Prof.n.nagraj pneumatic control

PNEUMATIC CONTROLS
Contents
CHAPTER 1 Introduction to Pneumatic Controls
CHAPTER 2 Pneumatic Cylinders
CHAPTER 3 Direction Control Valves
CHAPTER 4 Controlling of Pneumatic Cylinders
CHAPTER 4A Speed Control of Cylinders
CHAPTER 5 Signal Processing in Pilot Operated Controls
CHAPTER 6 Pressure Dependent and Time Dependent Controls
CHAPTER 7 Co Ordinated Motion Control in Multi Cylinder
Applications
CHAPTER 8 Cascading Method of Signal Elimination in
Pneumatic Circuits
CHAPTER 9 Electro Pneumatics
CHAPTER 10 Compressed Air Production , Preparation and
Distribution

CHAPTER 1
INTRODUCTION TO PNEUMATIC CONTROL
The word ‘Pneuma’ means breath or air . Pneumatics is application of compressed air in
automation. In Pneumatic control, compressed air is used as the working medium,
normally at a pressure from 6 bar to 8 bar. Using Pneumatic Control, maximum force up
to 50 kN can be developed. Actuation of the controls can be manual, Pneumatic or
Electrical actuation. Signal medium such as compressed air at pressure of 1-2 bar can
be used [Pilot operated Pneumatics] or Electrical signals [ D.C or A.C source- 24V –
230V ] can be used [Electro pneumatics]
1.1 Characteristics of Compressed Air
The following characteristics of Compressed air speak for the application of Pneumatics
•Abundance of supply of air
•Transportation
•Storage
•Temperature
•Explosion Proof
•Cleanliness
•Speed
•Regulation
•Overload Proof
1.2 Selection Criteria for Pneumatic Control System
•Stroke
•Force
•Type of motion [Linear or Angular motion]
•Speed
•Size
•Service
•Sensitivity
•Safety and Reliability
•Energy Cost
•Controllability
•Handling
•Storage

1.3
Advantages of Pneumatic Control
•Unlimited Supply
•Storage
•Easily Transportable
•Clean
•Explosion Proof
•Controllable (Speed, Force)
•Overload Safe
•Speed of Working Elements
Disadvantages
•Cost
•Preparation
•Noise Pollution
•Limited Range of Force
(only economical up to 25 kN)
1.4 General Applications of Pneumatic Control
•Clamping
•Shifting
• Metering
•Orienting
•Feeding
•Ejection
•Braking
•Bonding
•Locking
•Packaging
•Feeding
•Door or Chute Control
•Transfer of Material
•Turning or Inverting of Parts
•Sorting of Parts
•Stacking of Components
•Stamping and Embossing of components
1.5 Applications in Manufacturing
•Drilling Operation
•Turning
•Milling
•Sawing
•Finishing

•Forming
•Quality Control
1.6 Structure of Pneumatic Control System
Figure 1.1 Structure of Pneumatic Control System
A typical Pneumatic control system comprises of the above groups of components. In
direct actuation controls signal processing group is not required. In electro pneumatic
Control signal processing can be carried out using combination of relays and contractors
or using PLC. The final control valves are solenoid actuated in the case of electro
pneumatic controls

CHAPTER 2
PNEUMATIC CYLINDERS
Drive Elements are Actuators – used to perform the task of exerting the required force at
the end of the stroke or used to create displacement by the movement of the piston.
Pneumatic Actuators can be classified as
•Single Acting Cylinders
Conventional Cylinder with Spring Loaded Piston or
Diaphragm type
•Double Acting Cylinders
2.1Symbolic Representation of Pneumatic Cylinders -Linear Actuators
Figure 2.1
2.2 Single Acting Cylinder
•Single acting cylinder has one working port
•Forward motion of the piston is accomplished to due to supply of compressed air behind
the piston.
•Return motion of piston takes place only due to built in reset spring placed on the rod
side of the cylinder.

•Single acting cylinders are used for applications such as clamping, feeding, sorting,
locking, ejecting, braking etc., where force is required to be exerted only in one direction..
•Single acting cylinder are usually available in short stroke lengths [ maximum length up
to 80 mm] due to the natural length of the spring.
Single Acting Cylinder exert force only in one direction.
Figure 2.2 Single Acting Cylinder
2.3 Double Acting Cylinders
They are available in different constructions such as
•Conventional,
•Double ended piston rod type,
•Rod less type
•Tandem type
•Multi-position type and
•Rotary type..
Conventional Cylinders
•Double Acting Cylinders are equipped with two working ports- one on the piston side
and the other on the rod side.
•To achieve forward motion of the cylinder, compressed air is admitted on the piston side
and the rod side is connected to exhaust. During return motion supply air admitted at the
rod side while the piston side volume is connected to the exhaust. Force is exerted by the
piston both during forward and return motion of cylinder
•Double acting cylinders are available in diameters from few mm to around 300 mm and
stroke lengths of few mm up to 2 meters

Figure 2.3 Double Acting Cylinder –Retracted and Advanced Positions
2.4 End Position Cushioning
•Pneumatic cylinders operates at much higher speeds than Hydraulic cylinders. Due to
this, there is a tendency of the piston to ram against the end covers as the piston
approaches the ends at high velocity especially in cylinder with large mass. This impact
force can damage the cylinder as well as the piston due to repetitive action .
•All Double acting cylinders excepting for small sizes, are provided with end position
cushioning arrangement.
•This arrangement decelerates the piston motion as it approaches the end of the stroke

Figure 2.4 Double Acting Cylinder with Cushions
2.5 Tandem Cylinder
•Tandem cylinder is essentially a combination of two cylinders in tandem such that force
derived from the first cylinder, supplements the force obtained by the second cylinder.
More or less the force produced by a tandem cylinder is as twice as that of a conventional
double acting cylinder of the same diameter.
•This type of cylinder is used where more force is to be generated and there is no scope
for increasing the diameter of cylinder due constraint of space
Figure 2.5 Tandem Cylinder
2.6 Rod less Cylinders
Different operational principals are used for the construction of Rod less cylinders:
1. Cable Cylinder
2. Sealing band Cylinder with slotted cylinder barrel
3. Cylinder with Magnetically Coupled Slide
Rod less cylinder have the following advantages:
•Available in long lengths –up to 4 m or even higher ( as there is no buckling)
•Most ideally suited for stopping and fixing (Robotic application)
•Occupies less space as the extension of piston rod is not present

