Lecture 36
Learning Objectives
Upon completion of this chapter, Student should be able to
Explain the importance of fluid conditioners
List the major functions of filter and selection criteria
List application of the seven qualities of air as per ISO
Describe the function of various types of air regulators
List the function of FRL unit
Explain the various compressed air net work system
List the factors to be considered in selection of components for pneumatic network
Size the pipe diameter, pressure drop for a given pneumatic network
Operating instructions issued for pneumatic components almost always contain a note
recommending the installation of an air filter, pressure regulator and lubricator upstream of the
component. This is to ensure that only air which has been suitably conditioned will reach the
Air filter, pressure regulator and lubricator are now built as packaged combination known as
service units. Other than the impurities that might be entrained with the intake air and delivered
by the compressor air might pick up contaminants such as dust, scale or rust particles in the
distribution main leading to the take-off point. Provided that air main has been properly installed,
the major part of these impurities will collect in the condensate drain tanks. Minute particles
remain suspended in the air stream however and would damage the working parts of pneumatic
components by their abrasive action were they are removed beforehand. Furthermore the air flow
in the main pulsated, due, for one thing, to the compressor running intermittently as controlled by
pressure in air receiver. The consumer, on the other hand, need to work with a uniform air
pressure. Finally, lubrication is required for the moving parts of the pneumatic equipment.
The atmospheric air that is compressed in the compressor is obviously not clean because the
atmospheric air contains many contaminants line dirt , smoke water vapour etc. this
contaminated air lead to excessive wear and failure of pneumatic components. Therefore fluid
conditioners are used to supply clean dry and contamination free compressed air.
The purpose of the fluid conditioners is to make the compressed air more acceptable and suitable
fluid medium for the pneumatic system as well as the operating personal. The following five
fluid conditioners are used in pneumatic systems
1. Air Filters
2. Air Regulators
3. Air Lubricator
The purpose of the air filter is to clean the compressed air of all impurities and any condensate it
a) Function of air filters
To remove all foreign matter and allow dry and clean air flow without restriction to
regulator and then to the lubricator
To condensate and remove water from the air
To arrest fine particles and all solid contaminants from air
Filters are available in wide range starting from a fine mesh wire cloth (which strains heavy
foreign particles) to elements made of synthetic material (which removes very small particles)
Usually in line filter elements can remove contaminants in the 5-50 micron range.
b) Source of contamination.
Contaminants in a compressed air system can generally be attributed to the following:
The quality of air being drawn into the compressor: Air compressors draw in a large
volume of air from the surrounding atmosphere containing large numbers of airborne
The type and operation of the air compressor: The air compressor itself can also add
contamination, from wear particles to coolants and lubricants.
Compressed air storage devices and distribution systems: The air receiver and system piping
are designed to store and distribute the compressed air. As a consequence, they will also store
the large amounts of contaminants drawn into the system.
Additionally, piping and air receivers will also cool the moist compressed air forming condensate
which causes damage and corrosion.
c) Types of contamination in a compressed air system
Atmospheric dirt: Atmospheric air in an industrial environment typically contains 140
million per m3 of dirt particles. 80% of these particles are less than 2 microns in size and are
too small to be captured by the compressor intake filter, therefore passing directly into the
compressed air system
Water vapour, condensed water and water aerosols: Atmospheric air contains water vapour
(water in a gaseous form). The ability of compressed air to hold water vapour is dependent
upon it's temperature. The higher the temperature, the more water vapour that can be held by
the air. During compression, the air temperature is increased significantly, which allows it to
easily retain the incoming moisture. After the compression stage, air is normally cooled to a
usable temperature. This reduces the airs ability to retain water vapour, resulting in a
proportion of the water vapour being condensed into liquid water which is removed by a
condensate drain fitted to the compressor after-cooler. The air leaving the after-cooler is now
100% saturated with water vapour and any further cooling of the air will result in more water
vapour condensing into liquid water. Condensation occurs at various stages throughout the
system as the air is cooled further by the air receiver, piping and the expansion of valves,
cylinders, tools and machinery. The condensed water and water aerosols cause corrosion to
the storage and distribution system, damage production equipment and the end product. It
also reduces production efficiency and increases maintenance costs. Water in any form must
be removed to enable the system to run correctly and efficiently.
Rust and pipe scale: Rust and pipe scale can be found in air receivers and the piping of “wet
systems” (systems without adequate purification equipment) or systems which were operated
“wet” prior to purification being installed. Over time, this contamination breaks away to
cause damage or blockage in production which can also contaminate final product and
Micro-organisms: Bacteria and viruses will also be drawn into the compressed air system
the compressor intake and warm, moist air provides an ideal environment for the
growth of micro-organisms. If only a few micro-organisms were to enter a clean
environment, a sterile process or production system, enormous damage could be caused that
not only diminishes product quality, but may even render a product entirely unfit for use and
subject to recall.
