensate
load. Uncertainty increases in a dramatic
fashion with attempts to assess a trap’s
performance when it is discharging into a
closed return system and it is not possible to
see its discharge pattern.
Despite these areas of uncertainty, learning to
identify grossly failed steam traps can proceed
with a reasonable level of confidence. However,
it is the ability to identify that a trap has started
to fail and is beginning to pass more steam
than is acceptable (but has yet to reveal itself
as a grossly failed trap) that elevates steam
trap checking to a task for a skilled and
knowledgeable individual.
Figure 6.2
Example of a graphic format that can be helpful in establishing plant-wide steam-trap standards.
Equipment having operating conditions defined by one of the reference areas should be able to
utilize successfully a given trap type and installation layout.
10,000
Reference D
Condensate load lb/hr
1,500
1,000
Reference C
150
100
Reference A
Reference B
50
10
0
100
200
300
400
500
600
Pressure, psi (trap inlet, minus trap outlet)
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
A basic rule (with no exceptions)
It is essential that anyone assigned the
responsibility of checking steam traps
understand the principles of operation of the
various types of devices to be checked.
It is no more realistic to attempt to diagnose
the performance of a steam trap without
first knowing its principle of operation than it
would be to diagnose the performance of an
internal combustion engine without knowing
the difference between a diesel, turbine, or
gasoline engine.
Chapter 3 'Operating principles of steam
traps' describes how each of the various
trap technologies work. Thermostatic traps
(bimetallic, filled bellows, diaphragm capsule
and constant temperature-capsule) all
have different performance characteristics.
Thermodynamic traps (disc, piston, lever) have
different performance characteristics between
themselves and also from the thermostatic
models. Mechanical traps (bucket and float)
have performance characteristics that differ
from each other and yet are similar to some of
the other trap types.
In summary, it is essential to know the
principles of operation of a trap before
attempting to check its performance. It is
also important to be aware of a complicating
factor: the 'usual' performance characteristic
associated with some trap types can be altered
significantly under certain operating conditions.
This phenomenon is generally associated with
very high or low condensate loads (relative
to the trap’s capacity) or with very high or
low pressure differentials across the trap
(relative to its pressure rating).
Fundamentals concerning trap failures
• Most types of traps will fail open so that they
leak steam. Some types of traps fail closed so
that they pass neither condensate nor steam,
and some types of traps will fail unpredictably
in either an open or closed mode.
• All types of steam traps can appear to have
failed because of some shortcoming or
problem in the system in which they are
installed. While this fact must always be kept
in mind it does not become a significant issue
unless the steam system has been neglected.
• The most common failure for all types of
steam traps is erosion of the seat and valve
sealing faces. This keeps the trap from
closing tightly. Once a small leak starts in
a pressurized steam system, it becomes a
large and expensive leak in a short time.
Seat and valve leakage generally results
from pipeline dirt becoming caught between
their mating surfaces. Small manufacturing
imperfections relating to surface finishes or
proper alignment can also shorten trap life.
• Pipeline dirt, oxides, scale and pipe joint
sealants are the enemy of all types of steam
traps. Some trap types are more forgiving
than others, but all have their limits. A trap
which has the appearance of having failed
closed because of dirt can often be restored
to useful service with a simple cleaning.
A trap leaking steam because of dirt between
the valve and seat probably should be
replaced or repaired with new components.
The likelihood of permanent damage having
occurred because of the dirt is high.
• The life expectancy of a trap is largely related
to the pressure at which it must operate.
In general – the higher the pressure, the
shorter the life.
Fundamentals concerning trap checking
techniques
Checking a steam trap is the process of
observing its performance and comparing it
with the performance characteristics that one
has learned are typical for a healthy trap of the
same type. If the performances are similar,
the trap may be judged to be O.K. If there are
differences, it can be concluded that either the
trap is faulty or the system in which the trap is
installed has a problem.
There are three basic techniques used in
observing the performance characteristics of
a steam trap. They are:
• Sight: visually observe the discharge pattern.
• Sound: listen to the functioning of the valve
mechanism and the flow of fluid through
the seat.
• Temperature: determine the trap’s
temperature.
Each of the checking techniques has its
limitations and seldom can a conclusive opinion
be reached on the basis of a single type of
observation. Experienced steam trap checkers
invariably try to use all three techniques. Some
will use more expensive checking equipment
than others in this checking process, but
the quality of their results does not seem
to vary much.
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Sight
Watching the discharge pattern of a steam
trap is probably the most reliable method of
determining whether it is working properly.
Unfortunately, many traps discharge into closed
condensate return systems without test 'T's and
the discharge pattern is not visible. Under these
conditions trap performance appraisal is limited
to sound and temperature monitoring.
The fundamental limitation to observing the
discharge pattern of a steam trap in order
to assess its health is that hot condensate
discharging to atmosphere flashes into steam.
The observer then has to decide whether the
clouds of vapor being witnessed are the result
of leaking steam or the normally expected
flash steam. An experienced eye begins
to distinguish the lazier action and white
appearance of flash steam from the more
transparent jet-like discharge of live steam that
can be seen right at the trap’s outlet. The best
clues come with watching a steam trap that
has a normal crisp off/on cycle, such as a disc
or bucket trap. If the discharge vapor has any
velocity during the closed period of the trap’s
cycle, it can be reasonably assumed that it is
leaking steam and should be replaced.
While most thermostatic traps can have a cyclic
mode discharge, it tends to be slower and less
definite than either the disc or bucket types.
Thermostatic traps, especially bimetallic traps,
can also have a continuous discharge pattern.
Float traps that are designed for continuous
modulating drainage are harder to diagnose,
especially in the early stages of failure.
Steam trap manufacturers recommend,
and many users routinely install, a test 'tee'
and valving arrangement that will permit
witnessing a trap’s discharge pattern in an
otherwise closed condensate return system.
The initial extra cost of this type of installation
is handsomely repaid by the surer knowledge it
produces concerning steam trapping efficiency.
Sound
Listening to the sound of a steam trap
functioning with the bit of a long handled
screwdriver (held against the trap and
its handle pressed against an ear)
can provide important information as
to whether it is doing its job properly.
Because of the high background noise that
often surrounds a steam trap, the screwdriver
or industrial stethoscope is giving way to the
ultrasonic listening device with earphones.
These help to screen out the normal
ambient background noise and permit more
precise identification of a noise pattern in an
individual trap.
The weakness of these devices, which is not
overcome with the more expensive models, is
that to hear a noise pattern is not necessarily
the same thing as understanding what it
means. Listening to a trap which is designed
to have an open and closed cycle action can
quickly reveal if the trap is operating in this
manner. It can also reveal if there is any
significant leakage past the valve when it is in
its closed position. But the value of listening to
float traps or thermostatic traps operating in
a modulating mode in an effort to determine
if they are leaking steam is questionable. The
noise patterns generated in the trap can be
heard relatively easily. The problem is in the
mind of the listener – “What do they mean?”
Temperature
Every individual who checks steam trap
performance employs some sort of
temperature sensing means. A wet finger
(obviously dangerous), a squirt bottle, a
surface-contacting pyrometer, or an infrared
sensor all have the same initial objective: Is
this trap hot? If not, it can be deduced that little
or nothing is flowing through it and the trap
is not performing one of its major functions –
draining condensate. This does not necessarily
mean that the trap has failed. It first must be
determined if some obstruction either up or
downstream of the trap has blocked flow in the
pipe. Once that issue is resolved, it is logical
to proceed with steps investigating the trap
for blockage by pipeline dirt or failure of its
internal mechanism.
When it has been determined that a steam
trap is hot, the next question is whether it is
as hot as it should be. Steam traps designed
to discharge condensate very close to steam
temperature such as disc, bucket or float traps
will have a surface temperature about 5 to 10%
below the temperature of steam in the system.
Figure 6.3 shows typical pipeline surface
temperatures.
Figure 6.3
Pipe surface temperature vs. steam pressures
Steam pressure
(psig)
15
50
100
150
200
450
Steam temperature
(°F)
250
298
338
366
388
460
Pipe surface temperature range
(°F)
238 - 225
283 - 268
321 - 304
348 - 329
369 - 349
437 - 414
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Figure 6.4
Live steam and flash steam
Figure 6.5
Steam trap checking decision tree
Equipment
• Temperature measuring
• Sound detection
• Safety glasses
Knowledge
• Of basic system
• Of trap operation
Any trap to
be checked
Is it hot?
No
Yes
Is the system shut-off, blocked
with air or dirt?
What type of trap?
Thermodynamic
• Disc
• Piston
• Lever
Thermostatic
• Bellows
• Bimetal
• Diaphragm
• Constant temp.
(wax cap)
Mechanical
• Bucket
• Float
thermostatic
Yes
No
Correct
problem
Maybe
faulty trap
Proceed to section describing specific trap type
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Unfortunately, it does not follow that if
temperatures are observed in this range that
the trap is healthy. It only means it is doing half
its job properly, i.e., draining hot condensate. It
is difficult to determine by temperature alone
if a trap is leaking steam when it is designed
to operate at close to steam temperatures. If
measured temperatures are much below the
expected range, the trap can be suspected of
backing up more condensate than normal.
Traps designed to discharge condensate at
temperatures well below that of steam, such
as some of the thermostatic types simply
reverse the generalities described above.
If they measure hotter than expected; they
probably have failed and are leaking steam.
If the temperatures are well below the steam
temperatures in the system, these traps may
be judged to be backing up condensates as
they have been designed to do.
In general, there will be a significant difference
in temperatures between that observed
upstream of a trap and that observed
downstream. These temperatures will be
directly related to the pressure in the system at
the point of measurement. If the temperatures
measured up and downstream of a trap are the
same, it can only be deduced that the pressure
on either side of the trap is the same. As this
is an abnormal condition, it can be concluded
that a system problem exists that may or may
not be caused by a faulty trap discharging into
a common return. More analysis is necessary.
In attempting to answer these basic questions,
it is assumed that visual, temperature and
listening techniques will all be used. It is
also assumed that the individuals doing the
checking will have certain basic background
information about:
1.The system in which the trap is installed.
Specifically,
•T
he approximate pressure upstream and
downstream of the trap.
•T
hat the overall system is stable neither
starting up nor being shut down; the trap
application and its general characteristics.
2.The basic operating principle of the trap
and whether it can be expected to:
•D
ischarge condensate within about
10° of steam temperature as most
thermodynamic and mechanical traps
do or at much larger suppression
temperatures as is characteristic of
some of the thermostatic traps.
•H
ave a distinct off-on cycle typical
of a thermodynamic (disc type) and
mechanical (bucket) or have a modulating
or continuous flow typical of a mechanical
(float) and some thermostatic traps which
tend to throttle flow.
Figure 6.5 outlines the first major branches
of the steam trap checking decision tree.
Successive branches associated with each
trap type are presented on subsequent pages.
The trap checking decision tree
There is a logical progression of steps leading
to the decision that determines whether
an installed steam trap is healthy enough
to continue in service or whether it should
be repaired or replaced. Because of the
multiplicity of variables and the increasingly
wide variety of trap types, this decision tree can
be enormous. Outlined below is a progression
of basic questions which illustrates only the
major branches of the tree. It is suitable as
a troubleshooting starting point and entirely
adequate for identifying the vast majority of
failed traps.
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Checking thermodynamic traps (disc, piston and lever traps)
Disc traps – mechanical failure mode
• Disc traps fail in the open position. Seating surfaces wear and erode to the point they can no
longer shut tightly.
Hot disc trap
Using listening device or by witnessing
discharge, determine number of open/close
cycles per minute.
1.Disc traps may cycle up to 50 times a
minute without wasting steam. The higher
the cycle rate, the closer the trap is to the
end of its useful life. Cycles in excess of 1a
second indicate a worn out trap unless it
is experiencing an exceptionally high back
pressure. It is advisable to consider repair
or replacement of the trap when it cycles
20 to 30 cycles per minute. The trap should
open and close crisply with no leakage in
the closed mode.
2. If cycling cannot be detected with a listening
device and discharge is not visible, close
downstream block valve to condensate
return system and open test tee. If trap:
Yarway Model 741
a. starts to cycle normally, it may be
assumed that elevated back pressure in
the condensate return system has caused
trap to fail open; seek and correct cause
of system problem.
b. fails to cycle and blows steam and
condensate continuously, it can be
concluded internal parts have failed;
repair or replace trap.
Cold disc trap
If it has been established that the system is
not the cause of the trap being cold:
1.Open strainer blow-down valve in front of
trap to purge it of dirt or air. If trap fails
to start normal function, then
2. Close block valves and disassemble trap
to clean passages. If inspection reveals
damaged intervals, repair or replace
the trap.
Yarway Model PB40
Checking thermodynamic traps (disc, piston and lever traps)
Piston and lever trap – mechanical failure mode
• Piston and lever traps fail in the open position. Seating surfaces wear and erode so that trap
can no longer close tightly.
Hot piston or lever trap
Cold piston or lever trap
Follow same procedure described for checking
disc traps. Note that these traps are designed
with a control flow orifice. This small orifice
will constantly discharge condensate between
normal full open cycles of the main valve. If
control flow discharge appears excessive,
inspect trap valve seat for wear.
Follow same procedure described for checking
disc traps. Note that these traps have good
air handling characteristics and are not
susceptible to air binding.
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Checking thermostatic traps (bellows, bimetallic, diaphragm and wax capsule)
Bellows trap – mechanical failure modes
• Many bellows traps fail closed due to a ruptured bellows that allows the valve to be pressed
closed against the seat. Some trap manufacturers provide a bellows that allows the valve to
move to an open position if the bellows ruptures.
• Bellows traps can also fail open due to wear and erosion of the valve and seat or extreme
bellows distortion that prevents valve from contacting seat.
Hot bellows trap
Confirm that seat and valve are momentarily
capable of being shut, and that bellows is 'alive'
by:
1.Partially opening strainer blow-down valve
in front of trap to drain condensate from line
and expose trap to dry steam.
2. Witness shut-off of trap discharge by
means of downstream test tee.
3. Failure to see tight shut-off confirms
trap needs repair or replacement.
Using a listening device or temperature
sensor can assist in confirming that bellows
is 'alive' and cycling if test tee is not available
to witness trap’s response to dry steam.
If cycling is not evident, it may be induced
momentarily by shutting off upstream block
valve for a minute or two to artificially backup
condensate. Releasing condensate will cause
trap to open briefly, before closing again, thus
demonstrating that bellows is 'alive'.
Listening devices can occasionally detect
steam leakage if seat and valve are sufficiently
worn to prevent tight shut-off. If tight shut-off is
still doubtful, close block valves, disassemble
trap and inspect bellows and seat for erosion.
Cold bellows trap
If it has been established that the system
is pressurized and is not the cause of trap
being cold:
1. Close block valves and disassemble trap to
inspect it for failed bellows or need to clean
flow passages of dirt.
2.Repair or replace trap if bellows is ruptured
or spongy.
Checking thermostatic traps (bellows, bimetallic, diaphragm and wax capsule)
Bimetallic trap – mechanical failure modes
• Most bimetal traps fail in the open position because bimetal elements tend to fatigue in a steam
environment and lose their ability to close valve tightly.
• Erosion of seat and valve results from trap’s failure to close tightly due either to dirt or
weakened bimetals.
Hot bimetal trap
Cold bimetal trap
Follow same procedure described for checking
performance of hot bellows trap.
If it has been established that system is
pressurized and is not the cause of trap
being cold:
1. Close block valves and disassemble trap
to inspect it for dirt or other obstruction.
Repair or replace trap if internals appear
damaged.
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Diaphragm capsule trap – mechanical failure modes
• Diaphragm capsule traps are relatively new, with less field experience than that associated with
bellows or bimetallic types. They are designed to fail in an open condition should diaphragm
crack and its liquid fill be lost.
Hot diaphragm trap
Cold diaphragm trap
Follow same procedure described for checking
performance of hot bellows traps.
Cycling of diaphragm trap is slower and less
distinctive than is typical of bellows trap.
Several minutes may be required for a closed
trap to open to discharge condensate.
If tight shut-off is impossible, trap should
be repaired or replaced.
If it has been established that system is
pressurized and is not the cause of trap
being cold:
1. Close block valves and disassemble trap
to clean dirt from flow passages (small
passages and condensate flows make this
trap more susceptible to dirt accumulation
than other trap types).
Constant temperature wax capsule trap – mechanical failure modes
The use of a temperature sensitive wax-filled capsule to open and close a trap is a relatively new
technique. These traps discharge condensate at a single predetermined temperature which may
be adjusted. They are designed to fail in the open position should the capsule lose its fill.
Hot constant temperature trap
Cold constant temperature trap
Follow the procedure described for checking
performance of bellows traps.