2.6.1 Rod less Cylinder with Magnetic Coupling
This cylinder has a hermetically sealed arrangement where piston is housed inside a
sealed cylinder barrel. The piston is provided with number of annular ring magnets,
radially polarised. An external sleeve which slides over the cylinder, is also provided
with similar arrangement of ring magnets. Thus a magnetic coupling is established
between the piston and slider. As the piston reciprocates due to supply of compressed air,
the slider also reciprocates over the cylinder
Figure 2.10 Rod less cylinder with Magnetic coupling
2.6.2 Rod less Cylinder- Mechanically Coupled
The cylinder barrel is provided with a slot across the entire length. The force is
transmitted through a slide permanently connected to the piston. The connection from
piston to slide is directed outwards through the slotted cylinder barrel. The slot is sealed
by means of a sealing band, which seals the inside of the slot. The sealing band is guided
between the piston seals and passed under the slide. A second metallic cover strip,
covers the slot from the outside to prevent the ingress of dirt

Figure 2. 12 Rod less Cylinder Mechanical Coupled
2.7 Rotary Actuators
•In order to achieve angular motion, Rotary Actuators are used. Rotary actuators are
mainly available in two designs.
•Vane type Construction: Further these actuators are available with 1800
rotation or 2700
angle of rotation. These actuators can be used for low torque requirement up to 10 N-m.
•Rack and Pinion type construction: Can be used for angle or rotation close to 3600
.
These actuators can develop torques up to 100-150 N-m depending on the diameter of the
cylinder
2.7.1 Vane type Rotary Actuator
•A rotating vane connected to a shaft divides cylindrical chamber in to two compartments.
Compressed air is alternately admitted and exhausted from the chambers. The compressed
air pressure acting on the vane surface results in a torque. Hence rotary motion is obtained.
•The magnitude of the torque produced, depends on the surface area of the vane, air
pressure and mean radius of the vane.

Figure 2.13 Vane Type Rotary Actuator
2.7.2 Rotary Actuator of Rack and Pinion Type
This is essentially a double acting cylinder with a rack arrangement provided on the
piston rod and a pinion engages with this rack. Out put rotation of the pinion shaft can be
used for obtaining angular motion from 0-3600
. This type of rotary actuators are used for
higher torque requirement up to 150 N-m.

Figure 2.14 Rotary Actuator- Rack and Pinion Type
2.8 Cylinder Seals
•Cylinder seals of single cup or double cup type are often used for dynamic sealing
between piston and cylinder walls.
•Single cup seals are used for single acting cylinder and double cup seals are used in
Double acting cylinders
Figure 2.15 Single and Double Cup Seals
Sealing material such as Perbunan, Viton and Teflon are commonly used. Per bunan seals
are used for temperatures in the range of –200
C to 800
C while Viton seals are used for
high temperature range from –200
to 2000
C. Teflon seals have applications at low
temperature range –500
to 2000
C
2.9 Mounting Arrangement for cylinders

Figure 2.16 Mounting Arrangement of Cylinders
The type of mounting is determined by the manner of fitting the cylinder to fixtures and
machines. Flange mounting arrangement is generally used for small cylinders. Large
cylinders are usually foot mounted.
CHAPTER 3
Directional Control Valves
Directional Control valves are mainly used to change the direction of flow path of
working medium or signal medium. They are used for admitting or exhausting working
medium to the cylinder or from the cylinder for actuation of the cylinder. Also used to
start or stop the pneumatic signal as well as for signal processing

Directional control valves are designated as per the following functions:
•Number of ports on the valves
•Number of switching positions
•Method of actuation
•Method of reset
•Design and constructional features
3.1 Symbolic Representation of Directional Control Valves
Figure 3.1 Symbolic Representation of Directional Control Valves

Figure 3.2 Symbolic Representation of Directional Control Valve

Figure 3.3 Method of Actuation and Reset of Directional Control Valves

3.3 Energy Elements
Figure 3.4 Symbols for Energy Elements
3.4 Port Marking of Direction Control Valve
As per IS 1219 As per IS 5599
•
Supply Port A Supply Port 1
•Exhaust Ports R & S Exhaust Ports 3 & 5
•Out put Pots A & B Out put Ports 2 & 4
•Pilot Port [Set ] Z Pilot Port [Set] 14
•Pilot Port [Reset] Y Pilot Port [Reset] 12
3.6 Design and Construction Features of D.C. Valves
Directional Control Valves are available in the following types of constructions:
Poppet type of Valves
Ball Seat Type [Pneumatic/ Solenoid actuation]
Disc Seat Type [Pneumatic/ Solenoid actuation]
Slide Valves [Pneumatic/ Solenoid actuation]
Suspended Disc type of Valve [Pneumatic/ Solenoid actuation]
Plate of Valve [Manual actuation]

a. Selection Criteria of D.C. Valves
Selection of a particular design of D.C. valve depends on the following factors
•Actuation force
•Leak tightness
•Ease of servicing
•Sensitive to contamination by dirt
•Travel length of the valve stem
•Size
•Cost
3.8 3/2 Way- D.C. Valve N.C-Ball Seat Type
•These type of valves are often used as signal input valves, operated either with push
button or with limit switches rollers, to interrogate the cylinder position
•A spring loaded ball initially blocks the supply ports 1. Out put port 2 is connected to
exhaust port 3.
•On actuation, the plunger first isolates the exhaust port 3 and further descending of the
plunger, the ball is pushed down wards, there by opening the supply port 1 to out put
port 2.
Figure3. 5 Ball Seat Type Directional Control Valve [NC]

•These type of valves are often used as signal input valve either push button operation or
as limit switches to interrogate the cylinder position
•A spring loaded ball initially blocks the supply port 1 and out put port 2 is connected to
exhaust port 3.
•On actuation, the supply port 1 is connected to out put port 2. The exhaust port 3 is
isolated
3.9 3/2 Way Disc Seat Valve [Normally Closed]
Figure 3.6 3/2 Way Disc Seat Valve [Normally Closed]
Comparison of Ball Seat and Disc Seat Valves
Ball Seat Valves
•They are inexpensive
•Relatively small size
•Insensitive to dirt
•Operated manually or mechanically
Disc Seat Valve
•Offers large area and hence lift required is very small
•Time of response is good
•Insensitive to dirt
•Can be actuated manually, mechanically, electrically or pneumatically

3.11 5/2 Way Suspended Disc Seat Type of Valve
Figure 3.7 Suspended Disc Seat Directional Control Valve
These types of valves are widely used as it is insensitive to plugging by impurities,
require low actuation force. A manual over ride is shown on both sides to manually
set or reset the valves in case of signal locking. With pilot signal at pilot port 14, The
valve communicates ports 4 to 5 and 1 to 2. With pilot signal at pilot port 12., ports of
the valve 1 and 4 and 2 and 5 are communicated.. Used as final control element or for
signal processing.