Liquid oil and oil aerosols: Most air compressors use oil in the compression stage for
sealing, lubrication and cooling. During operation, lubricating oil is carried over into the
compressed air system as liquid oil and aerosols. This oil mixes with water vapour in the air
and is often very acidic, causing damage to the compressed air storage and distribution
system, production equipment and final product.
Oil vapour: In addition to dirt and water vapour, atmospheric air also contains oil in the
form of unburned hydrocarbons. The unburned hydrocarbons drawn into the compressor
intake as well as vaporized oil from the compression stage of a lubricated compressor will
carry over into a compressed air system where it can cool and condense, causing the same
contamination issues as liquid oil.
d) Factor affecting selection of filters
While selecting the filters, the following factors should be taken into account.
Size of particles to be filtered from the system
Capacity of the filter
Accessibility and maintainability
Life of the filter
Ability to drain the condensate
e) Construction
The construction of typical cartridge type filter along with graphical symbols is shown in Figure
1.1. It consists of filter cartridge, Deflector, bowl, water drain valve. Filter bowl is usually made
of plastic and transparent. For pressure more than 10 bar, bowl may be made of brass.
Figure 1.1 Construction of a Air filter.
f) Operation
Air enters the inlet port of the air filter through angled louvers. This causes the air to spin as it
enters the bowl. The centrifugal action of the rotating air causes the larger pieces of dirt and
water particles to be thrown against the inner wall of the filter bowl. These contaminants then
flow down into the bottom of the filter bowl.
A baffle prevents turbulent air from splashing water on to the filter element. The air, which has
been pre-cleaned in this way, then passes through the filter element, where the fine dirt particles
are filtered out. The size of the dirt particles which can be filtered out depends on mesh size of
filter element (usually 5-50 microns). The compressed air then exits through the outer port.
The pressure difference between inlet and outlet will indicate the degree to which the filter
element is clogged. Commercially available filters have many additional features like automatic
drain facility, coalescing type filter element, service life indicator etc.
g) Seven Quality levels of air required in production systems.
Figure 1.2 illustrates different levels of purity for various applications. Air from a compressor
passes through an after cooler with an auto drain to remove condensate. As the air cools further
in the air receiver more condensate is removed by an auto drain, installed on the bottom.
Additional drains may be fitted to all low points on the pipeline. The system divides into three
main parts:- Branches (1 and 2) provide air direct from the air receiver. Branches (3 – 6) use air
conditioned by a refrigerated type of dryer. Branch 7 incorporates an additional dryer of the
adsorption type. Standard filters in sub branches 1 and 2, equipped with auto drains remove
condensate; sub-branch 2 being higher purity because of the micro filter. Sub branches 3 – 5, use
refrigerated dry air, thus, branch 3 requires no auto drain, branch 4 needs no pre filtering and
branch 5 gives an improved level of air purity using a micro filter and sub micro filter, the
moisture having been removed by a refrigerated type of air dryer. Sub branch 6 incorporates an
odour removal filter. An adsorption type dryer eliminates all risk of condensation at low
temperatures in sub branch 7. Typical applications are listed in Table 1.1
Figure 1.2 Schematic Definition of 7 Degrees of Filtration
Table 1.1 Definition and typical applications of the seven qualities of air.
No. Removal of
Typical examples
Dust particles > 5 micron
solid Workshop air for clamping
Liquid oil to 99%
impurities humidify and blowing
Saturated humidity to 96%
oil can be accepted
Dust particles > 0.3 micron
Where removal of dust General industrial equipment,
Oil mist to 99.9%
and oil dominates, but a pneumatic
Saturated humidity to 99%
Humidity to atmosphere dew Where
point of -17
pneumatic drives
of drives,
be joints,
air tools
and air
of Similar to (1) as the air is dry
humidity is imperative additional spray painting
Dew point
but traces of fine dust
Saturated humidity to 99%
and oil are acceptable
Dust particles > 0.3 micron
Where no humidity, fine Process control, measuring
Oil mist to 99.9%
dust and oil vapour are equipment , high quality
Humidity up to an atmospheric acceptable
spray painting, cooling of
dew point of -17
moulding dies
Dust particles > 0.3 micron
, Pneumatic
Oil mist to 99.9999%
practically free from any measuring
Humidity up to an atmospheric impurity is required
electrostatic spray painting,
dew point of -17
electronic assemblies
As in (5) with odour removal
Where absolutely pure Pharmacy , food industry for
air, as under (5) but packaging , air transport,
odour free
All impurities as in (6) but with Where
brewing and breathing air
atmospheric dew point of greater condensation
than -30
of Drying
during components,
low pharmaceuticals,
be measuring
transport of powder.
h) Main Line Filter
A large capacity filter should be installed after the air receiver to remove contamination, oil
vapours from the compressor and water from the air. This filter must have a minimum pressure
drop and the capability to remove oil vapour from the compressor in order to avoid
emulsification with condensation in the line. It has no deflector, which requires a certain
minimum pressure drop to function properly A built-in or an attached auto drain will ensure a
regular discharge of accumulated water.