Objective is to establish that trap can shut-off
tightly. Once closed, it may require several
minutes to open. If trap is unable to shut-off
tightly, repair or replace it.
If it has been established that the system
is pressurized and is not the cause of trap
being cold:
1. Close block valves and disassemble trap
to inspect it for dirt or other obstruction.
Checking mechanical traps (bucket, float and thermostatic)
Bucket trap – mechanical failure modes
• Bucket traps tend to fail in the open position. The 'prime', necessary to float the bucket and
close the valve, can be evaporated so that the trap cannot shut off. The valve and seat also wear
and become eroded over time so that they can no longer shut off tightly. Bucket traps can also
fail in the closed position. If the bucket vent hole becomes clogged, air can keep the trap closed.
Higher than expected steam pressures also may prevent the bucket from opening the trap.
Hot bucket trap
Cold bucket trap
Using a listening device or by witnessing
discharge pattern, determine if trap is cycling,
thus confirming free movement of bucket.
1. If cycling is visible, verify valve and seat
condition by observing tight shut-off when
trap is in closed portion of its cycle.
2. If cycling is not visible, close upstream block
valve for several minutes. This will allow
condensate to accumulate in front of the
trap. Opening the block valve will enable
condensate to reprime trap or induce
temporary cycling if line conditions are
causing trap to operate in its less typical
modulating mode.
3.Trap should be repaired or replaced
if cycling cannot be induced or if tight
shut-off is not visible.
If it has been established that the system is
pressurized and is not the cause of the trap
being cold:
1. Verify that line pressure does not exceed
trap’s rated pressure. Such a condition will
cause trap to remain in the closed position.
If over-pressurization is not the problem, close
block valves and disassemble trap so that
internal parts can be inspected. Dirt and oxides
may need to be cleaned from bucket air vent
hole. When air cannot be removed, bucket will
float, holding valve closed.
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Yarway Industrial steam trapping handbook
Chapter 6 - Steam trap maintenance and troubleshooting
Checking mechanical traps (bucket, float and thermostatic)
Float and thermostatic trap – mechanical failure modes
• Float and thermostatic traps can fail in either a closed or an open position. They fail closed if the
float is ruptured by water hammer and can no longer rise to open the valve. They also fail closed
if the thermostatic element fails and air cannot be vented from trap.
They fail open when the main valve and seat or thermostatic air vent valve and seat are worn or
eroded so that they leak steam.
Hot float and thermostatic trap
Cold float and thermostatic trap
Because trap is designed to drain condensate
continuously, verification that valve and seat of
trap and air vent are not leaking steam is very
difficult unless leakage is very large.
1.Examine trap discharge pattern for evidence
of excessive vapor – i.e., steam leakage.
2. If possible, drain condensate through
strainer blowdown vent in front of trap to
determine if both trap and air vent valve
can close tightly in the presence of dry
steam. Tight shut-off establishes that
trap’s condition is good. Failure to shut-off
tightly indicates that trap needs repair or
replacement.
If it has been established that the system
is pressurized and is not the cause of trap
being cold:
1. Verify that system pressure does not exceed
rated pressure of trap. This can prevent
float from opening valve.
2. Close block valves and disassemble trap
to examine internal parts for damage
especially thermostatic air vent. Also
inspect for flow obstructions.
Summary
The subject of steam trap maintenance is best
summarized by three key points:
1. Careful selection and sizing of a suitable
steam trap type is important, but regular
maintenance is essential to the efficient
and reliable steam system.
2.Taking the time to establish steam trapping
standards for a plant repays its initial
costs year after year because it simplifies
steam trap checking and the maintenance
program.
3.Regardless of plant size, steam trap
maintenance should be recognized as a
specialized activity requiring specialized
knowledge and experience on the part of
those expected to do the job. The costs
of doing this job well are trivial when
compared to the costs of doing it poorly.
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Chapter 7 – Introduction
Today, an estimated 75% of installed steam
traps discharge into closed condensate
return systems, compared to less than 50%
a few years ago. Energy saving reasons for
this increased usage are covered in the brief
description of such systems in Chapter 5; the
discussion there also emphasizes that these
systems have the potential for creating trapping
problems.
In general, traps discharging into condensate
return lines have much higher failure rates
than those discharging to atmosphere. Design
of return piping can contribute to such failures
and hence warrants serious attention.
Designing return piping
Proper design of return lines is a complicated
task. Correct pipe length and diameter are
difficult to predict, so a method is given here
to provide a first estimate. (It also can be used
to estimate the impact of various line sizes on
system pressures).
The Yarway method of estimating return line
size differs from other published methods in
a number of ways. These differences and the
assumptions involved are as follows:
1.The condensate is assumed to be a
homogeneous mixture of liquid and
vapor as it is discharged from the steam
trap, and while it is traveling through the
return piping.
2.The mixture is assumed to be at constant
temperature; therefore, there is no
condensation of vapor or cooling of liquid.
This results in an estimate of larger
pipe size.
3.At the lower initial steam pressures,
velocities of the liquid/vapor mixture are
limited to lower values; in general, this
produces lower velocities with larger
proportions of liquid. Some methods
assume a constant return line velocity for
the mixture in the range of 3,000 fpm to
7,000 fpm. Such velocities are relatively
high and can produce erosion of the pipe,
especially where there’s a very small
percentage of flash and a large proportion
of liquid.
4.The velocity profile for a typical turbulent
situation is used. This further limits
velocities and pressure drops.
5.The installed steam trap capacity, not
condensate load, is considered an
important factor.
6.A guide for fractional loads from manifolded
traps is provided.
When condensate return line sizing is
inadequate, it is due to one or more of the
following reasons:
• The lines are receiving discharge from a
greater number of sources than originally
planned. This may be due to plant expansions
or energy conservation programs.
• Lines carrying steam at varying pressures
are discharging into a common return line.
• The steam traps are oversized and/or
misapplied.
• The return line design, initially, was
under-sized or marginal, or the piping
installation was inadequate.
Whatever the conditions leading to the
inadequacy of return lines, the results are
overpressurization of the return system,
venting of excessive amounts of vapor to the
atmosphere, vapor binding of condensate
pumps, noise, and unsatisfactory steam trap
operation. All of these shorten trap life, impede
drainage, promote freeze-ups, and increase
maintenance time as well as cost.
Guidelines for system components
Yarway has developed guidelines for the
design or use of the various components
of a condensate return system. They are
summarized in the following paragraphs and
more broadly applicable considerations are
given in the next section.
Steam main: the main, which carries steam
from the boiler to headers or other distribution
lines, should be of sufficient size to handle flow
in the existing plant plus any additional flows
required by plant extensions or additions. In
this way, the heat user will have steam at the
expected (design) pressure and temperature.
The main should be well drained of condensate
and vented free of air and noncondensibles.
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Steam header or distribution line: carrying
steam from the main to the heat user, this line
should be sized adequately for the flow rate
required so that it does not impose a severe
pressure drop. It may have a control valve and
should then be connected to the top of the
steam main; the installation should include
'drip' traps to protect the control valve and
assure moisture-free steam to the heat user.
The important point to remember for the steam
header or the main is to be sure they provide
steam at the conditions anticipated.
Heat user: tracing lines, unit heaters, heat
exchangers, and process equipment are typical
examples of heat users. Each should have
an adequate 'pocket' or hot well to collect
condensate. When provision is made for
condensate collection, consideration should
be given to guidelines for other process
equipment - such as those for pumps that drain
a vessel for entrance loss and separation of
steam bubbles from liquid condensate.
Fittings: to handle condensate that forms
at saturation temperature, fittings from the
heat user to the steam trap should be full
bore. Requirements are similar to those for
the prevention of 'pre-flash' at control valves.
Maximum possible pressure at the steam trap
inlet should be assured. Trap size should be
reduced only at the trap outlet.
Steam trap: traps should be selected for
specific applications. Design of the application
should be taken into account, as well as the
operating pressure and temperature ranges
especially if the heat user has a control valve on
the steam supply. Variations in condensate load
should also be considered.
The steam trap should not be selected on the
basis of pipe size and should not be oversized.
On process equipment, a trap may be judged
oversized if it has a safety load factor (SLF)
of 10:1 or more.
To provide gravity drainage to the trap, it should
be installed below the equipment. It should
also be installed for ease of checking and
maintenance.
Trap discharge line: oversized piping rarely
creates problems; the line should never be
undersized. It should be adequate to handle
flashing condensate. All traps discharging
near saturation temperature, or where
condensate temperature is above saturation
temperature for the return line pressure, will
form flash vapor. The trap manufacturer’s
recommendation should be followed and the
line sized for the instantaneous discharge
rate of the trap.
If used, check valves should be suitable for the
operating conditions; this requirement should
be verified with the check valve manufacturer.
If present, lift of the discharge line to the
return line should be accounted for (a lift of 2
feet adds approximately 1 psi to the pressure
at the steam trap outlet). The discharge line
should enter the return line on the top and not
be directly opposite any other discharge line
(see Figure 7.2 c and 7.2 d).
General design considerations
In the design of condensate return systems,
there are some general considerations which
can affect sizing of more than one component.
Also, some of these pertain to problems that
can come from undersized and overloaded
systems.
Steam traps: the instantaneous discharge rate
of the trap can contribute to overloading of the
return line. If the trap is of the 'fail open' type,
the amount of steam it can put into the line
must be allowed for.
Because traps differ in operating principles,
some may tend to get 'hot' when discharging
into high pressure. This can cause accelerated
wear of such traps as well as overloading or
over-pressuring of the return line. Risk of
steam loss also increases. Further, some types
of traps tend to back up condensate if return
pressures are elevated.
Figure 7.1
From steam
drip stations
Drip trap collecting
manifold - size based
on 25-50% of installed
trap flow rate
From tracer
collecting manifold
From tracers
Tracer collecting
header – size based
on sum of flows from
individual manifolds
Tracer trap collecting
manifold – size based
on 25-50% of installed
trap flow rate
From process
Ma
in r
etu
rn
Size based on 100%
of installed trap
flow rate
From processes
Process collecting manifold.
Size based on 75-100% of
installed trap flow rate
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Condensate load: when the steam trap is
sized, the smallest possible SLF should be
used. Variations in ambient conditions must be
checked out as to having a significant influence
on condensate load, steam pressures, or
condensate lines. Winter, for example, tends
to result in lower steam pressures and higher
return pressures. Sizing of the system may
also be significantly affected by startup loads.
Piping: because it is very likely that the piping
will have to serve some future plant expansion,
it is best to provide for such growth in the initial
design.
Allowances should be made for possible
damage to piping. One cause is high velocity
liquid that can result in erosion. Also, there
can be excessive noise and/or cavitation
damage. Corrosion is a frequent problem and is
specifically important if erosion is also present.
Deposition of 'dirt' reduces pipe bore and thus
is a problem.
Collection headers: a separate return line may
be advisable for each steam header pressure.
This prevents discharge of a high pressure
system from interfering with drainage and
proper operation of a lower pressure system.
Collection vessel (or receiver tank): a vessel
of sufficient size (volume) should be used, with
the quantity of flash vapor taken into account.
Its location should permit gravity flow from the
return line into it.
If pumps are used to drain the liquid from
the tank, there must be adequate NPSH
(net positive suction head) on the pumps for
the liquid temperature involved. Pumped
liquid should be figured to be at saturation
temperature for the pressure in the vessel.
Vents and reliefs should be added, as needed
and required by appropriate codes and
standards. Also, transient loads should be
allowed for; these include start ups, bypasses,
and failed traps that may blow into the system.
Overloaded receivers result in venting of
excessive flash vapor and loss of energy. If the
return is to a condenser, excessive cooling
water is used.
If the collecting vessel is over-pressurized,
liquid temperature can be too high for the
selected condensate pump. This can result in
vapor binding of the pump and damage to the
pump itself.
Insulation: insulation of the return system
helps conserve energy, but it maintains high
flashing fluid temperatures that can make fluid
handling difficult. Fluid handling problems,
however, are overcome by proper regard for the
nature of hot condensate and proper selection
of components.
Safety: settings and size of relief valves and
vents should be reviewed, especially if these
must relieve a flashing liquid. As mentioned
previously, transient situations – such as start
up loads, open bypasses and blowing traps –
should be allowed for.
Return line installation
1. For gravity flow, the line should slope
toward the receiver (see Figure 7.7 a).
Preferably, the slope should be constant;
risers and pockets that produce shock and
water hammer should be avoided.
2. With eccentric reducers, to accommodate
larger pipe for larger loads, expansion
should be on the bottom of the pipe
(see Figure 7.7 b).
3.Discharge lines should be into the top of
return lines so that they discharge into
the vapor space and thus reduce noise
(see Figure 7.7 c).
4.Discharge lines should be staggered to
minimize noise, high local back pressure,
and potentials for erosion (see Figure 7.7 d).
5. If heat using equipment must be gravity
drained, the trap discharge line and the
return line must be below the drainage point
of the heat user. The return line should be at
least two or three feet below the heat user
outlet. Care should be taken with regard to
possible freezing situations.
6.Alignment and support should be adequate
for the main return line. Anchors are
normally required. The code for power
piping, ANSI B31.1, should be referred to.
Consideration must be given to the weight
of pipe itself, fittings, flanges, valves,
insulation, and the fluid itself. The fluid
should be assumed as being all liquid
because hydrostatic testing is probably
needed.
Figure 7.2
a. Slope toward receiver
Flow
Slope
b. Expand on bottom
Slope
Flow
Eccentric
reducers
c. Discharge in top
Trap discharge line
Return line
flow
d. Discharge not opposite
Flow
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Other potential factors – such as wind, snow,
ice, shock, seismic effects, vibration, and
thermal stresses – need to be included in
the considerations.
Estimating return line size and maximum load
Figure 7.3 is a nomograph that can be used
for estimating the return line I.D. and also
maximum load (condensate rate) that a given
return line can handle. There are three basic
elements involved in such estimates; these
are defined by the equation:
W = (Factor X) (Factor Y)
When:
W = maximum discharge rate (catalog ratings
in lb/hr) of all steam traps discharging into
the return line, multiplied by a percentage
that depends upon the trap application
(25 to 50% for drips and tracings and
75 to 100% for process)
Alternately, for a given return line,
W = maximum carrying capacity in lb/hr of
flashing condensate for all steam traps
in the system
X = flash factor for various steam trap inlet
pressures, P1, and flash tank pressures,
P2, in psig (see Figure 7.3)
Y = pipe factor for various return line I.D.’s
in inches and equivalent pipe lengths, Le,
in feet (see Figure 7.3)
Included in factor X are considerations for
a limiting pressure drop, percent of vapor
formed, and the average density of the
two-phase mixture (the latter is assumed
homogeneous). Included in factor Y is a pipe
friction factor for complete turbulent flow; this
factor is based upon Figure 20 in the hydraulic
institute pipe friction manual for steel pipe.
Sizing flash and receiver tanks
There are certain characteristics of a
condensate return system that can affect how
flash and receiver tanks are applied. These will
be considered before the matter of tank sizing
is covered.
Condensate and flash vapor should be piped
into the top of the receiver. If the liquid
condensate is returned, but no attempt is made
to use the flash vapor, the receiver can be
vented from the top to atmosphere.
An unvented receiver is satisfactory as long
as the heat in the flash vapor can be absorbed
in the receiver while the condensate is being
pumped back to the boiler feed tank. If the flash
enters the closed receiver faster than it can be
absorbed, however, pressure in the receiver
and return lines can interfere with performance
of the system steam traps. Appropriate safety
and relief valves are necessary.
In a flash condensate recovery system, a
helpful and sometimes indispensable adjunct
to the receiver is a flash tank that operates
at some pressure above atmospheric. The
flash condensate and its liquid are directed
into the flash tank either through a top inlet or
centrifugally through a side inlet near the top.
Figure 7.5 illustrates these connections as well
as steam and water outlets.
Figure 7.5
Condensate and flash steam recovery system
High pressure
condensate from traps
Low pressure flash steam
Drip traps
H-P flash
tank
Atmospheric vent
Low pressure
condensate
from traps
Condensate
pump
Carefully size and
select condensate
pumps and controls
Atmospheric
receiver
To boiler-feed system
Condensate pump
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Table 1
Maximum ratings, centrifugal and top-inlet tanks, 1,000 lb/hr of flash steam
Flash tank pressure psig
Tank no.