Chapter 4
Controlling of Pneumatic Cylinders
Pneumatic cylinders can be controlled by the following methods:
1. Direct control of Single or Double acting cylinder
2. Indirect Control of Cylinder with Single Piloted Final Control Valve
3. Indirect Control of Cylinder with Double Piloted Final Control Valve
In the indirect control actuation, a pilot signal from a 3/2 N.C. valve is used to
activate pilot ports of final control valve.
4.1 Direct Control of Single Acting Cylinder
Figure 4.1 Direct Control of Single Acting Cylinder
Pneumatic cylinders can be directly actuated by actuation of final control valve, manually
or electrically in small cylinders as well as cylinders which operates at low speeds where
the flow rate requirements are less. When the directional control valve is actuated by
push button, the valve switches over to the open position, communicating working source
to the cylinder volume. This results in the forward motion of the piston. When the push
button is released, the reset spring of the valve restores the valve to the initial position
[closed]. The cylinder space is connected to exhaust port there by piston retracts either
due to spring or supply pressure applied from the other port.

4.2 Indirect Control of Single Acting Cylinder
Figure 4.2: Indirect Control of Single and Double Acting Cylinders
Large cylinders as well as cylinders operating at high speed are generally actuated
indirectly as the final control valve is required to handle large quantity of air. In the case
of pilot operated valves, a signal input valve [3/2 way N.C type, 1S1] either actuated
manually or mechanically is used to generate the pilot signal for the final control valve.
The signal pressure required can be around 1-1.5 bar. The working pressure passing
through the final control valve depends on the force requirement [4-6 bar]. Indirect
control as permits processing of input signals.
Single piloted valves are rarely used in applications where the piston has t o retract
immediately on taking out the set pilot signal -.suitable for large single acting cylinders.
4.3 Use Double Piloted Valve
Double piloted valve [Fig 3.3] is also called as the Memory valve
With the actuation of Forward push button, the out put signal activates the set pilot port
[14] of final control valve. This results forward motion of the cylinder
Now even if this push button is released the final control valve remains in the actuated
status as the both the pilot ports are exposed to the atmosphere pressure and the piston
remains in the forward end position.

Figure 4.3 Use of Double Piloted Valve
In order to retract the cylinder, the Return push button is activated. This will convey reset
signal from signal source to the pilot port of final control valve [12] . The piston retracts.
Now even if the Return push button is released the status of the cylinder will not change.
4.4 Methods of Checking The End Positions
The following methods are commonly used to interrogate the end positions of piston in
the cylinder:
1.Mechanically operated limit switches ( Roller lever or idle return roller type)
2. Reed sensors, either with electrical or pneumatic out put [the piston is incorporated
with ring magnet]
3. Electrical proximity switches
4. Pneumatic Signal generators
4.5 Use of Limit Switches
•S1 and S2 are the limit switches corresponding to home position and extended position
•Although they are located in the path of the movement of piston rod, normal practice is
to represent the symbol of the limit switches on either side of the final control valve
with out put signals connected to the pilot ports of the valve. The limit switches of Roller

lever type are essentially 3/2 way ball seat or disc seat type of valves handling pneumatic
signals. These are available with direct actuation type and internally pilot actuation type
versions. Limit switches of idle return roller type are used for actuation only in one
direction are used as signal elimination device in case of signal overlap.
Figure 4.4 Use of Mechanically operated Roller lever Limit Switches
Example 4.1 : Pin Feeding Device
Pins are to be fed from a hopper to the next station one at a time using a
Pneumatic Cylinder. Speed of the cylinder should be adjustable both during forward and
return motion. The process of feeding should be initiated using a detent push push
button. Develop a suitable Pneumatic control circuit .
F=0
S1 S2
2
1
S1
3
2
1
S2
3
4 2
1
14 12
5 3

Figure 4.7 Pin Feeding Device
F=0
S1 S2
2
1
S1
3
2
1
S2
3
75%
50%
4 2
1
14 12
5 3
2
1 3
Main Push button swithch
Figure 4.8 Pin Feeding Device
Exercise 4.1 : Rotary Indexing Table
Cans are required to be transferred from one conveyor to the other through a
filling and capping station. A rotary indexing device is used which should be able to
operate using a pneumatic cylinder with ratchet arrangement. The process should start on
actuation of a push button operated valve. The process should stop when no cans are
present from the incoming conveyor. The can sensor can be roller lever type of limit
switch . Draw a suitable pneumatic control circuit.

Figure 4.9 Rotary indexing device
CHAPTER 4A
SPEED CONTROL OF CYLINDERS
• It is always necessary to reduce the speed of cylinder from maximum speed based
on selected size of final control valve to the nominal speed depending on the
application
• Speed control of Pneumatic Cylinders can be conveniently achieved by
regulating the flow rate supply or exhaust air.
• The volume flow rate of air can be controlled by using flow control valves which
can be either Two way flow control valve or One way flow control valve
Flow Control Valves
• One way flow control valve is often used to achieve independent speed control of
cylinder in the forward and return motion. This has a variable restrictor and a non
return valve in parallel
• Two flow control valve is essentially a valve with variable restrictor which offers
resistance to passage of air in both direction.