The filter is generally a quick change cartridge type. Figure 1.3 shows schematic diagram of
Main line filter.
Figure 1.3 Typical main line filter
a) Function: The function of the air pressure regulator is to maintain working pressure virtually
constant regardless of fluctuations of the line pressure and air consumption. When the pressure
is too low, it results in poor efficiencies and when the pressure is too high, energy is wasted and
equipment’s performance decay faster.
In pneumatic system, pressure fluctuations occur due to variation in supply pressure or load
pressure. It is therefore essential to regulate the pressure to match the requirement of load
regardless of variation in supply pressure or load pressure.
b) Where to regulate
Generally pressure is regulated in pneumatic system at two places.
At the receiver tank
In the load circuits
Pressure regulation at the receiver tank is required as a safety measure for the system. In the load
circuits, pressure regulator is used to regulate the pressure for downstream components such as
valves and actuators.
c) Types of Pressure regulator
There are two types of Pressure regulators
Diaphragm type regulator
Piston type regulator
Diaphragm type regulator is commonly used in Industrial pneumatic system. There are two
types of diaphragm type regulator
Non- reliving or non-venting type.
Relieving or venting type
Relieving or venting type is commonly used and is explained below. Relieving or Venting Type Pressure regulator
A Relieving type pressure regulator is shown in Figure 1.4, Outlet pressure is sensed by a
diaphragm preloaded with a adjustable pressure setting spring. The compressed air , which flows
through a controlled cross section at the valve seat, acts on the other side of the diaphragm. The
diaphragm has large surface area exposed to secondary (outlet) pressure and is quite sensitive to
its fluctuations. The movement of diaphragm regulates the pressure.
Figure 1.4 venting type pressure regulator
If the outlet pressure is low: whenever the more compressed air is consumed on secondary side
or load side, then load pressure reduces. Therefore less force acts on diaphragm. The opposing
higher spring force pushes the diaphragm in such a way as to move the valve disc more and
permitting more air to flow to secondary side and thus increasing the pressure again.
If the outlet pressure is high: whenever the less compressed air is consumed on secondary side
or load side, then load pressure increases. Therefore more force acts on diaphragm. The opposing
higher spring force pulls down the diaphragm in such a way as to move the valve disc less and
permitting air to flow to vent hole and thus decreasing the pressure again Non-Relieving or Non-Venting Type Pressure regulator
In this case compressed air cannot escape to the atmosphere in the event of high backpressure
acting on the diaphragm, as there is no exit path provided in the diaphragm for the trapped air.
Figure 1.5 shows the non –relieving venting type pressure regulator.
Figure 1.5 Non-venting type pressure regulators
Function: The function of air lubricator is to add a controlled amount of oil with air to ensure
proper lubrication of internal moving parts of pneumatic components. Lubricants are used to
 To reduce the wear of the moving parts
 Reduce the frictional losses
 Protect the equipment form corrosion
The lubricator adds the lubricating oil in the form of fine mist to reduce the friction and wear of
moving parts of pneumatic components such as valves, packing used in air actuators
Excessive lubrication is undesirable. Excessive lubrication may results in
 malfunctioning of components,
 seizing and sticking of components after prolonged downtime
 environmental pollution
Operation: The operation is similar to the principle of the carburettor. Schematic diagram is
shown in Figure 1.6. As air enters the lubricator its velocity is increased by a venture ring. The
pressure at the venture ring will be lower than the atmospheric pressure and the pressure on the
oil is atmospheric. Due to this pressure difference between the upper chamber and lower
chamber, oil will be drawn up in a riser tube. Oil droplets mix with the incoming air and form a
fine mist. The needle valve is used adjust the pressure differential between across the oil jet and
hence the oil flow rate. The air – oil mixture is forced to swirl as it leaves the central cylinder so
that large particles of oil is goes back to bowl and only the mist goes to outlet.
Figure 1.6 Air lubricator
The lubricator starts to operate only when there is sufficient flow of air. If too little air is drawn
off, the flow velocity at the nozzle is not sufficient to produce an adequate vacuum and hence to
draw oil out of the vessel. Only thin mineral oil may be used in pneumatic system lubricator.
Viscosity ratings are normally 10-50 Centistokes or SAE 10 . Table 1.2 give the normally used
oil. The list is purely alphabetic and not in order of preference.