1
Centrifugal flash tanks
2
1.5
3
3.2
4
6.0
5
16.0
6
27.0
Top-inlet flash tanks
2
3
4
1.1
2.2
4.3
2
5
10
20
30
40
1.6
3.4
6.1
17.0
29.0
1.8
3.9
7.1
20.0
34.0
2.3
4.9
8.8
24.0
42.0
3.0
6.4
12.0
32.0
58.0
3.9
8.5
15.0
41.0
73.0
4.8
10.0
18.0
49.0
89.0
5.5
7.5
9.5 13.0 17.0
12.0 16.3 20.0 27.7 35.0
21.0 27.0 34.0 50.0 66.0
58.0 79.0 100.0 142.0 184.0
105.0 142.0 180.0 254.0 329.0
1.1
2.5
4.6
1.3
2.9
5.2
1.7
3.5
6.5
2.2
4.9
8.7
2.8
6.1
10.8
3.4
7.4
12.0
4.0
8.7
15.0
Dimensions of commercial flash tanks
75
5.5
11.8
20.0
100
6.9
14.8
25.0
150
10.0
21.4
36.0
200
13.0
25.4
46.0
Tank
height, in
Overall
height, in
Inlet-pipe
size, in
Centrifugal flash tanks
2
24
3
36
4
48
5
60
6
72
56
62
67
78
89
65
72
77
88
99
2
3
4
6
8
3
4
6
8
10
1½
2
4
5
6
Top-inlet flash tanks
2
24
3
36
4
48
56
62
67
65½
71½
76½
3
4
6
3
4
6
1½
2
4
Tank no.
Outside
dia., in
50
Outlet-pipe
Steam
Water
Rule-of-thumb sizing method: one method by which a flash tank can be sized is based on the
assumption that the lb/hr of steam that can be flashed per square foot of water surface is three
times the absolute pressure inside the tank would be:
Ws/A = 3 (P2)
Where:
A = water surface in square feet
P2 = flash tank pressure in psia
Ws = lb/hr of flash vapor (steam)
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Table 2
Percent of flash steam formed
Initial steam
Sat.
pressure
temperature
psig
°F
25
267
50
298
75
320
100
338
125
353
150
366
175
377
200
388
225
397
250
406
300
422
350
436
400
448
450
459
500
470
550
480
600
489
Total heat of flash steam, BTU/lb
Flash-tank pressure, psig
0
5.7
9.0
11.3
13.3
14.8
16.8
17.4
18.7
19.7
20.7
22.4
24.0
25.5
26.8
28.2
29.2
30.2
5
4.1
7.4
10.8
11.7
13.4
14.8
16.0
17.5
18.2
19.2
21.0
22.7
24.2
25.3
26.7
27.8
28.8
10
3.0
6.2
8.6
10.6
12.2
13.7
15.0
16.2
17.0
18.2
20.0
21.6
23.0
24.4
25.7
27.0
28.0
20
1.0
4.3
6.7
8.7
10.3
11.8
13.0
14.4
15.4
16.4
18.2
20.0
21.5
22.7
24.0
25.3
26.4
30
2.6
5.0
7.0
8.7
10.2
11.6
12.8
13.8
15.0
16.7
18.4
20.0
21.2
22.6
23.7
25.0
40
1.0
3.7
5.7
7.4
8.8
10.0
11.5
12.4
13.6
15.5
17.0
18.7
20.0
21.4
22.6
23.6
50
2.5
4.6
6.3
7.8
9.0
10.4
11.4
12.5
14.4
16.0
17.7
19.0
20.4
21.6
22.7
75
2.2
3.8
5.4
6.7
8.0
9.0
10.0
11.0
13.8
15.6
16.8
18.2
19.5
20.5
100
1.7
2.3
4.6
6.0
7.0
8.2
10.0
12.0
13.5
15.0
16.4
17.5
18.7
125
1.6
3.0
4.4
5.4
6.6
8.5
10.4
12.0
13.4
14.6
16.0
17.3
150
1.5
2.8
3.8
5.0
7.0
8.9
10.5
12.0
13.4
14.7
16.0
1150.0
1156.0
1160.0
1167.0
1172.0
1176.0
1179.0
1185.0
1189.0
1193.0
1195.0
970.0
960.0
952.0
939.0
929.0
919.0
912.0
895.0
881.0
868.0
857.0
180.0
196.0
208.0
227.0
243.0
257.0
267.0
290.0
309.0
324.0
338.0
212.0
228.0
240.0
259.0
274.0
287.0
296.0
320.0
338.0
353.0
366.0
26.8
20.0
16.3
11.9
9.4
7.8
6.6
4.9
3.9
3.2
2.7
Latent heat of evaporation, BTU/lb
Heat of liquid, BTU/lb
Saturated water temperature, °F
Volume of flash steam, ft·lb
For horizontal tanks, this rule works satisfactorily and is often used. It usually oversizes the tank
because it does not take into account the large steaming surface area of the condensate as it
flows through the return lines to the flash tank.
Example:
Assume the inlet pressure to the traps is 100 psig and the receiver pressure is 30 psig.
Also assume a total discharge of 10,000 lb/hr.
Solution:
1. From Table 2 determine that the flash is 7%.
2.Multiply total load by 7% 10,000 lb/hr x .07 = 700 lb/hr flash
3. Convert receiver pressure 30 psig to absolute pressure 30 + 15 = 45 psia
4.Solve the equation
Ws/A = (P2)
700/A = 3 (45)
A
= 5.185 ft2
A horizontal tank with 1½ foot I.D. and 3½ foot internal length would provide sufficient area
(Ph x 3½ = 5.25 ft2)
L = 3½’
D = 1½’
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Experience method: because it is difficult
to arrive at an accurate figure for the total
steaming surface in a condensate system, flash
tank sizing is frequently based on experience.
This method will be discussed with reference to
Table 1. The first table develops the dimensions
as well as the design of the tank; Figure 7.6
illustrates the height dimensions and identifies
the several inlets and outlets.
Table 2 tabulates percentages of flash
vapor formed at various values of flash-tank
pressures and initial steam pressures. Its use
is discussed later.
Table 1 gives separate ratings for (a) centrifugal
flash tanks and (b) top-inlet tanks. Size for size,
ratings for top inlet tanks are approximately
70% of those for centrifugal inlet tanks. In the
centrifugal type, the condensate spirals around
the inside of the tank as it falls to the bottom;
the longer path provides more time and
surface for steam flashing.
Separation of vapor from liquid in the tank
is important. This is frequently improved by
insertion of a screen or 'demister'.
When the type and size of the flash tank
are being chosen, it should be born in mind
that, if operating pressure is increased, the
permissible velocity of flash steam entering
the tank should be lowered. This prevents
condensate from being carried over into the
low pressure steam line.
Ratings in Table 1 have been worked out
to avoid the carrying over of condensate. In
addition, the steam outlet line should be amply
sized because its diameter bears directly on the
exit velocity and, of course, on the possibility of
condensate being carried over.
Sizing a vented receiver: Table 2 can also be
used when the size of a vented condenser is
being selected (a flash tank not being included).
This table gives the amount of flash vapor
formed for various combinations of trap inlet
and tank pressures.
If Table 2 is used in the selection of a vented
receiver, the tank pressure should be assumed
to be less than 5 psig, because the flash
condensate will flow freely to the atmosphere.
The amount of flash will actually be less than
that for the maximum tank rating if the receiver
is sized similarly to the tank.
In an existing installation, if the condensate
pressure (and temperature) in the receiver is
high enough to cause flashing and cavitation
in the receiver pump, the difficulty can be
alleviated temporarily by an increase in
the size of the steam outlet or the vent. An
alternate solution is to install a flash tank
ahead of the receiver.
Example of calculating tank size
(including flash vapor and its heat content)
As an example, in an industrial plant, there
are 50 steam traps of several different
sizes, discharging a total of 95,000 lb/hr of
condensate from equipment operating at
150 psig. The condensate flows to a vented
receiver that operates at 5 psig.
The first questions to be considered are:
“How much flash vapor is formed if the
condensate is discharged very near to steam
temperature?” And “How much heat is
available in the flash steam?”
To determine the amount of flash vapor formed,
150 psig is located in the left-hand column of
Table 2 and lined up with the vertical column
for a flash-tank pressure of 5 psig. This gives
a figure of 14.8% for the amount of condensate
that forms flash vapor. The quantity of flash
vapor is thus 95,000 x 0.148 or 14,060 lb/hr.
To determine how much heat is available
in this vapor, the latent heat of evaporation
at 5 psig (at the vented receiver) is figured
at 960 BTU/lb. The flash vapor thus
provides nearly 13,500 million BTU/hr
(14,060 x 960 = 13,497,600).
If this heat energy were used to heat water
from 40°F to 140°F (a 100°F rise) and the
water heater had an overall efficiency of
85%, 114,730 lb/hr of water would be heated
(13,500,000 x 0.85 x 1/100 = 114,730). That is
nearly 230 gpm. In addition, the condensate
from the water heater could still be returned
to an atmospheric pressure receiver and used
again in the boiler.
Now the question can be considered: What
size and type of flash tank would be selected
and what would be its dimensions?
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Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
From the above calculations, it is assumed that
the 14,060 lb/hr of flash steam is available at
5 psig for heating equipment. In Table 1 the
5 psig value for flash tank pressure is located
in the horizontal line of figures across the
table. The vertical column under this figure
gives the maximum ratings of flash tanks for
this pressure (note that these are given in
thousands of lb/hr so that 1.8, for example,
means 1,800).
For the available 14,060 lb/hr of steam
flow, a no. 5 tank with a maximum rating of
20,000 lb/hr (20.0 in the table) would be the
proper size. The tank would have to be a
centrifugal-inlet type because no standard
top-inlet type shown in the table has sufficient
capacity.
The lower part of the table gives the dimensions
of the tank. The no. 5 centrifugal tank has
a 60” diameter, an overall height of 88” and
a 78”. tank height. It has a 6” condensate inlet,
an 8” steam outlet, and a 5” liquid outlet at the
bottom. (These dimensions and connections
are identified in Figure 7.6).
Flash tank sizing – alternate method
Another means of estimating the size of a flash
tank and its associated piping is shown in the
nomograph of Figure 7.7. The graph is entered
from the left at given values of flow in lb/hr. As
explained in the example below, the percent
flash vapor table (Table 2) is used to determine
the quantities of flash vapor, liquid, or total of
the two, in lb/hr. All three of these flows are
used in the estimation of dimensions.
The graph is entered at the proper flow value
and pertinent tank dimensions are obtained
at intersections with curves A through E.
As illustrated in Figure 7.7, the dimensions, in
inches, are:
A = t ank height, based on total liquid and
flash flow
B = t ank I.D., based on total liquid and
flash flow
C = c ondensate inlet I.D. based on total
liquid and flash flow
D = f lash outlet I.D., based only on flash
portion of arriving condensate. To assure
adequate size, no allowance is made for
condensation of flash.
E = liquid outlet I.D., based on liquid portion of
arriving condensate; no allowance is made
for vapor condensation
Example: condensate to be collected is
30,000 lb/hr. Nominal steam pressure is
150 psig Atmospheric pressure is to be
maintained in tank.
Solution:
1. With reference to the table for percent flash
vapor (Table 2), 150 psig to atmosphere
gives 16.8% flash formed.
2. 30,000 lb/hr x 0.168 = 5,040 lb/hot flash
vapor.
3. 30,000 – 5,040 = 24,960 lb/hr of liquid.
4.On Figure 7.7, at 30,000 lb/hr, for total liquid
and flash flow, dimensions for A, B, and C
are determined as 47 in, 21 in and 7 + in,
respectively.
5.On Figure 7.7, at 5,040 lb/hot flash only,
dimension D for the flash outlet I.D. is
determined as 7 in.
6.On Figure 7.7, at 24,960 lb/hr of liquid only,
dimension E for the bottom liquid outlet J.D.
is determined as 2 in.
7.As a last step, applicable codes, standards,
and the like should be consulted for final
design of the tank, walls, supports, vents,
reliefs, etc.
Figure 7.6
Sizing top or centrifugal inlet tank
Top inlet
Centrifugal inlet
Blowdown inlet
Tank height
Overall height
Steam outlet
Water outlet
62
Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Design factors that save money
In the disposition of flash condensate, money
can be saved and operating headaches avoided,
if the following suggestions are heeded during
the design of the condensate return system:
1.The return line should be sized to carry the
flash vapor as well as the liquid condensate.
Undersized lines cause high back pressures
at the traps; this reduces their effectiveness.
2.All steam equipment in the process
should be analyzed to determine: (a)
which units provide a continuous supply
of high temperature and high-pressure
condensate that can be used, and (b) what
equipment can operate on low-pressure
flash condensate. Some equipment may
be operating on boiler steam that is being
reduced. Present operating pressures and
temperatures of this equipment should
be checked; they may be higher than
necessary.
3. For each case, the economies of using flash
condensate should be checked out. This
kind of saving, which goes on from year to
year, should be balanced against the cost
of installing the flash-condensate recovery
system.
4.The pipeline that carries the flash vapor
should be sized to lessen pressure
drop between the flash tank and the
low-pressure steam equipment. Also,
money can be saved if the flash tank and
pipeline are insulated. Further, condensate
return lines should be insulated so that
the maximum amount of flash steam is
recovered. If the flash L-P heating pipeline
is long, drip traps should be installed.
5.The flash tank (and the receiver tank, if
it is not vented) should be constructed in
accordance with the ASME unfired pressure
vessel code. Local codes, insurance
company requirements, and plant standards
should be checked. The role of applicable
codes and standards cannot be minimized.
ANSI B31.1 code for power piping contains
specific requirements; for example,
Para. 102.2.5(c).
6.Types of traps already in use should be
checked. Some types discharge condensate
near steam temperature; others require
that the condensate cool considerably
before they open and discharge. The former
types produce more flash condensate and
return the most heat. Some types of traps
discharge subcooled condensate and the
latent heat is lost to ambient if the system
does not accommodate backup.
7.A systematic plan for using flash
condensate can save heat, cut fuel costs,
and improve process efficiency. For the
best results, however, the whole system
and each of its parts should be carefully
analyzed.
8.The condensate pump must handle very hot
liquid. The pump, controls, and associated
piping should be carefully selected to
assure proper operation. Under adverse
conditions, the pump could 'vapor bind' or
cavitate. When this occurs, the liquid will not
be removed from the flash tank or receiver.
These vessels will then accumulate liquid
and possibly over-pressurize.
In addition to reducing the effectiveness of
the return system, over-pressurization can
result in a safety hazard.
9.A frequent solution to over-pressurized
tanks and systems is to drain them to
sewer or grade. For vessels under these
conditions, relief or safety valves should be
considered. Again, applicable codes and
standards for valve sizing, selection, and
installation should be consulted.
All design consideration of the condensate
system must include a full review of ASME
code and section 8 piping code. Applicable
codes and engineering calculations are
required for any condensate systems. This
guide is not intended to discuss any specific
ASME code requirements and each users
must satisfy all code requirements prior
to installation of any condensate system.
63
Yarway Industrial steam trapping handbook
Chapter 7 - Condensate return systems
Figure 7.7
8
6
5
4
3
2
'E'
bas
ed
on
liqu
id o
nly
100,000
8
6
5
4
Step 4
3
Step 6
'C'
bas
ed
on
tot
al l
iqu
id a
nd
fla
sh
flo
w
2
10,000
8
Step 5
6
5
4
1,000
8
6
5
4
3
'A' b
ased
on
'D'
'B'
bas
bas
ed
ed
on
on
fla
tot
sh
al l
onl
iqu
y
id a
nd
flas
h fl
ow
Flow, lb/hr
2
tota
l liqu
id an
d fla
sh fl
ow
3
2
100
1
2
'E'
3
4
5
6 7 8 9 10
'D' 'C'
20
'B'
30
40
50 60
100
'A'
Dimension, NPS
64
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Appendix A
Listed below, alphabetically, are over 90 typical pieces of process equipment. They are identified
by type and class (number and letter). To obtain a trap type recommendation, with appropriate
installation tips, match the type and class designation to comparable reference on one of the
following pages.