Figure 4A.1 Symbol for Flow Control Valves
One Way Flow Control Valve
• This valve is also called as the Throttle Relief Valve
• Generally used for Speed Control of Cylinder and is installed in the working
pressure line, between the final control valve and the cylinder ports
• One way flow control valve has a needle and an orifice arrangement . A Non
return valve in the form of an elastic diaphragm is secured to the bottom of the
valve orifice. The diaphragm when subjected to air pressure from the top, seals
against seat in the valve body and prevents any direct air flow to the down stream
side. The compressed air has to necessarily pass through the flow control valve
and under goes throttling. When the flow takes place form bottom to top, the
diaphragm deflects upwards and allows air to pass directly to the down stream
side of the valve, thus by passing the flow control valve.
• When Compressed air is admitted in the direction of throttling, [left to right] it
exerts force above the diaphragm and holds it against the seat. This prevents by
passing of air through the gap between diaphragm and seat.
• Then compressed air has to pass through the gap between needle and orifice of
the valve which results in throttling

Figure 4A.2 One Way Flow Control Valve During Throttling
• When the flow takes place in the reverse direction, pressure exerted by the
compressed air from the bottom of the diaphragm, opens it up against the seat
and directly by passes the air without undergoing throttling
Figure 4A.3 One Way Flow Control Valve During Throttling

Figure 4A.4 Use of Flow Control Valve for Speed Control of Cylinder
Supply Air Throttling
Supply Air Throttling
• Supply air entering the cylinder through either of the working ports, undergoes
throttling as the non return valve is closed in the direction of flow.
• During exhaust , the compressed air leaving the cylinder is by passed through the
non return valve and escapes freely as it does not under go throttling
• Supply air throttling is used for single acting cylinder and small volume cylinder
Exhaust Air Throttling
• Supply air flows freely to the cylinder through the bypass passage of the non
return valve. The supply air does not under go any throttling
• Exhaust air leaving the cylinder has to under go throttling as the non return valve
is closed in the return direction
• The piston is loaded between two cushions of air
• Exhaust throttling should always be used for double acting cylinder
• Not suitable for small volume cylinders and cylinders with short strokes as
effective pressure cannot build up sufficiently.
Speed Control of cylinder

Figure 4A.5 Speed Control Valve
Stick Slip Effect
• There is a limitation is achieving smooth movement of cylinder with low speed
setting of flow control valve. This results in jerky motion of piston which is called
as the stick slip effect
• When the flow control valve is set for low flow rates, it takes considerable time
for the supply air to build up to the required pressure [corresponding to the load]
behind the piston. Every time this pressure is reached, the piston jerks in the
direction of motion which results in increase in cylinder volume. This further
results in drop in pressure in the cylinder and the piston momentarily halts until
the pressure build up takes place. This intermittent motion is called as the Stick
Slip Effect
Quick Exhaust Valve
• In many applications especially with single acting cylinders, it is a common
practice to increase the piston speed during retraction of the cylinder to save the
cycle time
• This is carried out by incorporating a Quick exhaust valve.
• The Quick exhaust valve has essentially three ports

Supply port 1, is connected to the out put of the final control element (Directional
control valve). The Output port, 2 of this valve is directly fitted on to the working
port of cylinder. The exhaust port, 3 is left open to the atmosphere
1
2
3
Figure 4A.6 Symbol for Quick Exhaust Valve
Forward Motion
During forward movement of piston, compressed air is directly admitted behind the
piston through ports 1 and 2 Port 3 is closed due to the supply pressure acting on the
diaphragm. Port 3 is usually provided with a silencer to minimise the noise due to
exhaust.
Figure 4A.7 Quick Exhaust Valve during Forward Motion

Return Motion
During return movement of piston, exhaust air from cylinder is directly exhausted to
atmosphere through opening 3 (usually larger and fitted with silencer) .Port 2 is
sealed by the diaphragm. Thus exhaust air is not required to pass through long and
narrow passages in the working line and final control valve
Figure 4A.8 Quick Exhaust Valve during Return Motion
Use of Quick Exhaust Valve

Figure 4A.9 Use of Quick Exhaust Valve
Example 4. 1
Liquid metal is drawn from a smelting crucible by a casting ladle and cast
in moulds. The raising and lowering of the ladle is controlled by separate manual
push buttons. The raising and lowering speed is separately adjustable . Design a
Pneumatic control circuit for this application

Figure 4A. 10 Casting Ladle Controlled by Cylinder
F=0
23%
50%
4 2
1
14 12
5 3
2
1 3
2
1 3
Figure 4A.11 Pneumatic Control for Casting Ladle
CHAPTER 5

SIGNAL PROCESSING DEVICES
To meet the requirement of various conditions in pneumatic applications, signal
processing devices are often used. The following gates or valves are used, depending on
the required conditions.
 OR Gate – Shuttle Valve – Used to select one of the two input
signals
 AND Gate- Two Pressure Valve- To combine two input signals i.e
to satisfy two conditions at the same time
 NOT Gate- 3/2 way, normally open, pilot operated Directional
Control Valve- Used to negate the function
Shuttle Valve
Figure 5.1 Shuttle Valve
• An Input Signal [1] can be applied on either side of the valve to obtain an out put
signal at port 2. A small aluminum or plastic ball or spool is used as the shuttle
which blocks the port opposite to the input signal.
OR Combination without Shuttle Valve

Figure 5.2 Circuit Diagram without Shuttle Valve
Use of Shuttle Valve

Figure 5.3 Circuit Diagram with Shuttle Valve
Figure 5.4 Circuit Diagram with Shuttle Valve (Actuated)

Two Pressure Valve
Figure 5.5 Two Pressure Valve
Input signal applied on any one side of the valve will block the signal passage on the
same side of the port. If a second signal is applied on the opposite side at the same
time, it will be communicated to the out put port.
And Gate Combination
2
1 3
2
1 3
2
1 3
2
1 3
2
1 3
2
1 3
1 1
2
1 1
2
S 1 S 2 S 3
S 1
S 2
S 3
Figure 5.6 and Gate Combination

Use of Two Pressure Valve
Use of Two Pressure Valve

Not Gate
2
1
10
3
Figure 5.9 Not Gate
Not Gate is generally used to invert the signal status i. e to negate the signal. For
example a normally closed timer or counter can be converted to normally open and
vice versa
It is essentially a normally open 3/2 way, pilot operated directional control valve
Input signal is applied at pilot port 10 and out put is taken from port 2.
Grouping of Set and Reset Signals
F=0
4 2
1
14 12
5 3
CONDITION 2 CONDITION 5
CONDITION 1
CONDITION 3
CONDITION 4
CONDITION 6
Figure 5.10 Grouping of Set and Reset Signals
Example 5.1 Clamping Device

The Clamping of workpiece must be possible slowly by manual control from two
positions.
Unclamping must be carried out quickly and initiated by a further manual push
button
Clamping must be possible only when the work pieces has been inserted
Unclamping must not be possible during the drilling operation.
Figure 5.11 Clamping Device

F=0
1 1
2
1 1
2
1 1
2
100%
1
2
3
4 2
1
14 12
5 3
2
1 3
2
1 3
2
1 3
2
1 3
2
1 3
CLAMP P.B CLAMP P.B.
UNCLAMP P.B.
DRILL SENSOR
WORK SENSOR
CLAMPING CYLINDER
Figure 5.12 Clamping Device –Control Circuit
Example 2: Distribution of Balls
Billiards balls are distributed from a gravity magazine via distributor shafts by two
packing stations for individual packing. The signal for the return stroke must be
capable of being given by the machine operator by means of either a manual push
button or a foot-operated valve. The advance stroke of the piston is triggered by the
piston rod when the rearmost end of position is reached.
The piston must execute a return stroke only when balls are present in the gravity
magazine.