Table 1.2 Typical oils used in air lubricator
Suitable oil grades/Trade name
Viscosity at 20
23.6 cSt
Avia Avilub RSL 3
34 cSt
BP Energol HL 40
27 cSt
ESSO SPINESSO 34, Nutto H5, H10
23 cSt
Mobil Vac HLP 9, Velocite oil no 6
25.3 cSt
Shell TELLUS OEL 15, OL 10
22 cSt
TEXACO Rando oil AAA
25 cSt
26 cSt
Vedol Andarin 38
20.5 cSt
Aral , Vitamol, GF10, DE10, CM5, CM10
21 cSt
1.1.4 Filter Regulator Lubricator Unit (FRL Unit) /Service Unit
Clean, dehydrated,
compressed air (97%)
with pressure variations
Clean, dehydrated,
compressed air
regulated at desired
pressure for spray
guns, food packing etc
Pressure vessel
with stored
compressed air
Emulsion made of
Lubricating oil &condensate
Polluted compressed
air, oil, water &
solid matter
Figure 1.7 Installation of FRL unit
Clean, dehydrated,
regulated, l ubricated
compressed air for
cylinders, valves, tools,
motors, etc
In most pneumatic systems, the compressed air is first filtered and then regulated to the specific
pressure and made to pass through a lubricator for lubricating the oil. Thus usually a filter,
regulator and lubricator are placed in the inlet line to each air circuit. They may be installed as
separate units, but more often they are used in the form of a combined unit. Figure 1.6 shows the
schematic arrangement of installation of Filter, Regulator and Lubricator unit .
The combination of filter, regulator and lubricator is called FRL unit or service unit. Figure 1.7
(a) gives the three dimensional view of FRL unit. Figure 1.7(b) gives detailed symbol of FRL
unit. Figure 1.7(c) gives simplified symbol of FRL unit.
Figure 1.7 a) Three dimensional view of FRL unit b) detained symbol c) simplified symbol of FRL
The main objective of air distribution system is to provide a distribution channel for compressed
air without any leak and keep the pressure drop within permissible limits. The air distribution
system consists of conductors and fittings which interconnect various components of a
pneumatic system. Figure 1.8 shows a typical air distribution system. It consists of compressor,
water cooled after cooler, Air receiver, dryer and ring main system. The air main takes the shape
of a ring. Air from main header is drawn by sub headers. Sub headers may have its own
Sub Header
outlet valve
Water cooler
Drop line
Quick connector
Discharge pipe
Air Receiver
Shut-off valve
Drain valve
Figure 1.8 : Typical Air distribution system ( Ring type)
The air distribution should take into account the following parameters
1. Choice of fluid conductor
2. Flow resistance
3. Correct sizing of pipes
4. Correct sizing of fittings.
5. Pipe layout
Objective Type Questions
1. Air filter, pressure regulator and lubricator are now built as packaged combination known as
FRL unit or ---------- units.
2. The pressure difference between inlet and outlet will indicate the degree to which the air filter
element is ---------3. In pneumatic system, pressure fluctuations occur due to variation in ---------- pressure or load
4. The main objective of air distribution system is to provide a distribution channel for
compressed air without any leak and keep the --------- within permissible limits.
5. Equivalent pipe length is length of straight pipe of the same -------- size giving the same
pressure drop
State True or False
1. Usually in line filter elements can remove contaminants in the 0.005-0.0005 micron range
2. A manifold type pneumatic network has the advantages that, being in the form of closed
circuit, the velocity of the air the main will be reduced and the pressure drop will be less.
3. Two Quality levels of air required in pneumatic production and distribution systems.
4. In Non-Venting Type Pressure regulator case compressed air cannot escape to the atmosphere
in the event of high backpressure acting on the diaphragm, as there is no exit path provided in
the diaphragm for the trapped air.
5. A single, large air compressor is more efficient and less costly than the several smaller units if
the demand is fairly constant
Review Questions
1. State the importance of fluid conditioning
2. Describe the function of air filter.
3. With help of neat sketch explain the working of air filter.
4. State clearly nine qualities of filtered air requirement and its application
5. Describe the function of an air pressure regulator
6. With the help of neat sketch explain the working of air regulator
7. Difference between venting and non-venting type of pressure regulator.
8. Describe the function of an air lubricator
9. With the help of neat sketch explain the working of air filter.
10. List commonly used oil in an air lubricator
11. State the advantage of main ring pneumatic net work
12. List five important considerations in pipe layout in pneumatic network
13. With the help of neat sketch, explain ring and manifold type of pneumatic network
14. List the guidelines for selection of pneumatic components and compressor
15. Discuss the three ways to remove the water from the air in the air distribution system
Fill in the Blanks
1. service
2. clogged
3. supply
4. pressure drop
5. diameter
State True or False
1. False
2. False
3. False
4. True
5. True
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