Equipment Type Class
Equipment Type Class
Acid vat................................................ 1A,C
Air blast coil........................................ 2B
Air dryer............................................... 2B
Air heater............................................. 2B
Air preheater....................................... 2B
Asphalt tank........................................ 1A
Autoclave............................................. 4A
Batch dryer.......................................... 2B
Bayonet heater.................................... 1A
Belt press............................................ 3A
Bleach tank......................................... 1A,C
Blender................................................ 1A
Brew kettle.......................................... 1B
Cabinet dryer....................................... 2A,B
Calender.............................................. 3A
Candy kettle........................................ 1B
Chamber dryer.................................... 2B
Chamber, reaction.............................. 4A
Cheese kettle...................................... 1B
Confectioners’ kettle.......................... 1B
Continuous dryer................................ 2A,B
Conveyor dryer.................................... 2A,B
Cooking coil......................................... 1A
Cooking kettle..................................... 1B
Cooking kettle, tilting.......................... 1
C
Cooking tank....................................... 1B
Cooking vat.......................................... 1B
Cylinder dryer...................................... 3B
Cylinder, jacketed............................... 3B
Double drum dryer............................. 3B
Drum dryer.......................................... 3B
Drum, dyeing....................................... 1A,C
Dry can................................................. 3B
Dry kiln................................................ 2A,B
Drying roll............................................ 3B
Drying room........................................ 2A,B
Drying table......................................... 3A
Dye vat................................................. 1A,C
Dyeing bath.......................................... 1A,C
Dyeing drum........................................ 1A,C
Dyer, package...................................... 1A,C
Evaporator........................................... 1B
Feed water heater............................... 1A
Festoon dryer...................................... 2B
Fin type heater.................................... 2A
Fourdrinier.......................................... 3A
Fuel oil preheater............................... 1A
Greenhouse coil.................................. 2A
Heat exchanger................................... 1A
Heating coil-air blast fin type............. 2B
Heating kettle...................................... 1B
Hot break tank.................................... 1A,C
Hot plate.............................................. 3A
Kiers..................................................... 1A
Liquid heater....................................... 1A
Milk dryer............................................ 3A
Mixer.................................................... 1A
Molding press platen.......................... 3A
Package dryer..................................... 1A
Paper dryer......................................... 3B
Percolator............................................ 1B
Phono-record platen.......................... 3A
Pipe coil, circulating air...................... 2B
Pipe coil, still air................................. 2A
Platens, press..................................... 3 A
Plywood platen.................................... 3 A
Preheater, fuel oil............................... 1A
Preheating tank.................................. 1A
Plating tank......................................... 1A,C
Pressure cooker................................. 4A,B
Process kettle..................................... 1B
Pulp dryer............................................ 3B
Reaction chamber............................... 4A
Reheater.............................................. 1A
Retort................................................... 4B
Rotary dryer......................................... 3B
Shell and tube heat exchanger.......... 1A
Sterilizer.............................................. 4A
Storage tank coil................................. 1A
Storage water heater.......................... 1A
Stretch dryer....................................... 3A
Submerged coil................................... 1A
Suction heater..................................... 1A
Sugar dryer.......................................... 2B
Tank coil.............................................. 1A
Tank car coil........................................ 1A
Tire mold press................................... 3A
Tray dryer............................................ 2A,B
Tunnel dryer........................................ 2A,B
Unit heater........................................... 2B
Vat........................................................ 1A,C
Veneer platen/press........................... 3B
Vulcanizer............................................ 3A
Water still............................................ 1A
Water heater, storage......................... 1A
Water heater, instant.......................... 1B
65
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 1, Class A
Steam
Storage tank
Tank car
Steam
Steam heats a liquid indirectly through
a metal wall
Typical equipment:
• Asphalt tank
• Reheaters
• Suction heaters
• Bayonet heaters
• Storage tank
• Tank car
Activity: coils used to heat liquids (often very
viscous) in large weather exposed equipment
frequently in remote locations. Several coils
may be employed due to the large surface
area of containers.
Steam pressures: will range from 5 to 125 psi
with 40-75 psi being most typical. Generally
constant pressure but occasionally will be
modulated by pressure control valve.
Condensate loads: wide ranges in final
temperature of material being heated and in
ambient temperatures results in especially
large range of loads. Startup loads are typically
very heavy with seasonal weather variation
having a significant influence.
Drainage to trap: gravity drainage is the
normal condition.
Discharge from trap: generally to open drain.
Condensate return systems are often missing
due to distance from power house and low
pressures.
Ambient conditions: vary as widely as weather
conditions themselves – arctic to equatorial
desert.
Air venting: prompt venting of air is desirable
when frequent startups and rapid heating
requirements are the norm.
Shock, vibration and water hammer: may be
present during startup.
Dirt and corrosion: corrosion of coils can lead
to contamination of steam system by material
being heated.
Recommended traps
Desired characteristics: rugged, fail open,
self-draining with good air handling
Installation tips:
Strainer with suitable blow-down valve
should be placed ahead of trap. A suitable
drop or collecting leg (2’-3’) is desirable for
bimetallic trap.
66
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 1, Class B
Steam
Cooking oil
Hot process
fluid
Steam
Cool process
fluid
Full size pipe
Shell and tube heater
Steam heats a liquid indirectly through
a metal wall
Typical equipment: • Acid or bleach tanks
• Feedwater heaters
• Plating tanks
• Brew kettles
• Fuel oil preheaters
• Storage water heaters
• Dye vats
• Kettle coils
• Water heater, instant
• Evaporators
• Mixer or blenders
Activity: coils or jackets are used in tanks or
vats for heating liquids in either batch or the
continuous flow typical of shell and tube type
heaters. Equipment is generally protected from
the weather and of a size that one heating coil
is most typical.
Steam pressures: will range from 15 to 150 psi
with 40-75 psi most frequent. Some equipment
may see pressure up to 600 psi. Pressures may
be constant, but often modulated by pressure
control valve.
Condensate loads: heavy startup loads,
followed by smaller and steadier running loads
are to be expected, but without the extreme
swings of weather-exposed equipment.
Drainage to trap: gravity drainage is the
normal condition.
Discharge from trap: generally to closed
return with nominal pressures. Also overhead
lift to elevated condensate header or return.
Ambient conditions: protection from weather
may be partial or complete and equipment
tends to experience smaller temperature
swings.
Air venting: proper venting is important.
Equipment is often run on regular daily
or weekly schedules. Tendency is for total
shutdown of equipment following completion
of run or batch. Lack of adequate venting can
cause condensate to be drawn back into heat
exchange coils.
Shock, vibration and water hammer:
improperly drained coils lead to shock and
vibration during startup.
Dirt and corrosion: problems are aggravated
by poor drainage and frequent shut downs.
Recommended traps
Desired characteristics: rugged, fail open,
good air handling, rapid response rate, and
discharge condensate at close to steam
temperatures.
Installation tips: strainer with suitable
blowdown valve should be placed ahead
of trap. A vertical drop leg ahead of trap is
also recommended.
67
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 1, Class C
Steam
Submerged
coil
A Air vent
Jacketed kettle
Lift fitting
(see Figure 5.2)
Steam heats a liquid indirectly through
a metal wall
Typical equipment:
Air vent
Steam
• Cooking kettle, tilting
• Candy kettle
• Embossed coils
• Tanks with elevated
discharge
Activity: liquids or materials are heated
or cooked in jacketed kettles or tanks with
submerged coils. All require raising discharge
to the trap.
Steam pressures: generally 5 to 125 psi with
most frequently experienced pressures in the
middle of this range.
Condensate loads: startup loads heaviest with
running loads lighter.
Drainage to trap: condensate is passed to trap
through use of a lift fitting that creates a water
seal or reaches trap through syphon tube in
case of tilting kettle.
Syphon on
tilting kettle
Ambient conditions: equipment is generally
protected from the weather and unlikely to see
extreme temperatures (either) hot or cold.
Air venting: frequent startup and the need to
get equipment hot quickly requires a good air
venting.
Shock, vibration and water hammer: may be
present during startup.
Dirt and corrosion: poor drainage and frequent
startups increases potential for corrosion.
Recommended traps
Desired characteristics: resistant to steam
binding, rapid response, discharge condensate
at close to steam temperatures, rugged, fail
open, resistant to water hammer and shock.
Installation tips: auxiliary air vents are helpful.
Lift leg or syphon should be a smaller pipe size
than trap to reduce tendency for steam binding.
Discharge from trap: may be either to an open
drain or a closed pressurized return.
68
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 2, Class A
A
Auxiliary
air vent
Steam
Slope
Slope pipe
coils
Steam heats air/gas indirectly through a
metal wall
Typical equipment: • Dry kiln (without fans)
• Drying room
• Greenhouse coil
Activity: space heating or drying of materials in
enclosed equipment with natural air circulation.
Fans or blowers are not employed.
Steam pressures: typically 5 to 50 psi with
fluctuation occurring during startups. Normally
constant pressure without control valves.
Condensate loads: will vary widely depending
on the size of the exposed surface area of the
coils. Loads will be heaviest at startup and
rather steady thereafter.
Drainage to trap: gravity drainage is important
with amply sized collecting leg required to
prevent condensate backup into coils.
Discharge from trap: gravity to closed return,
low pressure to vacuum.
Ambient conditions: generally protected from
weather because installation is inside building
or structure. Seasonal changes can expose
shut-down system to freezing conditions.
Air venting: important to assure fast startups.
Shock, vibration and water hammer: on
startup hot condensate, flowing into improperly
drained coils or return system, can create
shock and vibration.
Dirt and corrosion: may be heavy due to
seasonal use, long shut-downs possibly in
flooded conditions.
Recommended traps
Desired characteristics: rugged, good air
handling, medium response rate, corrosion
resistant.
Installation tips: provide collecting leg and
strainer with suitable blowdown valve ahead
of trap.
69
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 2, Class B
Steam
Steam in
Vacuum
breaker
VB
Air heating coil
Unit
heater
Air
A
Air vent
Min. as recommended
by coil mfgr. up to
3 ft for modulating
steam and freezing
air temperature
Condensate return
Steam heats air/gas indirectly through a
metal wall
Typical equipment: • Chamber dryer
• Pipe coils (circulating air)
• Conveyor dryer
• Air preheater
• Dry kiln (with fan)
• Unit heater
• Fin coil
Activity: forced circulation of air over or
through coils for space heating. Also the drying
or heating of materials in either open or closed
containers or chambers with air circulation
created by fans or blowers.
Steam pressures: generally 25 to 150 psi with
50-75 psi most common. Pressures can vary
greatly due to cyclic off-on action, the changing
of dampers and mix of makeup air. Sudden
drafts of freezing outside air can lower coil
steam pressure to below atmospheric.
Condensate loads: vary greatly due to variety of
controls and changing inlet air temperatures.
Coils in series will have highest loads on first
coil with decreasing loads on successive coils.
High loads and low pressures will occur when
fan starts and cold air is blown over coils.
Drainage to trap: must be by gravity with a
sufficiently large collecting leg to momentarily
store condensate until trap can open and
discharge.
Discharge from trap: generally, discharge is
to a closed return system.
Ambient conditions: freezing is a major
concern when cold outside air can be drawn
into system. Dry kilns and heaters in hot areas
may expose traps to such high temperature
that some traps are adversely affected.
Air venting: very important to assure rapid
startup. vacuum breakers are recommended
to facilitate coil drainage on shut-down.
Shock, vibration and water hammer: often
from return lines on startup or improperly
trapped steam supply. Can also occur due to
inadequate drainage from coils resulting from
changes in load, pressures or the sagging
of coils.
Dirt and corrosion: corrosion can be a
significant problem if coils are manufactured
of dissimilar materials.
Recommended traps
Desired characteristics: rugged, fast
responding, hot discharge, fail open,
self-draining good air handling when subject
to frequent startups.
Installation tips: trap should be well below
unit (2 ft to 3 ft) with amply sized collection
leg. Air vents on larger equipment to aid
in startup. Vacuum breakers help assure
complete drainage of coils on shut-down. This
is especially important if freezing temperatures
are possible. Strainers with blow-down valves
and test 'T' reduce maintenance and simplify
trap troubleshooting.
70
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 3, Class A
Always below trap outlet
Platen
Steam in
Flexible
metallic hose
Typical - each
trap station A Air vent
Collecting
manifold
Platen press
Steam heats a solid or slurry indirectly through
a metal wall
Typical equipment: • Belt press
• Molding press
• Tire mold press
• Drying table
• Plywood press
• Vulcanizing equipment
Activity: molding, bonding, curing, drying
and vulcanizing materials such as plastics,
rubber, particle board, and similar substances.
Generally a 'finished' form is being developed
using platens or steam heated molds.
Steam pressures: generally in the range of
50 to 150 psi. Batch operation associated with
platens and vulcanizing presses can produce
wide changes in pressures.
Condensate loads: are quite variable. Platens
and presses have cyclic loads that are very high
during warming and then much lower when
maintaining temperatures. Some platens have
cold water introduced to arrest or control the
time temperature cycle.
Drainage to trap: typically drainage to the trap
is by gravity.
Discharge from trap: most frequently to a
closed return system.
Air venting: an important consideration for
this class of equipment due to the frequency
of startups.
Shock, vibration and water hammer: usually
comes from return systems or improperly
trapped steam supply. Rapid formation of
condensate slugs produce shocks as will
cold water injection into molds.
Dirt and corrosion: are significant factors,
especially in platens with air venting. Frequent
shut-downs encourages corrosion.
Recommended traps
Desired characteristics: rugged, having hot
discharge and fast response. Good air handling
due to frequent startup of equipment. Failure
mode should be 'open'.
Installation tips: mount trap below platen’s
lowest (open or closed) position. Flexible hoses
should be carefully selected for materials
and proper bore diameter to assure easy
drainage. They should be connected to provide
positive head to the trap when it is stationary
and downstream of hose. It is preferred that
the trap be mounted on and below the platen
outlet. A suitable flexible hose should be
connected to the trap outlet and the drain
header. The connection at the drain header
should always be below the trap outlet,
whether the platen is open or closed.
Ambient conditions: processing is generally
indoors. Temperatures are frequently hot due
to heat from equipment.
71
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 3, Class B
Steam
Syphon drained apparatus
Steam
(Trap arrangements typical
for cylinder ironer)
Cylinder dryer
Steam heats a solid or slurry indirectly through
a metal wall
Discharge from trap: discharge is generally
to a closed condensate return system.
Typical equipment:
Ambient conditions: generally hot due to heat
from the equipment.
• Calender
• Paper dryer
• Drum dryer
• Dry can
• Pulp dryer
• Fourdrinier
• Rotary dryer
Activity: continuous drying of materials is being
performed by exposure to the heated surfaces
of rotating cylinders or drums. Commonly used
in the manufacture of felt, asbestos, rubber,
textiles, paper and other sheet or fibrous
materials, including foods and slurries of
chemicals.
Steam pressures: generally in the range
of 75-150 psi. Once warm up is complete,
pressures are reasonably constant.
Condensate loads: high startup loads and
moderate running loads are typical. When
many dryers are in series, the first several
have highest loads and those toward the
end have progressively smaller loads.
Air venting: an important requirement during
startup when drums or cylinders contain large
amounts of air.
Shock, vibration and water hammer: usually
come from return systems or improperly
trapped steam supply. Faulty or broken
syphons can produce shocks.
Dirt and corrosion: can be a significant factor
and is related to frequency of startups.
Recommended traps
Desired characteristics: rugged, having hot
discharge and fast response. Ability to handle
flash steam by means of small bleed passage
is a necessity. Failure mode should be 'open'.
Installation tips: mount trap below cylinder.
If flexible hose is used, care should be taken
to assure it has an adequate bore and liner,
materials suitable for steam service.
Drainage to trap: syphon drainage is standard
practice. Condensate moving up the syphon
from the outer rim to the center of the drum
is subject to reheating and flashing-steam
binding of trap is common problem.
72
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
Equipment Type 4, Class A
Steam
A
Auxiliary
air vent
A
Dressing
sterilizer
Autoclave
Steam heats a solid directly
Typical equipment:
• Reaction chamber
• Retort
• Pressure cooker
Activity: heating a material or producing a
chemical reaction in an enclosed pressure
vessel, by direct exposure to live steam.
Condensate forms on product surfaces.
Steam pressures: range from 15 to 150 psi
with 15 to 50 being most typical. When
the process is temperature controlled,
steam temperatures can vary. On startup,
pressures may be unexpectedly low.
Condensate loads: can be very large on startup
and quite low after temperature is reached.
Drainage to trap: must be gravity drainage
with trap well below equipment.
Discharge from trap: good condensate
drainage after the trap is especially important
in preventing contamination due to flooding.
Ambient conditions: equipment is usually in
a building and may be subject to generally hot
conditions.
Air venting: very important consideration due
to potentially large volumes involved. Separate
air vents are frequently used.
Shock, vibration and water hammer: shock
may be generated in the return system and
as a result of condensate forming in slugs.
Dirt and corrosion: may be a problem because
condensate can be contaminated from
contact with material being heated. Because
of frequent startups and exposure to air,
corrosion problems can be expected.
Recommended traps
Desired characteristics: fail open and self
draining desirable. Hot discharge and fast
response with good air handling a must.
Good dirt handling especially required in
some applications.
Installation tips: place strainer (extra large
where contamination is heavy) with blowdown
valve ahead of trap and position for frequent
servicing. Good drainage after trap is
especially important with outdoor installations
where freeze-up can be a problem. Bellows
thermostatic trap mounted in vertical-up
position is a good auxiliary air vent.
73
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
How to trap steam mains
Recommended drip
pocket diameter and
length
Activity: removal of condensate from steam
mains to protect steam equipment, prevent
water hammer and maintain steam quality
between boiler and point of use.
Steam pressures: generally constant with
some seasonal variation. Typical industrial
pressures 100-600 psi. Utilities, pulp and paper,
and chemical plants frequently higher.
Condensate loads: usually small and constant,
10 to 50 lb/hr per trap station except during
startup when loads can be quite heavy. Larger
at ends of mains especially if earlier trapping
has been inadequate.
Drainage to trap: most commonly by gravity
with trap below steam main. Occasionally
piping in trenches will require lift fitting from
a collector when trap is above main.
Discharge from trap: commonly to closed and
pressurized return systems but also to open
atmospheric drains.
Ambient conditions: vary widely. Range from
underground tunnels to outdoor exposure to
Arctic winters. Freezing is the most common
concern.
Air venting: need is minimal because startups
are infrequent. Some pipelines will have
manual valves as air vents at startup.
Shock, vibration and water hammer:
generally result from inadequate drainage of
condensate Moving at high velocity. Excessive
warm-up rates can produce thermal shocks
in return system. Also, negative pipe pitch and
inn properly located drip traps will produce
problems.
Dirt and corrosion: no unusual problems
beyond the oxides and dirt particles typical
of any steam system.
Recommended traps
Desired characteristics: fail open, self
draining, install in any position. Tolerant of
superheat. Capability of operating over wide
pressure ranges aids standardization.
Installation tips: use of a standard pipeline
'T' in main provides a drainage pocket so that
condensate can get to a trap. An extension to
'T' is sometimes used to increase its storage
volume. Strainers with blowdown valve and test
'T' are recommended in addition to standard
block valves for maintenance and checking.
74
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
How to estimate steam main condensate loads
Condensate load, C1
(Warming up)
lb/hr per 100 ft of pipe
Nominal pipe size
in
1
1½
2
3
4
6
8
10
12
14
16
18
20
24
10
14
22
30
60
93
166
250
315
337
416
478
536
605
721
100
16
25
35
69
99
185
277
352
419
461
532
596
673
802
Operating steam pressure, psi
200
300
400
17
19
19
27
30
32
38
40
46
74
78
81
107
113
126
198
208
220
298
313
329
375
395
415
448
472
495
493
519
545
578
592
628
638
670
703
719
757
793
857
900
945
600
20
36
48
92
131
239
357
449
541
591
681
763
860
1024
1000
26
42
57
108
154
280
414
521
623
686
789
884
997
1189
600
13
19
24
35
45
66
87
108
128
141
161
181
202
242
1000
13
26
33
49
63
93
121
151
179
197
225
253
280
337
Assumed conditions:
Warm-up rate, 400°FExtra strong pipe
Ambient, 0 deg. °F
Wind, 0 MPH
Insulation 85% eff.
10% additional load for warming insulation
50% of running load
Condensate load, C2
(Normal)
lb/hr per 100 ft of pipe
Nominal pipe size
in
1
1½
2
3
4
6
8
10
12
14
16
18
20
24
10
3
4
5
8
10
15
20
25
30
33
38
43
48
57
100
5
8
10
15
19
29
38
47
56
62
70
79
88
106
Operating steam pressure, psi
200
300
400
7
9
10
11
13
15
13
16
19
20
24
28
26
31
36
38
46
53
50
60
69
62
75
87
74
89
103
81
98
113
93
112
129
105
126
145
116
140
161
140
168
194
Assumed conditions:
Ambient. 0 deg. °F: insulation efficient. Saturated steam, zero (0) wind velocity; pipe surface
temperatures same as steam temperature.
Note: ambient temperature, wind and rain can influence loads.
Comments:
• Increasing ambient temperature from 0°F to 100°F will decrease condensate load
approximately 30%.
• Increasing wind velocity from 0 mph to 15 mph will increase condensate load
approximately 225%.
75
Yarway Industrial steam trapping handbook
Appendix A - How to trap process equipment
How to trap steam tracers
Tracer
Steam
Tracer
Steam
Process pipeline
Activity:
• Maintaining the temperature of process
material such as asphalt, sulfur, wax or other
chemicals to aid in handling by preventing
congealing, solidification or separation.
• Prevent water lines, safety showers, pumps,
valves, etc. from freeze-ups.
• Maintain uniform temperatures in and
around instruments.
Steam pressures: typically 75-400 psi when
tracing process materials, but 15-150 psi more
common in freeze protection applications.
Below 40 psi, condensate return problems
increase in closed system when pressure
differentials are not adequate for good
drainage.
Condensate loads: low (0-40 lb/hr) and
relatively steady, varying with seasonal
changes. Long tracing runs, poor insulation,
submerged lines can produce higher loads.
Drainage to trap: most frequently by gravity,
but lift drainage can be experienced when
tracing occurs below grade in trenches.
Discharge from trap: by gravity to open drains
or closed returns-some pressurized and
elevated.
Control valve
Air venting: of limited importance when
tracing process materials because of
infrequent startups. If startups are frequent
during seasonal changes, freeze protection
systems may have modest air venting needs.
Shock, vibration and water hammer:
a minimal problem.
Dirt and corrosion: generally modest in tracing
of process lines. Dirt can be a problem in freeze
protection systems due to corrosion products
in seasonally activated lines and light sluggish
condensate flows.
Recommended traps
Desired characteristics: fail open, selfdraining, small and lightweight as frequently
trap is not well supported. Easy checking is
helpful as many traps are installed.
Installation tips: when possible, locate traps
close together using condensate return
manifold. This also simplifies maintenance
and trap checking. Provide strainers, test 'T'
and suitable block valves. Assure adequate
pressure differential across trap for good
drainage when discharging to a closed and
elevated return system.
Ambient conditions: freezing is the main
concern. Most tracing is exposed to the
weather but is also used in unheated buildings.
76
Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Appendix B – Introduction
This section is intended for those particularly
interested in the laboratory testing technology
of steam traps. It recommends test methods
and procedures for use in making comparative
evaluations of steam traps.
Steam trap checking is the process of
determining in the field, whether or not a trap is
functioning properly. (Refer to Chapter 6, Steam
trap maintenance and troubleshooting). Steam
trap evaluation is the practice of quantifying
specific performance characteristics and
then making judgments about the trap’s
suitability for various types of service. This
requires the controlled conditions and precise
measurements of a qualified laboratory.
Evaluation criteria
Selecting the performance-related criteria
that should be evaluated requires a thorough
knowledge of the specific needs of differing
steam trap applications. For example, process
traps and protection traps serve different needs
and should be evaluated accordingly. Five
important evaluation criteria can properly be
listed in different relative orders of importance,
depending on the intended service of the trap
being evaluated.
Protection (drip and tracer) traps
1.Steam loss
2.Back pressure limit
3.Predominant failure mode
4.Capacity
5.Air handling on startup
Process traps
1.Capacity
2.Air handling on startup
3.Predominant failure mode
4.Back pressure limit
5.Steam loss
While the relative significance of these various
criteria can be debated, it should be clear that
an evaluation program should be tailored to
specific application needs.
Criteria definitions
• Steam loss: the amount of saturated steam
discharged during successive condensate
removal operations expressed in pounds per
hour. A measure of trap efficiency.
• Capacity: the amount of condensate that
can be discharged continuously from a
trap in a given period of time and under
specific conditions or pressure differential
and condensate temperature expressed in
pounds per hour.
• Back pressure limit: back pressure limit is
the maximum amount of back pressure that
can be applied to the discharge side of the
trap without causing malfunction. (A decrease
in discharge capacity with increasing back
pressure is normal and not considered
a malfunction). Back pressure limits are
expressed as the ratio of back pressure to
supply pressure (in absolute units) expressed
as a percent.
• Failure mode: the manner in which a trap is
most likely to malfunction. It can be either
open or closed, depending on the specific
design.
• Air handling on startup: the capability
of steam trap to vent air and other noncondensable gases during cold startup
conditions. At the present time there is no
generally recognized expression for this term.
In its testing programs, Emerson expresses
air handling capability in terms of actual
cubic feet per hour passed under specific
conditions of inlet and differential pressures.
Evaluation philosophy
In order to obtain meaningful results, traps
should be tested under controlled conditions
that are typical of actual field installations.
A minimum of three (3) identical traps is
recommended for testing. This avoids basing
conclusions on a single unit that may not be
representative of the model being evaluated,
due to manufacturing or other variations.
Well established trap manufacturers usually
publish reliable technical information.
Unfortunately, the test conditions used are not
always clearly stated, making valid competitive
comparisons difficult, if not impossible.
Published catalog information should be used
with caution when employed for this purpose.
Evaluative judgments are improved
when comparisons between trap types
(thermodynamic, mechanical and thermostatic)
are made in addition to the comparisons
between traps of a common technology.
77
Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Steam loss – test method
Condensate discharge is collected from a
trap operating under specific and constant
conditions. Heat balance calculations
determine the amount of steam discharged
with the condensate. The test is referred
to as a calorimeter test. Constant and
controlled conditions for the duration of
the test are required to obtain meaningful
results. Atmospheric conditions such as
ambient temperature must remain constant
and error-causing influences such as drafts
must be avoided.
Figure B.2 shows a typical calorimeter testing
arrangement. Figure B.3 is a data sheet
showing the type of information required and
heat balance calculations used in determining
steam loss. It has been completed using test
data representative of a properly performing
thermodynamic disc trap.
A note of caution: there are practical limits
to the accuracy that can be achieved in
this steam loss test. The applicable code
(ANSI PTC 39.1) states: “The average result
from three consecutive tests must agree within
10 percent or 1 pound per hour, whichever is
greater”. Obviously energy efficiency judgments
concerning steam traps can not properly be
based on differences that are smaller than
the accuracy of the test itself.
Emerson standard test conditions
Emerson has established its own test
conditions for use when making comparative
evaluations of all types of traps:
1.Steam loss
• Protection traps: 100 psi supply, nominal
condensate load 10 lb/hr
• Process traps: 100 psi supply, nominal
condensate load at 10% of stated
condensate capacity at the same
operating pressure.
2. Capacity-all traps
• 100 psi supply.
• Traps that discharge near saturated
conditions should be tested within 5°F
of saturation temperature.
• Subcooled traps, usually thermostatic
types, have a capacity that varies with the
amount of condensate subcooling. These
traps should be tested using different
levels of condensate subcooling so that
their relationship between subcooling
and capacity can be properly established.
3. Back pressure limit-all traps
• 100 psi supply, condensate loads same
as steam loss test.
4. Air handling
• 100 psi supply, condensate loads same
as steam loss test.
5. Characteristics such as failure mode
or freeze resistance can generally be
evaluated satisfactorily from published
data and technical analysis.
Figure B.2
Typical test arrangement for steam loss tests
Valve
5
Cooling water in
Valve
1
T1
Steam in
Temp.
in
Ps
Heat exchanger
Valve
2
Condensate drain
device trap
TL
Temp. out
Supply
press.
Ts
Supply
temp.
Valve
4
Valve
3
Test
trap
Vacuum
breaker
Slope
Agitator
To drain
Cooling water out
To drain
Vented cover
or plastic
balls
Wc
Calorimeter
tank
TFE
Scale
78
Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Test procedure
Start with all valves closed and tank empty
(reference Figure B.2).
1.Open valves 1, 2 and 3 to permit trap
draining steam inlet line and test trap
to operate at test pressure Ps.
2.During warm-up, weigh and record
weight of empty calorimeter tank Wt, and
record steam pressure Ps and steam
temperature Ts.
3.Open valves 5 and 6 to allow flow of cooling
water through heat exchanger to create
desired condensate load on test device.
Allow system to come to equilibrium.
4. Fill calorimeter tank with enough water
having a temperature T1 at least 15°F below
ambient temperature Ta to obtain a test run
of reasonable duration. Weight and record
water temperature T1 and weight of water
plus calorimeter tank, TL.
5.Rapidly close valve 3 and open valve 4. Start
timing interval when valve 4 is open. (Use of
a 3-way valve is recommended to facilitate
rapid closing and opening).
6.Agitate the water in the calorimeter tank
as necessary to ensure uniform water
temperature.
7. When the temperature of the water in the
calorimeter tank is as many degrees above
ambient as the initial temperature was
below, rapidly close valve 4 and open valve 3,
simultaneously recording the elapsed time,
then the final water temperature T2 , and
weight of water plus calorimeter tank, W2.
8.Enter data in the calorimeter test data
sheet and calculate steam loss. Refer to
steam tables Appendix D for enthalpy values
(i.e., sensible heat of liquid and latent heat
of evaporation) required by data sheet.
For reference, calorimeter test guidelines
are published in the ANSI/ASME PTC 39.1
performance test code for condensate removal
devices by the American Society of Mechanical
Engineers, United Engineering Center, 345 East
47th Street, New York, N.Y. 10017
Discharge capacity – test method
Condensate discharge capacity of steam traps
varies with each type and make. Interest is
directed to two distinct flow rates: (1) cold
condensate capacity for startups; and (2) hot
condensate capacity that will be available in
the actual installation.
For on-off type traps that discharge near
steam temperature, usually thermodynamic
and mechanical traps, the discharge capacity
is primarily a function of differential pressure
and is proportional to the square root of
differential pressure. (For estimating purposes,
the steam temperature discharge capacity is
approximately ⅓ of the cold water capacity
due to the choking effects of flash steam
and changes in liquid density.)
For certain modulating traps (usually bimetallic
thermostatic type traps), the discharge capacity
is a function of both differential pressure
and temperature. The discharge capacity
will increase with increasing amounts of
condensate subcooling until the maximum
capacity is reached. Capacity data for a
modulating type trap must reference both
temperature and pressure.
Typical condensate capacity discharge curves
are presented in Figures B.4 and B.5. their
different form results from the different
operating principles of the traps being tested.
79
Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Figure B.3
Yarway calorimeter test data
Yarway calorimeter test data
Trap type:
Age and service:
Data recorded by:
P
Pa
Yarway 720 A
1 year, 150 psi drip
D. Kalix
Log #:
Date:
Test station:
Trap number:
1
Run number:
1
100.00
Size: ½”
Nominal steam test pressure (psig)
Barometric pressure (psia) 1 in. Hg. = .4914 psia
Inlet steam pressure (psia)
Inlet steam temperature (°F)
Enthalpy of saturated liquid at Ts (BTU/Ibm)
Latent heat of evaporation at Ts (BTU/Ibm)
Weight of container (Ibm)
Equiv. water weight of container = *Wc x .225 (Ibm)
Weight of initial water + container (Ibm)
Ambient temperature (°F)
Initial temperature of water (°F)
Enthalpy of water initially at T1 (BTU/Ibm)
Weight of final water plus container (Ibm)
Final temperature of water and condensate (°F)
Enthalpy of water finally at T2 (BTU/Ibm)
Time of test (seconds)
Weight added to scale = W2 – W1 (Ibm)
Initial total enthalpy = (W1 – Wc+ We)Hf1
= (W1 – 12.75)Hf1 (BTU)
Final total enthalpy = (W2 – Wc + We)Hf2
E2
= (W2 – 12.75)Hf2 (BTU)
E2 – E1 BTU provided by discharge (lbm/hr)
Es
Discharge enthalpy of saturated water = Hfs x ØW
Total discharge = ØW x 3600/Øt (lbm/hr)
Steam loss = WL = (E2 – E1) – Es x 3600 (lbm/hr)
Hfgs
Øt
Ps
Ts
Hfs
Hfgs
Wc
We
W1
Ta
T1
Hf1
W2
T2
Hf2
Øt
ØW
E1
Cycles/minute:
Back pressure limit:
Discharge temperature (°F):
0973
18 May 1983
5
1
1
2
3
100.00
100.00
15.00
115.00
338.00
309.10
880.60
15.45
2.70
40.70
70.00
59.10
27.16
42.95
81.00
49.02
596.00
2.25
759.00
15.00
115.00
338.00
309.10
880.60
15.45
2.70
40.70
69.00
60.50
28.56
45.95
78.00
46.02
560.00
2.10
888.00
15.00
115.00
338.00
309.10
880.60
15.45
2.70
40.70
68.00
58.80
26.86
43.20
78.00
46.02
512.00
1.95
766.00
1480.00
1528.00
1401.00
721.00
695.00
13.60
0.20
640.00
649.00
13.50
-
635.00
603.00
13.70
0.30
5.00
336.00
3.00
336.00
4.00
337.00
Notes
Back pressure limit test not performed
* Excludes weight of nipples and valve
80
Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Figure B.4
Condensate capacity near steam temperature (typical for on-off type traps)
0.1
0.2
0.3
0.5
1
2
3
5
10
20
30
5000
10,000
9,000
8,000
7,000
6,000
5,000
3000
2000
4,000
Req. trap flow rate, lb/hr
3,000
1000
2,000
700
500
1,000
900
800
700
600
500
300
200
400
300
100
200
70
50
100
90
80
70
60
50
30
1
2
3
4
5 6 7 8 9 10
20
30
40 50 60 80100 200
300
400 500 600
Trap inlet pressure, psi
Figure B.5
Condensate capacity vs discharge temperature (typical for subcooled thermostatic traps)
Trap flow rate kg/hr
Saturation
temperature
50
100
200
300
400
25
50
50
100
75
150
50 psi
100 psi
200 psi
300 psi
200
0
200
400
600
800
Subcooling °C
Subcooling °F
0
100
1000
Trap flow rate lb/hr
81
Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Discharge capacity test procedure
(dynamic weight method)
Start with all valves closed (reference
Figure B.6).
1.Open valves 1 and 2 and fill accumulator
tank to desired level. Close valve 1.
2.Open valve 3 and heat water in accumulator
tank to desired temperature. Close valves 2
and 3 and open valve 4.
3. Fill barrel approximately half full of cold
water. The end of the discharge pipe should
be under water in the weigh tank. Balance
scale lever arm, then add an appropriate
weight to allow time for opening and
closing valves.
4.Open valves 5 and 6 to heat pipe and test
trap.
5. When thermal equilibrium is reached,
close valve 6 and open valve 7.
6. When scale lever arm is balanced, start
timing and add an appropriate weight to
the yoke corresponding to the number of
pounds of condensate to be collected. This
should be less than the amount necessary
to cause boiling of the water in the
weigh tank.
7. When scale lever arm is again balanced,
stop timing and close valve 5.
8.Observe and record the following data:
a.Elapsed time
b.Ambient temperature Ta (°F)
c.Barometric pressure, Pa (psia)
d.Steam pressure and temperature,
Ps (psig) and Ts (°F)
e.Weight of condensate plus barrel at
start and finish, We (lb)
f. Initial and final values of the following:
(i)Temperature differential (T5 – Tcl °F)
(ii) Inlet pressure, P1 (psig)
(iii)Back pressure, P2 (psig)
9. Calculate capacity in lb/hr.
Discharge capacity test guidelines are
published in ANSI/ASME PTC 39.1 performance
test code for condensate removal devices.
Back pressure – test method
At the present time there is no generally
accepted standard procedure for performing
back pressure tests. Experience has shown that
back pressure limitations can be determined
easily by installing a trap into a test rig having
controlled inlet conditions, and with an outlet
connected to a receiving tank, whose pressure
can be regulated, to simulate a closed return
system. Either steam or air may be used to
pressurize the tank. Assure its pressure rating
is adequate for the test. This test is usually
performed on thermodynamic traps.
Figure B.6
Typical arrangement for discharge capacity testing (dynamic weight method)
Safety
valve
Vent
Supply
press
Ps
Pressure
reducing
valve
Valve
2
Valve
4
Ts
Valve
1
Cold water
Accumulator
Note 2
Press
Gauge
P1
glass
Tc
Steam
supply
Circulation
Valve
3
Injector line
Valve
5
Press
P2
Valve
7 Slope
Test trap
Valve
6
Temp.
condensate
Scale
Open pit
Vacuum
breaker
Barrel
Notes
1.The piping from the accumulator to the test
device shall be of the same diameter as the
inlet connection on the test device. The inlet to
the piping from the accumulator shall be in the
form of a well rounded entrance.
2.The distance between the sensors and the test
device shall not exceed 20 internal pipe diameters.
82
Yarway Industrial steam trapping handbook
Appendix B - Steam trap evaluation methods
Test procedure (for trap closing limit)
1. Confirm normal operation of the trap
with a suitable listening device.
2.Gradually increase the back pressure in
steps of 5 psi, waiting approximately three
minutes after each adjustment to allow the
trap time to stabilize itself. Listen for the
opening and closing action.
3. When the trap stays open and stops
functioning, the back pressure limit has
been reached.
4. Confirm the limit by repeating the test 2
or 3 times.
Test procedure (for discharge temperature
reduction)
In a similar manner the effects of back
pressure on discharge temperature can be
established. Depending on the type and make
of trap, 40°F to 120°F reductions in discharge
temperature can result when subjecting it to
back pressures up to 80%.
1. Install the trap (usually a bimetallic
thermostatic trap) in the same system.
Provision to measure the inlet temperature
of the trap is required.
2.Allow 3 to 5 minutes for the trap to
stabilize itself before recording the inlet
temperature.
3. Increase back pressure in 5 psi increments.
Allow sufficient time for the trap to
stabilize its operations and the record inlet
temperature.
Repeat the process over the desired back
pressure testing range in order to establish
a complete profile of discharge temperature
reduction.
Note: in evaluating the effects of back
pressure on a steam trap, it is important that
the condensate flow not exceed the trap’s
capacity for the pressures involved.
'Flooding' of the trap will give erroneous
results.
Air handling capability – test method
Currently there is no generally recognized
test standard for evaluating a steam trap’s air
handling capability. Emerson has developed
a simple and reliable method for comparing
the relative air handling capabilities of various
types of traps. Figure B.7 is a schematic
representation of its air handling test
arrangement. The test requires the installation
of a trap in a steam line and allowing it
sufficient time to heat up and stabilize its
performance. Then a known volume of air is
injected (under supply pressure conditions)
into the supply line ahead of the trap.
The time required to discharge the air is then
measured. By comparing the times required
to remove the air, it is possible to rank various
types of traps according to their relative air
handling capability.
Test procedure
1.Allow temperatures of test trap and rig to
warm up by opening V-1, V-2, V-3 and V-4.
Normal steam pressure 100 psig, (338°F).
2.After temperatures have stabilized,
blowdown air cylinder by closing V-2, V-3
and opening V-5 and A-1. Blowdown until an
air temperature of 200°F is attained at T2.
3. Close V-4 and V-5 and pressurize the air
cylinder to 90 psig.
4.Open V-4 and V-2.
5. If using a recorder to measure temperature
at T1 start the recorder.
6.Shut V-1 and immediately open V-3. If using
a timer, start the timer.
7.Stop the timer when the inlet temperature
at T1 returns to normal operating
temperature.
Figure B.7
Steam trap air handling capability – test rig
Steam supply
V-2
T1
Pressure
V-1
Test trap
V-3
Drain
Pressure
V-6 (Drain)
Regulator
A-1
Air supply
Air cylinder
T2 Thermocouple
V-4
V-5 (Drain)
83
Yarway Industrial steam trapping handbook
Appendix C - Glossary of terms
Appendix C
Air binding: the process of a steam trap closing
due to the presence of air rather than steam.
This slows down the discharge of condensate
and the ability of a steam system to reach its
desired temperature (reference Chapter 5).
Flash steam: steam that results when
saturated water or condensate is discharged
to a lower pressure. It is steam that could
not exist at a higher pressure (reference
Chapter 2).
Blow-down valve: a valve used when
blowing pipeline dirt or scale from a strainer
screen or boiler drum (reference Chapter 5,
Figure 5.1).
Flash tank: a vessel or tank where flash steam
is accumulated for subsequent use (reference
Chapter 5, Figure 5.3).
British Thermal Unit (BTU): The quantity of
heat required to raise one pound of water
one (1) degree fahrenheit (reference Chapter 2).
Capacity: the maximum amount of condensate
that can be discharged by a steam trap
at specific conditions of temperature and
pressure differential (between its inlet and
outlet)-capacity is measured in pounds per
hour (reference Chapter 4).
Latent heat of vaporization: heat that
produces a change of state without a change
in temperature, such as changing water into
steam-sometimes referred to simply as 'latent
heat' (reference Chapter 2).
Modulate: the partial opening and closing of a
steam trap, thereby regulating the discharge
flow of condensate. Modulation is in contrast
to a full open/full closed mode of operation.
Condensate: the result of steam changing
from vapor to a liquid.
psia: pounds per square inch absolute-a
measure of pressure including atmospheric
pressure (about 14.69 psi).
Cycle: the opening and closing action of a
steam trap that allows it to pass condensate
and then stop the passage of steam.
psig: pounds per square inch gage – a measure
of pressure excluding atmospheric pressure
(about 14.69 psi).
Dirt pocket: a length of pipe in the discharge
line of steam heated equipment that allows the
collection (by gravity) of pipeline scale and dirt
(reference Figure 5.1).
Safety load factor: a factor, by which the
calculated condensate load is multiplied, to
determine the capacity a trap should possess
to properly serve its selected application. The
safety load factor is used to accommodate
system variables and uncertainties affecting
the condensate flow rate (reference Chapter 4).
Discharge temperature: the temperature
of condensate (measured at a steam trap’s
inlet) while it is being discharged. Sometimes
referred to as the temperature at which a
steam trap starts to open (reference Chapter 2
and Chapter 4).
Efficiency: see also ASME power test code
ANSI PTC39.1.
Enthalpy: the energy content of a fluid,
including both heat and mechanical energy,
BTU/lb-see Sensible, latent heat, and total
heat of steam.
Sizing: the process of matching the condensate
drainage requirements of an application
to a steam trap having a suitable capacity
(reference Chapter 4).
Saturated condensate: condensate that has
a temperature equal to that of the steam with
which it is in contact (reference Chapter 2).
Saturated steam: steam that has a
temperature equal to that of the condensate
with which it is in contact (reference Chapter 2).
84
Yarway Industrial steam trapping handbook
Appendix C - Glossary of terms
Saturation curve: graphic representation of
the boiling point of water at various pressures
(the pressure and temperature at which
saturated steam and condensate exist)
(reference Chapter 2).
Saturation temperature: the temperature at
which saturated steam and condensate exist
(reference Chapter 2, Figure 2.3).
Sensible heat: heat that produces a
temperature rise in a body (such as water)
(reference Chapter 2).
Steam:
• Dry: steam having no water droplets
suspended in it (reference Chapter 2).
• Live: 'live steam' is an expression commonly
used to describe steam that is still able to
do useful work-in contrast to flash steam
at atmospheric pressure.
• Wet: steam having fine water droplets
suspended in it, and as a result, having
a lower heat content than dry steam
(reference Chapter 2).
• Total heat of: the sum of BTUs per pound of
both the sensible heat (of condensate) and
the latent heat (of vaporization) (reference
Chapter 2).
Steam binding: the process of steam keeping
a steam trap closed and thereby preventing
the discharge of condensate that has formed
upstream of the trap. This condition results
when the condensate discharge line to a steam
trap is subjected to sufficient heating that the
condensate in it is changed back into steam,
thereby blocking the flow of condensate to
the trap (reference Chapter 5).
Steam separator: a device that removes
entrained water droplets from steam flow
(reference Chapter 5).
Steam tables: tables that list the properties
of steam and condensate at various pressures
and temperatures (reference Chapter 2).
Steam tracing: the use of steam to: (1) heat
or maintain the temperature of a process
liquid in a pipeline, (2) prevent water lines and
related equipment from winter freeze-ups,
and (3) provide uniform temperature in and
around instruments so as to help maintain
their calibration (reference Appendix A-11).
Steam trap: a self-contained valve which
automatically drains condensate and
discharges air and non-condensible gases
from a steam-containing pipe or vessel
(reference Chapter 3).
• Cool: a steam trap that discharges
condensate at temperatures significantly
below saturation temperature is referred
to as a 'cool trap' even though it may be at
a temperature well above 212°F (reference
Chapter 4).
• Hot: a steam trap that discharges condensate
at temperatures up to 10 degrees below
saturation temperature (reference Chapter 4).
• Process: a steam trap that discharges
condensate from equipment used in the
heating or production of some product
as distinct from a 'protection service'
application.
• Protection: a steam trap that discharges
condensate from an application such as
a steam main (to protect it from water
hammer) or from a tracer application
providing protection from freezing.
Steam trap standard: a preferred type of
steam trap and piping configuration for
removing condensate from each designated
piece of equipment in a steam system.
Superheat: heat that is added to dry saturated
steam.
Subcooling: the temperature difference
between that of steam and the condensate
being discharged by a steam trap. This
subcooling or suppression will be at least
2 or 3 degrees and sometimes much more.
Certain applications benefit from steam
traps that discharge condensate with a small
amount of subcooling, while others will benefit
from a large amount of subcooling.
Suppression: (see 'Subcooling').
Water hammer: the shock created when
accumulated condensate is swept down a
pipeline at high velocities and is slammed into
valves, elbows, steam traps, or other fittings.
85
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Appendix D – Contents
Conversion factors�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������86
Temperature conversion tables��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������87
Steam tables (abbreviated)���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������89
Sensible heat of liquid�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������90
Properties of pipe������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������91
Heat transfer coefficients����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 92
Specific heats�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������94
Standard piping symbols�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������96
Conversion factors
Length
1 in = 25.4 mm
1 mm = .03937 in
1 ft = 30.48 em
1 m = 3.28083 ft
1 micron = .001 mm
Area
1 in2 = 6.4516 cm2
1 ft2 = 929.03 cm2
1 cm2 = 0.155 in2
1 cm2 = 0.0010764 ft2
Volume
1 in3 = 16.387 cm3
1 ft3 = 1728 in3
1 ft3 = 7.4805 U.S. gal
1 ft3 = 6.229 British gal
1 ft3 = 28.317 liters
1 U.S. gal = 0.1337 ft3
1 U.S. gal = 231 in3
1 U.S. gal = 3.785 liters
1 British gal = 1.20094 U.S. gal
1 British gal = 277.3 in3
1 British gal = 4.546 liters
1 liter = 61.023 in3
1 liter = 0.03531 ft3
1 liter = 0.2642 U.S. gal
Velocity
1 ft per sec = 30.48 cm per sec
1 cm per sec = .032808 ft per sec
Weight
1 ounce av = 28.35 g
1 lb av = 453.59 g
1 gram = 0.03527 oz av
1 kg = 2.205 lb av
1 ft3 of water = 62.425 lb
1 U.S. gal of water = 8.33 lb
1 in3 of water = 0.0361 lb
1 British gal of water = 10.04 lb
1 ft3 of air at 60°F and 1 atm = 0.0764 lb
Flow
1 ft3 per sec = 448.83 gal per min
1 ft3 per sec = 1699.3 liters per min
1 U.S. gal per min = 0.002228 ft3 per sec
1 U.S. gal per min = 0.06308 liters per sec
1 cm3 per sec = 0.0021186 ft3 per min
Density
1 lb per ft3 = 16.018 kg per m3
1 lb per ft3 = .0005787 lb per in3
1 kg per m3 = 0.06243 lb per ft3
1 g per cm3 = 0.03613 lb per in3
Energy
1 BTU = 777.97 ft·lb
1 erg = 9.4805 x 10-11 BTU
1 erg = 7.3756 x 10-6 ft·lb
1 kilowatt hour = 2.655 x 106 ft·lb
1 kilowatt hour = 1.3410 hp hr
1 kg calorie = 3.968 BTU
Pressure
1 in of water = 0.03613 lb per in2
1 in of water = 0.07355 in of Hg
1 ft of water = 0.4335 lb per in2
1 ft of water = 0.88265 in of Hg
1 in of mercury = 0.49116 lb per in2
1 in of mercury = 13.596 in of water
1 in of mercury = 1.13299 ft of water
1 atmosphere = 14.696 lb per in2
1 atmosphere = 760 mm of Hg
1 atmosphere = 29.921 in of Hg
1 atmosphere = 33.899 ft of water
1 lb per in2 = 27.70 in of water
1 lb per in2 = 2.036 in of Hg
1 lb per in2 = .0703066 kg per cm2
1 kg per cm2 = 14.223 lb per in2
1 dyne per cm2 = .0000145 lb per in2
1 micron = .00001943 lb per in2
Power
1 horsepower = 33,000 ft·lb per min
1 horsepower = 550 ft·lb per sec
1 horsepower = 2,546.5 BTU per hr
1 horsepower = 745.7 watts
1 watt = 0.00134 horsepower
1 watt = 44.26 ft·lb per min
Viscosity
1 Centipoise = .000672 lb per ft sec
1 Centistoke = .00001076 ft2 per sec
Temperature
Temperature Fahrenheit (F) = 9/5 Celsius (C) + 32 = 9/4 R + 32
Temperature Celsius (C) = 5/9 Fahrenheit (F) – 32 = 5/4 R
Temperature Reaumur (R) = 4/9 Fahrenheit (F) – 32 = 4/5 C
Absolute temperature Celsius or Kelvin (K) = Degrees C + 273.16
Absolute temperature Fahrenheit or Rankine (R) = Degrees F + 459.69
Heat transfer
1 BTU per ft2 = .2712 g cal per cm2
1 g calorie per cm2 = 3.687 BTU per ft2
1 BTU per hr per ft2 per °F = 4.88 kg cal per hr per m2 per °C
1 kg cal per hr per m2 per °C = .205 BTU per hr per ft2 per °F
1 Boiler horsepower = 33479 BTU per hr
86
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Temperature conversion tables
C
-273.15
-268
-262
-257
-251
-246
-240
-234
-229
-223
-218
-212
-207
-201
-196
-190
-184
-179
-173
-169
-168
-162
-157
-151
-146
-140
-134
-129
-123
-118
-112
-107
-101
95.6
-90.0
-84.4
-78.9
-73.3
-67.8
-62.2
-56.7
-51.1
-45.6
-40.0
-34.4
-28.9
-23.3
-17.8
*
-459.67
-450
-440
430
-420
-410
-400
-390
-380
-370
-360
-350
-340
-330
-320
-310
-300
-290
-280
-273
-270
-260
-250
-240
-230
-220
-210
-200
-190
-180
-170
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
F
-459.4
-454
-436
-418
-400
-382
-364
-346
-328
-310
-292
-274
-256
-238
-220
-202
-184
-166
-148
-130
-112
-94
-76
-58
-40
-22
-4
14
32
C
-17.2
-16.7
-16.1
-15.6
-15.0
-14.4
-13.9
-13.3
-12.8
-12.2
-11.7
-11.1
-10.6
-10.0
-9.4
-8.9
-8.3
-7.8
-7.2
-6.7
-6.1
-5.6
-5.0
-4.4
-3.9
-3.3
-2.8
-2.2
-1.7
-1.1
-0.6
0.0
0.6
1.1
1.7
2.2
2.8
3.3
3.9
4.4
5.0
5.6
6.1
6.7
7.2
7.8
8.3
8.9
9.4
10.0
Fahrenheit and Celsius (Centigrade)
*
F
C
*
F
C
1
33.8 10.6
51 123.8
43
2
35.6 11.1
52 125.6
49
3
37.4 11.7
53 127.4
54
4
39.2 12.2
54 129.2
60
5
41.0 12.8
55 131.0
66
6
42.8 13.3
56 112.8
71
7
44.6 13.9
57 134.6
77
8
46.4 14.4
58 136.4
82
9
48.2 15.0
59 138.2
88
10
50.0 15.6
60 140.0
93
11
51.8 16.1
61 141.8
99
12
53.6 16.7
62 143.6
13
55.4 17.2
63 145.4
14
57.2 17.8
64 147.2
15
59.0 18.3
65 149.0
16
60.8 18.9
66 150.8 100
17
62.6 19.4
67 152.6
18
64.4 20.0
68 154.4
19
66.2 20.6
69 156.2
20
68.0 21.1
70 158.0
21
69.8 21.7
71 159.8
22
71.6 22.2
72 161.6 104
23
73.4 22.8
73 163.4 110
24
72.5 23.3
74 165.2 116
25
77.0 23.9
75 167.0 121
26
78.8 24.4
76 168.8 127
27
80.6 25.0
77 170.6 132
28
82.4 25.6
78 172.4 138
29
84.2 26.1
79 174.9 143
30
86.0 26.7
80 176.0 149
31
87.8 27.2
81 177.8 154
31
89.6 27.8
82 179.6 160
33
91.4 28.3
83 181.4 166
34
93.2 28.9
84 183.2 171
35
95.0 29.4
85 185.0 177
36
96.8 30.0
86 186.8 182
37
98.6 30.6
87 188.6 188
38 100.4 31.1
88 190.4 193
39 102.2 31.7
89 192.2 199
40 104.0 32.2
90 194.0 204
41 105.8 32.8
91 195.8 210
42 107.6 33.3
92 197.6 216
43 109.4 33.9
93 199.4 221
44 111.2 34.4
94 201.2 227
45 113.0 35.0
95 203.0 232
46 114.8 35.6
96 204.8 238
47 116.6 36.1
97 206.6 243
48 118.4 36.7
98 208.4 249
49 120.2 37.2
99 210.2 254
50 122.0 37.8 100 212.0 260
Interpolation values
*
110
120
130
140
150
160
170
180
190
200
210
212
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
F
230
248
266
284
302
320
338
356
374
392
410
413
428
446
464
482
500
518
536
554
572
590
608
626
644
662
680
698
716
734
752
770
788
806
824
842
860
878
896
914
932
C
266
271
277
282
288
293
299
304
310
316
321
327
332
338
343
349
354
360
366
371
377
382
388
393
399
404
410
416
421
427
432
438
443
449
454
460
466
471
477
482
488
493
499
504
510
516
521
527
532
538
*
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
810
820
830
840
850
860
870
880
890
900
910
920
930
940
950
960
970
980
990
1000
F
950
968
986
1004
1022
1040
1058
1076
1094
1112
1130
1148
1166
1184
1202
1220
1238
1256
1274
1292
1310
1328
1346
1364
1382
1400
1418
1436
1454
1472
1490
1508
1526
1544
1562
1580
1598
1616
1634
1652
1670
1688
1706
1724
1742
1760
1778
1796
1814
1832
C
0.56
1.11
1.67
2.22
2.78
*
1
2
3
4
5
F
1.8
3.6
5.4
7.2
9.0
C
3.33
3.89
4.44
5.00
5.56
*
6
7
8
9
10
F
10.8
12.6
14.4
16.2
18.0
* In the center column, find the temperature to be converted. The equivalent temperature is in the left column,
if converting to Celsius, and in the right column, if converting to Fahrenheit.
87
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Temperature conversion tables (continued)
C
543
549
554
560
566
571
577
582
588
593
599
604
610
616
621
627
632
638
643
649
654
660
666
671
677
682
688
693
699
704
710
716
721
727
732
738
743
749
754
760
766
771
777
782
788
793
799
804
810
816
*
1010
1020
1030
1040
1050
1060
1070
1080
1090
1100
1110
1120
1130
1140
1150
1160
1170
1180
1190
1200
1210
1220
1230
1240
1250
1260
1270
1280
1290
1300
1310
1320
1330
1340
1350
1360
1370
1380
1390
1400
1410
1420
1430
1440
1450
1460
1470
1480
1490
1500
F
1850
1868
1886
1904
1922
1940
1958
1976
1994
2012
2030
2048
2066
2084
2102
2120
2138
2156
2174
2192
2210
2228
2246
2264
2282
2300
2318
2336
2354
2372
2390
2408
2426
2444
2462
2480
2498
2516
2534
2552
2570
2588
2606
2624
2642
2660
2678
2696
2714
2732
C
821
827
832
838
843
849
854
860
866
871
877
882
888
893
899
904
910
916
921
927
932
938
943
949
954
960
966
971
977
982
988
993
999
1004
1010
1016
1021
1027
1032
1038
1043
1049
1054
1060
1066
1071
1077
1082
1088
1093
Fahrenheit and Celsius (Centigrade)
*
F
C
*
1510
2750
1099
2010
1520
2768
1104
2020
1530
2786
1110
2030
1540
2804
1116
2040
1550
2822
1121
2050
1560
2840
1127
2060
1570
2858
1132
2070
1580
2876
1138
2080
1590
2894
1143
2090
1600
2912
1149
2100
1610
2930
1154
2110
1620
2948
1160
2120
1630
2966
1166
2130
1640
2984
1171
2140
1650
3002
1177
2150
1660
3020
1182
2160
1670
3038
1188
2170
1680
3056
1193
2180
1690
3074
1199
2190
1700
3092
1204
2200
1710
3110
1210
2210
1720
3128
1216
2220
1730
3146
1221
2230
1740
3164
1227
2240
1750
3182
1232
2250
1760
3200
1238
2260
1770
3218
1243
2270
1780
3236
1249
2280
1790
3254
1254
2290
1800
3272
1260
2300
1810
3290
1266
2310
1820
3308
1271
2320
1830
3326
1277
2330
1840
3344
1282
2340
1850
3362
1288
2350
1860
3380
1293
2360
1870
3398
1299
2370
1880
3416
1304
2380
1890
3434
1310
2390
1900
3452
1316
2400
1910
3470
1321
2410
1920
3488
1327
2420
1930
3506
1332
2430
1940
3524
1338
2440
1950
3542
1343
2450
1960
3560
1349
2460
1970
3578
1354
2470
1980
3596
1360
2480
1990
3614
1366
2490
2000
3632
1371
2500
F
3650
3668
3686
3704
3722
3740
3758
3776
3794
3812
3830
3848
3866
3884
3902
3920
3938
3956
3974
3992
4010
4028
4046
4064
4082
4100
4118
4136
4154
4172
4190
4208
4226
4244
4262
4280
4298
4316
4334
4352
4370
4388
4406
4424
4442
4460
4478
4496
4514
4532
C
1377
1382
1388
1393
1399
1404
1410
1416
1421
1427
1432
1438
1443
1449
1454
1460
1466
1471
1477
1482
1488
1493
1499
1504
1510
1516
1521
1527
1532
1538
1543
1549
1554
1560
1566
1571
1577
1582
1588
1593
1599
1604
1610
1616
1621
1627
1632
1638
1643
1649
*
2510
2520
2530
2540
2550
2560
2570
2580
2590
2600
2610
2620
2630
2640
2650
2660
2670
2680
2690
2700
2710
2720
2730
2740
2750
2760
2770
2780
2790
2800
2810
2820
2830
2840
2850
2860
2870
2880
2890
2900
2910
2920
2930
2940
2950
2960
2970
2980
2990
3000
F
4550
4568
4586
4604
4622
4640
4658
4676
4694
4712
4730
4748
4766
4784
4802
4820
4838
4856
4874
4892
4910
4928
4946
4964
4982
5000
5018
5036
5054
5072
5090
5108
5126
5144
5162
5180
5198
5216
5234
5252
5270
5288
5306
5324
5342
5360
5378
5396
5414
5432
Temperature conversion formulas
Degrees Celsius
(formerly Centigrade °C)
°C + 273.15 = °K Kelvin
(°C x %) + 32 = °F Fahrenheit
°C x o/s = °R Reaumur
Degrees Fahrenheit - ° F
°F + 459.67 = °Rankine
(°F – 32) x % = °C Celsius
(°F – 32) x % = °R Reaumur
Degrees Reaumur - °R
°R x % = °C Celsius
(°R x %) + = °F Fahrenheit
88
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Steam tables
Steam
pressure
psig
28*
26*
24*
22*
20*
18*
16*
14*
12*
10*
8*
6*
4*
2*
0*
1
2
3
4
5
6
7
8
9
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
110
120
125
130
140
150
160
170
180
190
Steam
temperature
°F
101
126
141
152
162
169
176
182
187
192
197
201
205
209
212
216
219
222
224
227
230
232
235
237
240
250
259
267
274
281
287
292
298
303
307
312
316
320
324
328
331
335
338
344
350
353
356
361
366
371
375
380
384
Heat BTU/lb
Sensible
60
93
109
120
130
137
144
150
155
160
165
169
173
177
180
183
187
190
193
195
198
201
203
206
208
218
227
236
243
250
256
262
267
272
277
282
286
290
294
298
302
306
309
316
322
325
328
334
339
344
348
353
358
Latent
1037
1023
1014
1007
1001
997
993
989
986
983
980
977
975
972
970
968
965
964
962
961
959
957
956
954
952
945
940
934
929
924
920
915
912
908
905
901
898
895
892
889
886
883
881
876
871
868
866
861
857
853
849
845
841
Total heat
of steam
1105
1116
1122
1127
1131
1134
1137
1139
1141
1143
1145
1146
1148
1149
1150
1151
1152
1154
1155
1156
1157
1158
1159
1160
1160
1163
1167
1170
1172
1174
1176
1177
1179
1180
1182
1183
1184
1185
1186
1187
1188
1189
1190
1192
1193
1193
1194
1195
1196
1197
1197
1198
1199
Specific volume
ft3·lb
Saturated steam
339.0
177.0
121.0
92.0
75.0
63.0
55.0
48.0
43.0
39.0
36.0
33.0
31.0
29.0
27.0
25.0
24.0
22.5
21.0
20.0
19.5
18.5
18.0
17.0
16.5
14.0
12.0
10.5
9.5
8.5
8.0
7.0
6.7
6.2
5.8
5.5
5.2
4.9
4.7
4.4
4.2
4.0
3.9
3.6
3.3
3.2
3.1
2.9
2.7
2.6
2.5
2.3
2.2
* Vacuum in Mercury
89
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Steam tables (continued)
Steam
pressure
psig
200
220
240
250
260
280
300
350
400
450
500
600
750
1100
1450
1800
2200
2600
3000
3193
Steam
temperature
°F
388
395
403
406
409
416
422
436
448
460
470
489
513
558
593
622
650
675
696
705
Heat BTU/lb
Sensible
362
370
378
381
385
392
399
414
428
441
453
475
503
560
607
650
697
746
805
906
Latent
837
830
823
820
817
811
805
790
776
764
751
728
697
629
565
501
424
334
211
0
Total heat
of steam
1199
1200
1201
1201
1202
1203
1204
1204
1204
1205
1204
1203
1200
1189
1172
1151
1121
1080
1016
906
Specific volume
ft3·lb
Saturated steam
2.10
2.00
1.80
1.75
1.70
1.60
1.50
1.30
1.10
1.00
0.90
0.75
0.45
0.39
0.29
0.22
0.16
0.12
0.08
0.05
To facilitate steam trap calculations, values are rounded to the values shown.
Superheated steam
Steam
pressure
psig
200
400
600
1100
2200
3193
Saturated steam
Total heat of
Temperature
saturated steam
°F
BTU/lb
388
1199
448
1204
489
1203
558
1189
650
1121
705
906
Total temperature, °F
400
600
800
1000
Total heat of superheated steam BTU/lb
1207
1322
1425
1529
1306
1416
1523
1289
1408
1517
1235
1384
1502
1323
1467
1250
1432
To facilitate steam trap calculations, values are rounded to the values shown.
Sensible heat of liquid (btu/lb)
Temperature
°F
32
34
36
38
40
42
44
46
48
50
52
54
56
58
60
62
64
66
Sensible heat
(BTU/lb)
0.00
2.02
4.03
6.04
8.05
10.05
12.06
14.06
16.07
18.07
20.07
22.07
24.06
26.06
28.06
30.05
32.05
34.05
Temperature
°F
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
Sensible heat
(BTU/lb)
36.04
38.04
40.04
42.03
44.03
46.02
48.02
50.01
52.01
54.00
56.00
57.99
59.99
61.98
63.98
65.97
67.97
90
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Properties of pipe - Schedule 40 pipe dimensions
Diameters, in
Size
in
⅛
¼
⅜
½
¾
1
1¼
1½
2
2½
3
3½
4
5
6
8
10
12
14
16
18
20
24
External
.405
.540
.675
.840
1.050
1.315
1.660
1.900
2.375
2.875
3.500
4.000
4.500
5.563
6.625
8.625
10.750
12.750
14.000
16.000
18.000
20.000
24.000
Internal
.269
.364
.493
.622
.824
1.049
1.380
1.610
2.067
2.469
3.068
3.548
4.026
5.047
6.065
7.981
10.020
11.938
13.125
15.000
16.874
18.814
22.626
Metal
.072
.125
.167
.250
.333
.494
.669
.799
1.075
1.704
2.228
2.680
3.174
4.300
5.561
8.399
11.900
15.740
18.640
24.350
30.850
36.150
50.300
Length of pipe per ft2 of
Ext. surface
Int. surface
feet
feet
9.431
14.199
7.073
10.493
5.658
7.747
4.547
6.141
3.637
4.635
2.904
3.641
2.301
2.767
2.010
2.372
1.608
1.847
1.328
1.547
1.091
1.245
.954
1.076
.848
.948
.686
.756
.576
.629
.442
.478
.355
.381
.299
.318
.272
.280
.238
.254
.212
.226
.191
.203
.159
.169
Metal
.093
.157
.217
.320
.433
.639
.881
1.068
1.477
2.254
3.016
3.678
4.407
6.112
8.300
12.760
18.920
26.000
31.220
40.130
50.610
61.430
87.180
Length of pipe per ft2 of
Ext. surface
Int. surface
feet
feet
9.431
17.750
7.073
12.650
5.658
9.030
4.547
7.000
3.637
5.150
2.904
3.995
2.301
2.990
2.010
2.542
1.608
1.970
1.328
1.645
1.091
1.317
.954
1.135
.848
.995
.686
.792
.576
.673
.442
.501
.355
.400
.299
.336
.272
.306
.238
.263
.212
.237
.191
.208
.159
.177
Transverse areas, in
Nom.
thick., in
.068
.088
.091
.109
.113
.133
.140
.145
.154
.203
.216
.226
.237
.258
.280
.322
.365
.406
.437
.500
.563
.593
.687
External
.129
.229
.358
.554
.866
1.358
2.164
2.835
4.430
6.492
9.621
12.560
15.900
24.300
34.470
58.420
90.760
127.640
153.940
201.050
254.850
314.150
452.400
Internal
.057
.104
.191
.304
.533
.864
1.495
2.036
3.355
4.788
7.393
9.886
12.730
20.000
28.890
50.020
78.850
111.900
135.300
176.700
224.000
278.000
402.100
Properties of pipe - Schedule 80 pipe dimensions
Diameters, in
Size
in
⅛
¼
⅜
½
¾
1
1¼
1½
2
2½
3
3½
4
5
6
8
10
12
14
16
18
20
24
External
.405
.540
.675
.840
1.050
1.315
1.660
1.900
2.375
2.875
3.500
4.000
4.500
5.563
6.625
8.625
10.750
12.750
14.000
16.000
18.000
20.000
24.000
Internal
.215
.302
.423
.546
.742
.957
1.278
1.500
1.939
2.323
2.900
3.364
3.826
4.813
5.761
7.625
9.564
11.376
12.500
14.314
16.126
17.938
21.564
Transverse areas, in
Nom.
thick., in
.095
.119
.126
.147
.154
.179
.191
.200
.218
.276
.300
.318
.337
.375
.432
.500
.593
.687
.750
.843
.937
1.031
1.218
External
.129
.229
.358
.554
.866
1.358
2.164
2.835
4.430
6.492
9.621
12.560
15.900
24.300
34.470
58.420
90.760
127.640
153.940
201.050
254.850
314.150
452.400
Internal
.036
.072
.141
.234
.433
.719
1.283
1.767
2.953
4.238
6.605
8.888
11.497
18.194
26.067
45.663
71.840
101.640
122.720
160.920
204.240
252.720
365.220
ft3 per ft of
pipe
.00039
.00072
.00133
.00211
.00370
.00600
.01039
.01414
.02330
.03325
.05134
.06866
.08840
.13890
.20060
.35520
.54760
.77630
.93540
1.22300
1.55500
1.92600
2.79300
ft3 per ft of
pipe
.00025
.00050
.00098
.00163
.00300
.00500
.00891
.01227
.02051
.02943
.04587
.06172
.07980
.12630
.18100
.31710
.49890
.70580
.85220
1.11700
1.41600
1.75500
2.53600
Wt per ft
lb
.244
.424
.567
.850
1.130
1.678
2.272
2.717
3.652
5.793
7.575
9.109
10.790
14.610
18.970
28.550
40.480
53.600
63.000
78.000
105.000
123.000
171.000
No. thrds per
in of screw
27
18
18
14
14
11½
11½
11½
11½
8
8
8
8
8
8
8
8
-
Wt per ft
lb
.314
.535
.738
1.000
1.470
2.170
3.000
3.650
5.020
7.660
10.300
12.500
14.900
20.800
28.600
43.400
64.400
88.600
107.000
137.000
171.000
209.000
297.000
No. thrds per
in of screw
27
18
18
14
14
11½
11½
11½
11½
8
8
8
8
8
8
8
8
-
91
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Overall heat transfer coefficients
The 'U' value, or overall heat transfer coefficient, represents the total BTU transmitted in one hour
for each square foot of heat transfer surface at a temperature difference of one degree Fahrenheit
(BTU/hr ft2 °F). 'U' values are the arithmetical result of experiments, research, tests, practice
and operations in controlled installations. Most 'U' values are given for bare metal heat transfer
surface in intimate contact with the product. In general, the 'U' value is relatively high when a) the
temperature of operation is high, b) there is mechanical circulation, c) surfaces are smooth and
clean, and d) the viscosity of the fluid is low. In the table below, two 'U' values, the low and high
values normally experienced in general practice, are given for several of the more common heat
transfer media/product applications.
Overall heat transfer coefficients
Service
Alphabetical
listing
Air
Anodize solution
Asphalt
Brine, salt
Fatty acid (tallow)
Molasses
Oil, heavy
Oil, medium
Paraffin wax
Phosphatizing
Free
convection
1-2
100-200
18-25
100-175
50-100
20-40
15-40
30-50
25-45
100-200
solution
Plating solution
Slurry, light
Syrup
Sugar solution
Sulphur, molten
Tar
Water
100-225
75-150
20-40
40-80
25-40
15-25
125-225
Saturated steam
Forced
convection
6-8
150-300
40-60
150-275
125-250
60-90
50-90
50-100
40-60
150-300
160-300
140-280
70-90
100-200
40-50
40-60
150-300
Clamp
on*
2
25-30
7-10
25-30
12-20
10-15
7-10
9-12
10-15
25-30
Free
convection
2-3
50-90
5-9
60-100
15-30
6-10
6-10
6-10
6-10
50-90
Water
Forced
convection
5-8
100-180
10-15
100-150
30-55
10-15
12-25
12-25
30-50
100-180
Clamp
on*
2
18-20
3-5
18-20
6-10
5-8
3-5
5-7
5-8
18-20
25-30
20-25
10-15
12-20
10-15
7-10
25-30
50-100
30-90
6-10
15-30
6-10
5-9
70-100
100-200
60-160
10-20
30-60
10-15
10-15
100-200
18-20
16-18
5-8
6-10
5-8
3-5
18-20
* All values except as noted by '*' are for immersion or integral installations.
Selection of the 'U' value should be on the conservative side and depends on the accuracy of data describing
the actual operating conditions and heat transfer characteristics of the product. 'U' value estimates should be
influenced by the following considerations: is the fluid thick or viscous? Will it precipitate or cling to the heat
transfer surface? What degree of fouling can be expected during the operating cycle?
Physical properties of gases
Material
Air
Ammonia
Chlorine
Nitrogen
Oxygen
Sulphur dioxide
Water, vapor (STM)
Density
0.075
0.048
0.020
0.073
0.083
0.183
-
Spec. heat at 60°F (BTU/lb °F)
0.24
0.52
0.12
0.25
0.23
0.16
0.45
92
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Physical properties of liquids and solids
State
L
L
S
S
L
L
L
L
L
S
L
L
L
L
L
L
L
L
L
S
L
S
S
L
Spec. grav.
at 60-70°F
1.05
0.81
2.64
1.30
0.84
1.24
1.19
1.15
0.95
1.20
1.00
1.11
0.81
0.89
0.96
0.86
0.60
1.09
1.26
2.25
1.05
0.90
0.80
Spec. heat
at 60°F (BTU/Ib °F)
0.48
0.60
0.23
0.22-0.40
0.41
0.69
0.79
0.39
0.47
0.35 at 105°F
0.63
0.58
0.47
0.43
0.40
0.65
0.53
0.89
0.58
0.20
0.75
0.50
0.70
0.47
Lard
Lead
Leather
Linseed oil
Magnesia 10%
Meat, fresh, avg.
Machine oil
Nickel, rolled
Nitric acid – 95%
Nitric acid – 20%
Olive oil
Paper
Paraffin, solid
Paraffin, melted
Petroleum
Phosphoric acid – 20%
Rubber goods
Sodium hydroxide – 50% caustic soda
S
S
S
L
S
S
L
S
L
L
L
S
S
L
L
L
S
L
0.92
11.36
0.86-1.02
0.93
0.21
0.93
8.66
1.50
1.12
0.93
0.93
0.86-0.91
0.90
0.87
1.11
1.50
1.53
0.64
0.031
0.36
0.44
0.27
0.70
0.40
0.50
0.81
0.47
0.45
0.62
0.69
0.51
0.85
1.0-2.0
0.78
Starch
Steel, mild at 70°F
Steel, mild at 160°F
Steel, stainless (300 Series)
Sucrose – 60% sugar syrup
Sucrose – 40% sugar syrup
Sugar, cane and beet
Sulphuric acid – 98%
Sulphuric acid – 60%
Sulphuric acid – 10%
Trichloroethylene
Turpentine, spirits of
Vegetables, fresh, avg.
Water, pure, 32°F
Water, sea
Wines, table, avg.
Wool
Zinc
S
S
S
S
L
L
S
L
L
L
L
L
S
L
L
L
S
S
1.53
7.90
8.00
8.00
1.29
1.18
1.66
1.84
1.50
1.14
1.62
0.86
1.00
1.03
1.03
1.32
7.04
0.11
0.16
0.12
0.74
0.66
0.30
0.35
0.52
0.84
0.22
0.42
0.92
1.00
0.94
0.90
0.33
0.10
Material
Acetic acid – 100%
Alcohol – ethyl 95%
Aluminum
Asphalt
Benzene
Brine (CaCl – 25%)
Brine (NaCl – 25%)
Chocolate mixture
Cotton seed oil
Coal tars
Dowtherm a
Ethylene glycol
Fuel oil #1 (Kerosene)
Fuel oil #3 (PS 200)
Fuel oil #6 (Bunker C)
Fatty acid
Gasoline
Glue (2 Pts H20,1 Pt dry glue)
Glycerin
Glass, pyrex
Hydrochloric acid – 10%
Ice
Ice cream
Kerosene
93
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Specific heats of foodstuffs
Product
Apples
Apricots, fresh
Artichokes
Asparagus
Avocados
Bananas
Barracuda
Bass
Beef, carcass
Beef, flank
Beef. loin
Beef, rib
Beef, round
Beef, rump
Beef, corned
Beer
Beets
Blackberries
Blueberries
Brains
Broccoli
Brussels sprouts
Butter
Butterfish
Cabbage
Candy
Carp
Carrots
Cauliflower
Celery
Chard
Cheese
Cherries. sour
Chicken, squab
Chicken, broilers
Chicken, fryers
Chicken. hens
Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.87
.42
.88
.43
.87
.42
.94
.45
.72
.37
.80
.40
.80
.40
.82
.41
.68
.48
.56
.32
.66
.35
.67
.36
.74
.38
.62
.34
.63
.34
.89
.90
.43
.87
.42
.87
.42
.84
.41
.92
.44
.88
.43
.65
.34
.77
.39
.94
.45
.93
.82
.41
.91
.44
.93
.44
.94
.45
.93
.44
.65
.88
.43
.80
.40
.77
.39
.74
.38
.65
.35
Product
Chicken, capons
Clams. meat only
Coconut, meat and milk
Coconut. milk only
Codfish
Cod Roe
Cowpeas, fresh
Cowpeas, dry
Crabs
Crab apples
Cranberries
Cream
Cucumber
Currants
Dandelion greens
Dates
Eels
Eggs
Eggplant
Endive
Figs, fresh
Figs. dried
Figs, candied
Flounders
Flour
Frog legs
Garlic
Gizzards
Goose
Gooseberry
Granadilla
Grapefruit
Grapes
Grape juice
Guavas
Guinea hen
Haddock
Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.88
.44
.84
.41
.68
.36
.95
.45
.86
.42
.76
.39
.73
.39
.28
.22
.84
.41
.85
.41
.90
.43
.90
.38
.97
.45
.97
.45
.88
.43
.20
.007
.77
.39
.76
.40
.94
.45
.95
.45
.82
.41
.39
.26
.37
.26
.86
.42
.38
.28
.88
.44
.79
.40
.78
.39
.61
.34
.86
.42
.84
.41
.91
.44
.86
.42
.82
.41
.86
.42
.75
.38
.85
.42
Product
Halibut
Herring, smoked
Horseradish, fresh
Horseradish, prepared
Ice cream
Kale
Kidneys
Kidney beans, dried
Kohlrabi
Kumquats
Lamb, carcass
Lamb, leg
Lamb, rib cut
Lamb, shoulder
Lard
Leeks
Lemons
Lemon juice
Lettuce
Lima beans
Limes
Lime juice
Lobsters
Loganberries
Loganberry juice
Milk, cow
Mushrooms, fresh
Mushrooms, dried
Muskmelons
Nectarines
Nuts
Olives, green
Onions
Onions, welsh
Oranges, fresh
Orange juice
Oysters
Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.80
.40
.71
.37
.79
.40
.88
.43
.74
.45
.89
.43
.81
.40
.28
.23
.92
.44
.85
.41
.73
.38
.71
.37
.61
.34
.67
.35
.54
.31
.91
.44
.91
.44
.92
.44
.96
.45
.73
.38
.89
.43
.93
.44
.82
.41
.86
.42
.91
.44
.94
.47
.93
.44
.30
.23
.94
.45
.86
.42
.28
.24
.80
.40
.90
.43
.91
.44
.90
.43
.89
.43
.84
.41
94
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Specific heats of foodstuffs (continued)
Product
Peaches, Georgia
Peaches, N. Carolina
Peaches, Maryland
Peaches, New Jersey
Peach juice, fresh
Pears, Bartlett
Pears, Beurre Bosc
Pears, dried
Peas, young
Peas, medium
Peas, old
Peas, split
Peppers, ripe
Perch
Persimmons
Pheasant
Pickerel
Pickles, sweet
Pickles, sour and dill
Pickles, sweet mixed
Pickles, sour mixed
Pig’s feet, pickled
Pike
Pineapple, fresh
Pineapple, sliced
Pineapple juice
Plums
Pomegranate
Pompano
Porgy
Pork, bacon
Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.87
.42
.89
.43
.90
.43
.91
.44
.89
.43
.89
.43
.85
.41
.39
.26
.85
.41
.81
.40
.88
.43
.28
.23
.91
.44
.82
.41
.72
.37
.75
.38
.84
.41
.82
.41
.96
.45
.78
.29
.95
.45
.50
.31
.84
.41
.88
.43
.82
.41
.90
.43
.89
.43
.85
.41
.77
.39
.81
.40
.36
.25
Product
Pork, ham
Pork, loin
Pork shoulder
Pork, spareribs
Pork, smoked ham
Pork, salted
Potatoes
Prickly pears
Prunes
Pumpkin
Quinces
Rabbit
Radishes
Raisins
Raspberries, black
Raspberries, red
Raspberry juice, black
Reindeer
Rhubarb
Rutabagas
Salmon
Sapote
Sauerkraut
Sausage, beef and pork
Sausage, bockwurst
Sausage, bologna
Sausage, Frankfurt
Sausage, salami
Sardines
Shrimp
Spanish mackerel
Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.62
.34
.66
.35
.59
.33
.62
.34
.65
.35
.31
.24
.82
.41
.91
.43
.81
.40
.92
.44
.88
.43
.76
.39
.95
.45
.39
.26
.85
.41
.89
.43
.91
.44
.73
.37
.96
.45
.91
.44
.71
.37
.73
.37
.93
.44
.56
.32
.71
.37
.71
.37
.69
.36
.45
.28
.77
.39
.83
.41
.73
.39
Product
Strawberries
String beans
Sturgeon, raw
Sugar apple, fresh
Sweet potatoes
Swordfish
Terrapin
Tomatoes
Tomato juice
Tongue, beef
Tongue, calf
Tongue, lamb
Tongue, pork
Tripe, beef
Tripe, pickled
Trout
Tuna
Turkey
Turnips
Turtle
Veal, flank
Veal, loin
Veal, rib
Veal, shank
Veal, quarter
Venison
Watercress
Watermelons
Whitefish
Wines
Yams
Specific heat BTU
per lb per °F
Above
Below
freezing
freezing
.95
.45
.91
.44
.83
.41
.79
.39
.75
.38
.80
.40
.80
.40
.95
.45
.95
.45
.74
.38
.79
.40
.76
.38
.74
.39
.83
.41
.89
.43
.82
.41
.76
.39
.67
.35
.93
.44
.84
.41
.65
.35
.75
.38
.73
.37
.77
.39
.74
.38
.78
.39
.95
.45
.94
.45
.76
.39
.90
.78
.39
95
Yarway Industrial steam trapping handbook
Appendix D - Useful tables
Piping symbols
Item
Symbol
Item
Bushing
Union
Cap
Valve – Check, angle
Cross
Valve – Check, straight
Elbow – 45°
Valve – Cock
Elbow – 90°
Valve – Diaphragm
Gauge – Pressure
P
Valve – Float
Gauge – Temperature
T
Valve – Gate, angle
Symbol
Orifice
Valve – Isolation, gate or ball
Plug – Pipe
Valve – Globe, angle
Pump – Centrifugal
Valve – Globe, straight
Reducer – Concentric
Air Vent
A
Reducer – Eccentric
Vacuum Breaker
VB
Steam Trap
Valve – Quick opening
Strainer
Valve – Safety
Tee
Valve – Solenoid
96
Yarway Industrial steam trapping handbook
97
Yarway Industrial steam trapping handbook
98
Yarway Industrial steam trapping handbook
99
Emerson Electric Co.
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