Figure 5.13 Distributions of Balls
F=0
2
1
S1
3
2
1 3
4 2
1
14 12
5 3
1 1
2
1 1
2
100%
100%
PEDAL P.B.HAND P.B.
BALL SENSOR 2
1 3
S1
2
1 3
Figure 5.14 Distributions of Balls

Multi Position Cylinder
Normally we can get only two fixed positions [end positions] using a conventional
cylinder. However It is possible to attain 3 to 4 positions using combinations of two
cylinders of same or different lengths . The Cylinders are connected back to back using
appropriate size of flange mountings. Piston rod of one of the cylinder is trunion
mounted. This provides an economical solutions without going for elaborate electronic
control
Both the cylinders Retracted
Ist Cylinder advanced and IInd
Cylinder retracted
Ist Cylinder retracted and IInd
Cylinder is advanced
Both Cylinder Advanced
Figure 5.15 Multi position Cylinder Arrangement

Four positions can be obtained using combinations of two cylinders
Position Displacement Cylinder status
1 0 Both Cylinders retracted
2 L1 [Stroke length] Ist Cylinder advanced & II
Cylinder retracted
3 L2 [Stroke length I st Cylinder retracted & II
Cylinder advanced
4 L1+L2 Both the Cylinders advanced
4 2
1
14 12
5 3
1 1
2
1 1
2
1 1
2
1 1
2
2
1 3
2
1 3
2
1 3
2
1 3
F=0 F=0
S 1 S 2 S 3 S 4
Cylinder A
Cylinder B
4 2
1
14 12
5 3
Figure 5.16 Pneumatic Control Diagram

CHAPTER 6
PRESSURE AND TIME DEPENDENT VALVES
Pressure Dependent Valves
The following Pressure Dependent Controls are often used in Pneumatic applications
• Pressure Sequence Valve
• Pressure Relief Valve
• Pressure Regulator
Pressure Sequence Valves
Figure 6.1 Pressure Control Volves
• Pressure Sequence valve is essentially a switch on or off valve
• Sequence Valve generates a pneumatic signal if the sensing pressure [signal
input] is more than the desired set pressure
• This generated out put signal is used to control the movement of cylinder by using
it as a set signal or reset signal to the final control valve to obtain forward or
return motion respectively

• Used for applications such as bonding cylinders, clamping cylinder etc. to ensure
desired minimum pressure in the cylinder
• This is a combination valve, having two sections. One of the section is a 3/2
directional control and the other a pressure control valve
Pressure Sequence Valve
2
12 1
3
Figure 6.2 Pressure Sequence Valve
Sensing pressure signal is introduced at port 12
Manual adjustment of pressure setting is done with the help of a cap screw/knob
which is spring loaded. Clock wise rotation of knob results setting for higher pressure
setting and anticlockwise rotation of knob results in lower pressure setting.
The right section is basically a 3/2 directional control valve [NC] - pilot operated
using pressure signal derived from left section.
EMBED PBrush
Figure 6.3 Adjustable Pressure Sequence Valve

EMBED PBrush
Figure 6.4 Adjustable Pressure Sequence Valve. Actuated
Pressure Sequence Valve Circuit
Figure 6.5 Adjustable Sequence Valve Circuit

Pneumatic Timers
• Pneumatic Timers are used to create time delay of signals in pilot operated
circuits.
• Available as Normally Closed Timers and Normally Open Timers.
• Usually Pneumatic timers are On Delay Timers
Delay of signals is very commonly experienced in applications such as
• Bonding of two pieces.
• Normally Open Pneumatic Timer are also used in signal elimination
• Normally Open Pneumatic Timers are used as safety device in Two Hand
Blocks
Pneumatic Timers
ON DELAY TIMER NORMALLY OPEN AND NORMALLY CLOSED
Figure 6.6 Pneumatic Timers

Pneumatic Timers
100%
2
1
10
3
100%
2
1
12
3
NORMALLY CLOSED TIMER
NORMALLY OPEN TIMER
Figure 6.7 Pneumatic Timers
A Pneumatic Timer is a combination valve which consists of three parts
1. 3/2 way pilot operated directional control valve [NC or NO],
2. A one way flow control valve and
3. An accumulator
• Signal input is supplied at port 1 and delayed signal out put is taken at 2. A
signal source is connected at port 1
Time Delay Valve [N.C]

Figure 6.8 Details of Time Delay Valve [Normally Closed]
Application of Time Delay Valves
Figure 6.8 Time Delay Valve Circuit [N.C]

Ex.: 1 Use of Pressure Sequence Valve in Clamping Application
Work Pieces are to be clamped using a Pneumatic Cylinder. It is necessary that the
piston advances on actuation of a Hand Push button only after the desired pressure is
available in the working pressure supply. The piston should retract on releasing the
same push button
F=0
4 2
1
14 12
5 3
2
12 1
3
2
1
S1
3
2
1 3
1 1
2
S1
Figure 6.9 Use of Pressure Sequence Valve in Clamping Application
Exercise 2: Stamping of Badges
Badges are to be produced from a very thin metal sheet
A press with stamping die is available for this purpose . The double acting cylinder
should extend when both push buttons S1 and S2 are pressed simultaneously.
The return stroke to occur automatically only after preset pressure has been
reached in the cylinder at the forward end position[to get the consistent quality]
The cylinder should retract even if an Emergency push button S3 is pressed.

Figure 6.10 Stamping of Badges
Example 3: Clamping Device
Figure 6.9 Figure 6.9
Figure 6.11 Clamping Device

A push button is to control the forward stroke. After the piton rod has reached the
forward end position, the components are to be pressed together for 20 seconds. Then
the piston rod should return to initial position automatically.
The return stroke must occur even if the start push button is still depressed.
A new start signal may only become effective after the initial position has been
reached and after the push button has been released
Example 3: Clamping Device - Circuit
F=0
4 2
1
14 12
5 3
95%
2
1
10
3
50%
2
1
12
3
S1 S2
2
1
S2
3
2
1
S1
3
2
1 3
N.O Timer [ 2 sec} N.C. Timer [ 10 sec]
Figure 6.12 Clamping Devices – Circuit

Ex. 4: Two Hand Safety Block
A Pneumatic Cylinder has to advance on actuation of two push buttons
simultaneously [both the hands of the operator are engaged]. The second push button
is activated within short interval of time after actuation of first button.
/If any one of the push button is released, the piston of cylinder should Retract.
F=0
10%
2
1
10
3
1 1
2
1 1
2
2
1
10
3
2
1 3
2
1 3
4 2
1
14 12
5 3N.O.TIMER [2 Sec]
NOT GATE
P.B.2P.B. 1
Figure 6.13 Two Hand Safety Block
Exercise 2: Stamping Device
Articles are to be stamped using a stamping device
By pressing two push buttons simultaneously, the movable stamping die is pushed
down and the article is stamped .
After desired pressure is reached the die returns to its initial position even though the
push buttons are still pressed
Next cycle should be possible only after the push buttons are released

Figure 6.14 Stamping Device
Exercise 2: Bonding Application

Figure 6.15 Bonding Application
Plastic Cylinders are to be bonded using a Pneumatic cylinder.
It is required that piston performs forward stroke on actuation of a hand push button
Return motion should take place after the piston reaches forward end position
cylinder attains full pressure of 6 bar and remains in that position for 10 sec
It should be possible to restart the forward motion only 20 sec after the piston
reaches home position.
Development of Pneumatic Circuit

F=0
4 2
1
14 12
5 3
CONDITION 2 CONDITION 5
CONDITION 1
CONDITION 3
CONDITION 4
CONDITION 6
Figure 6.16 Development of Pneumatic Circuit
Bonding Application: Solution

F=0
4 2
1
14 12
5 3
2
12 1
3
100%
2
1
12
3100%
2
1
12
3
2
1
S1
3
2
1
S2
3
2
1 3
S1 S2
Text
N. C Timer [10 sec]
Pressure Sequence Valve[ 6 bar]
N.C. Timer [20 Sec]
Text
Figure 6.17 Bonding Application
CHAPTER 7

Coordinated Motion Control
In majority of the pneumatic applications more than one cylinder is used . The
movement of these cylinders are coordinated as per the required sequence
• The activation of limit switches of different cylinders will provide set or reset
signal to the final control valves for further controlling the movement of various
cylinders
• The limit switches have to be arranged in the proper location with the help of
motion diagram
Motion Diagram Step Displacement Diagram
Figure 6.1 Motion Diagram –Displacement Step Diagram
• In order to develop control circuitry for multi cylinder applications, it is necessary
to draw the motion diagram to understand the sequence of actuation of various
signal input switches-limit switches and sensors
• Motion diagram represents status of cylinder position -whether extended or
retracted
in a particular step
Example: Coordinated Motion Control for a Stamping Application

Figure 6.2: Clamping, Stamping and Ejection Application
Multi Cylinder Application with Two Cylinders A and B
Input Signals
• Cylinder A – Limit switch at home position ao
• Limit switch at home position a1
• Cylinder B - Limit switch at home position bo
• Limit switch at home position b1
Out put Signals
• Cylinder A advancing step is designated as A+
• Cylinder A retracting step is designated as A-
• Cylinder B advancing step is designated as B+
• Cylinder B retracting step is designated as B+
Designation of Signals

F=0
F=0
a 0 a 1
b 0 b 1
4 2
1
14 12
5 3
4 2
1
14 12
5 3
A + A - B + B -
Figure 6.3 Designation of Signals
Sequential Motion of Cylinders
It is possible to have the following sequence of operation
with two cylinders
Sequence Example of Application
A+, B+, A-,B- Lifting & Shifting / shifting of parts
in two directions ,
A+, B+. B-,A- Clamping & Stamping/Riveting
A+, A-, B+, B- Feeding and Ejection of parts
Example 1: Lifting and Shifting
• Products are required to be transferred from lower level conveyor to higher level
conveyor using two Pneumatic Cylinders
• Lifting Cylinder A lifts the product on receiving it at lower level
• Shifting Cylinder B shifts the product from the platform to the higher level
conveyor
• Lifting cylinder retracts
• Shifting cylinder retracts

Figure 6.4 : Schematic of Lifting and Shifting Application
Motion Diagram Lifting and Shifting
• Motion and Control Diagrams are shown for Lifting and Shifting Application:
A+,B+,A-,B-
• Signal 1.2 –Start Signal
• Signal 1.3- Extended position limit switch for cylinder B
• Signal 2.2- Extended position limit switch for cylinder A
• Signal 2.3-Home position limit switch for cylinder A
• NO SIGNAL OVER LAP

Figure 6.5 Control Diagram
Lifting and Shifting
F=0
4 2
1
14 12
5 3
2
1 3
2
1
B0
3
2
1
B1
3
F=0
4 2
1
14 12
5 3
2
1
A1
3
2
1
AO
3
AO A1 BO B1CYLINDER A CYLINDER B
START P.B.
Figure 6.6: Pneumatic Circuit Diagram for Lifting and Shifting

Signal Overlap
Signal Overlap can occur when simultaneously two active signals appear on both set
and reset pilot ports of Final Control Valve. This is due to the required sequencing of
cylinder. At the start, both signals ao and bo appear at the same time. This will not
result in any change.
4 2
1
14 12
5 3
2
1
B0
3
2
1
AO
3
6.7. Illustration of Signal over lap
Multi Cylinder Applications Signal Elimination
On analyzing the status of set signal and reset signal for final control valve for
different cylinders, it is observed that both set and reset signals could be present
simultaneously at any instant of time, depending on the sequential operation of the
cylinder. This does not permit further change in status of the valve. This situation is
termed as signal over lap. To overcome this problem signal elimination techniques are
used as listed below:
• Use of Idle return lever limit switches
• Use of N.O Timers
• Use of Cascading with the help of reversing valves
• Use of Stepper Sequencer modules
Example 2: Clamping and Riveting
• Sheet metal components are to be riveted using two Pneumatic Cylinders. A
Clamping cylinder (A) first advance and clamps the sheet metal parts.
• While the parts are clamped a second cylinder (B) advance and performs riveting
operation
• The riveting cylinder retracts and finally clamping cylinder retracts

Figure: 6.8 : Clamping and Riveting Using Pneumatic Cylinders
• Control Diagram is drawn below the motion diagram represents the status of
various signals- the limit switches used to interrogate the piston position
• Signals 1.4 and 1.3 correspond to home position and extended position limit
switches of cylinder A respectively
• Signals 2.2 and 2.3 correspond to home position and extended position limit
switches of cylinder B respectively

Figure 6..9 Control Diagram for Sequence A+,B+,B-, B-
Figure 6. 10 Pneumatic Control Circuit and Control Diagram

Figure 6.11 : Signal Over Lap at Step 3
Use of Idle Return Roller Limit Switch
2
1 3
2
1 3
ROLLER LEVER LIMIT SWITCH
IDLE RETURN ROLLER LIMIT SWITCH
Figure 6.12: Limit Switches
• Roller Lever type Limit Switch gives mechanical signal which can be sensed in
both direction movement of piston rod cam
• Idle Return Roller Limit Switch gives mechanical signal due to actuation of roller
only in one direction. This is conveniently used in Signal Elimination

Use of Idle Return Roller Limit Switches for Signal Elimination
Figure 6.13 Use of Idle Return Roller Limit Switch
Exercise for practice:
Develop Pneumatic control Circuit for Sequence of Operation A+,A-, B+,B-
Using Control Diagram to find out the signal overlap status.

CHAPTER 8
Cascading Method of Signal Elimination
Reversing Valves [Double piloted 5/2 way or 4/2 way] .These are signal processing
valves which are used to change over from one signal to next signal
Depending on the presence of set or reset signal at the reversing valves, output
change over takes place from port 4 to port 2 of the valve
There is no need to examine exact step where signal over lap occur in the circuit
Reversing Valves
When an input limit switch signal, S1 is generated , it is used to activate a Final
Control valve. This results in activation of a corresponding cylinder which is
followed by activation of a limit switch S2. This limit switch signal cancels the first
input signal S1 using a reversing valve and the same process continues
Conditions for Cascading
• Number of signal inputs [from limit switches] must be equal to number of output
signals [pilot signals to final control valves]
• Each input signal is assigned to a particular out put signal
• It should be possible to store an out put signal even when the corresponding input
signal is no longer present
• Only one out put signal may exist at any one point or it must be possible to
eliminate any specific output signal
• The input signal should be effective in the same required sequence
• No. of reversing valves required are (n-1), where n is total number signals from
limit switches or signal groups
Designation of Signals
F=0
F=0
a 0 a 1
b 0 b 1
4 2
1
14 12
5 3
4 2
1
14 12
5 3
A + A - B + B -
Figure 8.1. Designation of Signals From Limit Switches

Cascading Stages
4 2
1
14 12
5 3
4 2
1
14 12
5 3
I 1,I 2, and I 3 are Input Signals
I 1
I 2
I 3
SIGNAL LINES
O 1
O 2
O 3
O1,O2 and 03 are Out put Signals
Figure 8.2: Cascading Stages
Development of Cascade Stages
4 2
1
14 12
5 3
4 2
1
14 12
5 3
4 2
1
14 12
5 3
4 2
1
14 12
5 3
Reset Signal from Signal line S5
Reset signal from Signal line S3
Resest Signal from Signal line S2
I Input from Last signal + Start Switch
II Input from Limit Swtich e2
III rd Input from limit swtich e3
IV Input from Limit Switch e4
Last Input Signal from Limit Switch e5
Ist Out of Cascade to I Signal Line S1 II Out put of Cascade to Signal line S2
V Out put from cascade to Signal line S5
Out put from II Cascade to Signal line S3
IV Out put of Cascade to Signal line S4
Figure 8.3 Input Signals to Cascade Stages

2
1
A0
3
2
1
B0
3
2
1
A1
3
2
1
B1
3
4 2
1
14 12
5 3
4 2
1
14 12
5 3
4 2
1
14 12
5 3
2
1 3
Signal source
Start Push Button
Figure 8.4: Arrangement of Cascading Reversing Valves and Input Signals
Two Cylinder Co- Ordinated Motion Control [A+,B+,B-,A-]
• Sequence of operation
A+,B+,B-,A-
• Signal Groups
[ a1][b1][b0][a0]
• Last signal (a0) + Start signal is used to initiate the motion This will be input
signal to o last stage of cascade
Grouping of Signals
• Total number of cascade stages can further be reduced by grouping of signals.
• While grouping of signals, care should be taken not to include more than one
output signal from the same cylinder.
• Total number of cascade stages will be one less than number of signal groups.
Example 8.1 Clamping and Stamping ;Application
Required Sequence: A+,B+,B-,A-
Cylinder Sequence [ A+ , B+] [B-, A-]
Signal Sequence [ a1, b1 ] [bo, ao]
Signal Groups S1 S2

Circuit for Sequential Motion A+,B+,B-,A-,
F=0
4 2
1
14 12
5 3
4 2
1
14 12
5 3
2
1
A1
3
2
1
AO
3
2
1
BO
3
2
1
B1
3
AO A1
F=0
4 2
1
14 12
5 3
BO B1
2
1 3
Figure 8.5 : Circuit Diagram for Sequence A+,B+., B-, A+
Example 2
Required Sequence: A+,A-,B+,B-
Cylinder Sequence [ A+ ],[ A- ,B+], [B-]
Signal Sequence [ a1] , [ao ,b1],[ bo]
Signal Groups S1 S2 S3

Circuit for -Sequence Motion A+,A-,B+,B-
F=0
4 2
1
14 12
5 3
2
1
A1
3
2
1
B0
3
2
1 3
4 2
1
14 12
5 3
AO A1
F=0
4 2
1
14 12
5 3
B0 B1
2
1
AO
3
4 2
1
14 12
5 3
2
1
B1
3
START P.B.
Figure 8. 6 : Circuit Diagram for Sequence A+.A-, B+, B-

CHAPTER 10
Electro Pneumatics
Electro Pneumatic control integrates pneumatic and electrical technologies, is more
widely used for large applications. In Electro Pneumatics, the signal medium is the
electrical signal either AC or DC source is used. Working medium is compressed air.
Operating voltages from around 12 V to 220 Volts are often used. The final control valve
is activated [setting] by solenoid actuation
The resetting of the valve is either by spring [single Solenoid]or using another solenoid
[Double solenoid Valve] . More often the valve actuation/reset is achieved by pilot
assisted solenoid actuation to reduce the size and cost of the valve
Control of Electro Pneumatic system is carried out either using
combination of Relays and Contactors or with the help of Programmable
Logic Controllers [PLC]
A Relay is often is used to convert signal input from sensors and switches to number of
out put signals [ either normally closed or normally open] .
Signal processing can be easily achieved using relay and contactor combinations
A Programmable Logic Controller can be conveniently used to obtain the out puts as per
the required logic, time delay and sequential operation.. Finally the out put signals
are supplied to the solenoids activating the final control valves which controls the
movement of various cylinders. The greatest advantage of electro pneumatics is
the integration of various types of proximity sensors [electrical] and PLC for very
effective control. As the signal speed with electrical signal, can be much higher,
cycle time can be reduced and signal can be conveyed over long distances.
In Electro pneumatic controls, mainly three important steps are involved:
1. Signal input devices -Signal generation such as switches and contactor, Various
types of contact and proximity sensors
2. Signal Processing – Use of combination of Contactors of Relay or using
Programmable Logic Controllers
3. Signal Out puts – Out puts obtained after processing are used for activation of
solenoids, indicators or audible alarms

Symbols of Switches - Contactors
Figure 9.1 Symbols for Switches and contactors

Symbol- Single solenoid Valves
Single Solenoid Valve- Pilot assisted
Double Solenoid Valve- Pilot assisted
Figure 9.3 Symbolic Representation for Solenoids and Relays
Figure 9.4. Symbols of Solenoid Valves and Relays
4 2
1
5 3
2
1 3

Types of Relays
Figure 9.5 Types of Relays
Signal flow in Electro Pneumatic Circuit
Electro Pneumatic Control
Fig 9.6 Signal Flow in Pneumatic and Electrical Control Circuit

Control of Double Acting Cylinder
Indirect Action of Double Acting Cylinder Using a Relay
Figure 9.7 Control of Cylinder Movement indirectly using Relay
Indirect Actuation of Double Acting Cylinder for Forward and Return
Motion
Figure 9.8 Indirect Control of Double Acting Cylinder
F=0
4 2
1
Y1
5 3
+24V
0V
S1
Y1
K1
K1
1 2
2

With continuous Reciprocating Motion
Logic Circuits
OR Logic Circuit AND Logic Circuit
Figure 9.9: OR and AND Logic Circuit
Magnetic Reed Switches
Figure: 9.10 : Magnetic Reed Switches

•Magnetically operated Reed Switches consists of electrical contactors in a sealed glass
tube. The terminals of the contactors are taken out through an indicating lamp. The glass
tube is encapsulated in a housing filled with epoxy resin. It is necessary to have a
magnetic ring incorporated in the piston, so that when the piston is in the proximity of
reed switch ,the contactor will get closed and out put is available at the terminal
Electro Magnetic Relay
Relay is essentially a electromagnetic switch, operated at low voltage,
Relay has a relay coil and several contactors
Commonly 24V D.C source is used for relay coil and contactor circuit
Relay contactor out puts either NO or NC can be conveniently used for signal processing
Figure 9.11 Electro Magnetic relay with Symbol for multiple contactor
Holding Circuits
Dominant On Holding Circuit Dominant Off Holding Circuit
Dominant On circuit Dominant Off circuit

Figure 9.12 Holding Circuits
Pilot Assisted Solenoid Valve
Figure 9.13 Pilot Assisted solenoid Valve
Figure 9.14 3/2 Way Pilot Assisted Single Solenoid Valve [ Normally Closed]

Use of Proximate Sensor to Interrogate the End Positions of Piston
Figure 9.15 Example with Single Solenoid Valve Control
A Double acting cylinder is to be controlled using by a final control valve with single
solenoid and spring reset
•The piston is required to advance on actuation of a manual detent push button switch and
should continuously reciprocate from home to forward end position. The operation
should stop after release the detent push button.
•Holding circuit can be used for this purpose
Figure 9.16 Electro pneumatic circuit for Single Solenoid
F=0
4 2
1
Y1 Y2
5 3
+24V
0V
Y1 K2 Y2
S1 S2
K2
S1 S2
K1
Start Switch
Sensor 1
Sensor 2
1 2 3 4 5 6 7
7

CHAPTER 10
Compressed Air Production, Preparation and Distribution
Compressed air required for a Pneumatic Control System is produced and conditioned
using the following equipments which is termed as the Energy Elements:
•Air Compressor and Accessories
•Air Preparation
•Air Regulation
•Air Lubrication
Energy Elements
Figure 10.1 Symbol for Air Service Unit
Air Compressors
Air compressor used for generation of compressed air is selected on the basis of
desired delivery pressure and flow rate.
The following types of compressors are used depending the required flow rate of air and
maximum delivery pressure
 Piston type or Reciprocating Compressors
 Rotary type compressors- Vane type or Screw type
 Centrifugal type compressors
 Axial flow type compressor

Types of Air Compressors
Figure 10.2 Types of Air Compressors
Piston Type –Reciprocating Compressors

Figure 10.3: Reciprocating Compressor
Reciprocating Compressors are preferred for delivery pressure up to 8 bar with relatively
low flow rate. Single or Two stage compression with inter cooling between stages is
commonly used for air flow rate up to 20,000 cubic meters.
Diaphragm Type Compressor
Figure 10.4 Diaphragm Type Compressor
Compression takes place in the space separated by the diaphragm .The advantage of this
Compressors the totally oil free compressed air can be produced. Suitable for Food and
Pharmaceutical industries.
Screw Compressor
Figure 10.5 Screw Compressor
Screw compressor are used for moderate flow rates and moderate pressures up to 8 bar
and flow rates up to 15,000 cubic meters. It has greatest advantage of noise free operation
compared to piston type compressors as well as low energy consumption.

Vane Type of Compressor
Figure 10.6 Vane Type Rotary Compressor
It is a rotary compressor suitable for moderate pressure ratio and moderate flow rates
Centrifugal Compressor
Figure 10.7 Diaphragm Type Compressor

Centrifugal compressors are ideally suited for large flow rates and low pressure ratio of
around 4 per stage. Used only in large installation
Compressor Air System
Figure 10.8
The following accessories are used in a typical Air compression system
•Air Pre filter
•After Cooler
•Air Receiver
•Air Drying system: Adsorption type, Absorption type,Refrigeration type or using
semi permeable membranes
Commonly Adsorption Driers are for used for large air flow capacities and for dew point
up to –40 deg C

Air Receiver
Compressed Air Receiver is the most important accessory of air compression system
from the point of storage of energy, Horizontal or Vertical Receivers can be used
depending on available floor space. Air receivers should be equipped with delivery line,
Safety valve, Drain cock, Pressure gauge. