TB1-025 Steam Trap Operation and Troubleshooting - Chem-Aqua

TB1-025 Steam Trap Operation and Troubleshooting - Chem-Aqua
Steam Trap Operation and Troubleshooting
Technical Bulletin 1-025
Boiler Systems
Updated 11/01/11
Steam Traps
Steam traps are devices that automatically discharge condensate and non-condensable gases from steam lines
and heat exchangers while retaining live steam. They can be located before and/or after heat exchange processes,
on the main steam header, and along horizontal runs of steam lines. Steam traps have three important functions



Promptly evacuate the condensate that forms when steam gives up its heat
Prevent the escape of live steam
Remove non-condensable gases, such as air and carbon dioxide
Properly installed and operating steam traps help improve the efficiency of a steam boiler system by keeping the
distribution lines and processes filled with dry steam, removing the non-condensable gases that can form an
insulating barrier on heat transfer surfaces and contribute to corrosion, and making hot condensate available for
recycling. Conversely, improperly installed and maintained steam traps reduce the efficiency of a steam boiler
system and increase operating costs. Steam traps can fail in either the open or closed position. Steam traps that
fail open allow live steam to pass, which wastes energy, water, and water treatment chemicals and increases
operating costs. Steam traps that fail closed will not properly evacuate condensate. The resulting buildup of
condensate causes steam lines and heat to become waterlogged, which prevents the flow of steam to the
processes being heated.
Types of Steam Traps
Steam traps are available in a variety of
designs that can offer advantages in
different applications. Three basic designs
are common.
Mechanical steam traps employ a bucket
or float that rises and falls based on the
condensate level in the trap. This rising
and falling is used to either open or close a
mechanical valve that allows condensate
to pass. The inverted bucket trap and the
float and thermostatic (F&T) trap are
common mechanical steam trap designs.
Inverted bucket traps are particularly
common due to their ruggedness and
ability to handle variable steam loads,
remove air and non-condensable gases at
steam temperatures, and resist water
hammer.
Thermostatic steam traps use a valve
that opens or closes in response to
temperature changes. In the presence of
steam, the thermostatic element expands,
which closes the trap and holds steam
back. When condensate forms and the
temperature drops below the steam
temperature, the thermostatic element
contracts, which opens the trap and allows
condensate to pass. These traps do not
handle water hammer very well. A
common type of thermostatic trap is based
on the expansion and contraction of a
bellows.
©2011 Chem-Aqua, Inc.
Closed – Holds Back Steam
Open – Dumping Condensate
Inverted Bucket Steam Trap Schematic*
Closed – Holds Back Steam
Open – Dumping Condensate
Thermostatic Bellows Steam Trap Schematic*
*Red is steam, blue is condensate
Above illustrations are copyright, remain the
Intellectual property of Armstrong International,
And are used with their kind permission.
Thermodynamic steam traps use a
disc that rises and falls based on the
variations in pressure that occur as
steam and condensate pass through the
trap. On startup, the pressure of the
incoming condensate raises the disc
allowing condensate to pass (Figure i).
As hot condensate flows through the
trap under the disc, flash steam forms to
create a low pressure area under the
disc that draws it toward the seat
(Figure ii). When the flash steam
pressure above the disc is greater than
the pressure underneath, the disc is
forced down to close the valve (Figure
iii). As the flash steam in the upper
chamber condenses, the pressure falls
causing the disc to be raised by the now
higher condensate pressure and the
cycle repeats (Figure iv).
Thermodynamic disc traps do not
handle variable loads or removal of air
and non-condensable gases very well.
However, they are very compact and
resist water hammer.
Thermodynamic Disc Steam Trap Schematic*
*Orange is steam, blue is condensate
Illustrations and text are taken from the Spirax Sarco website ‘Steam Engineering Tutorials’ at
http://www.spiraxsarco.com/resources/steam-engineering-tutorials.asp. Illustrations and text are
copyright, remain the intellectual property of Spirax Sarco, and are used with their kind
permission.
Troubleshooting Steam Traps
Malfunctioning steam traps can literally cost thousands of dollars per year in wasted steam, energy, water,
and treatment chemicals. Traps that fail open continuously pass steam into the condensate return system and
have the same impact as a steam leak.
You may be able to tell if a steam trap has failed open by visually inspecting the vent on condensate receivers
or feedwater tanks for the presence of flash steam. However, a steam trap survey using an ultrasonic steam
trap tester, infrared camera, or infrared temperature gun is a much more reliable way of identifying operational
problems. The cost of a routine steam trap survey is far outweighed by the operational savings associated
with reliable trap operation. Below is a table that shows the normal failure position for different types of steam
traps and how to tell if you have a failure.
Type of Steam
Trap
Float and
Thermostatic Trap
Inverted Bucket,
Thermodynamic
Disc, Thermostatic
Bellows Traps
**
Normal
Failure Mode
Open or Closed
Temperature
Upstream of Trap**
Temperature
Downstream of
Trap**
Operational Status
Hot
Intermittent
Hot and Cold
Normal
Hot
Hot (continuous
same temperature
as upstream of trap)
Steam Blowing by
Trap (Failed Open)
Cold
Cold
Condensate Flooding
the Steam Line
(Failed Closed)
Hot
Intermittent
Hot and Cold
Normal
Hot
Hot (continuous
same temperature
as upstream of trap
Steam Blowing by
Trap (Failed Open)
Open
Hot and cold are relative terms. Hot is as high as the steam temperature at a given pressure and cold can be as high at 200ºF.
©2011 Chem-Aqua, Inc.
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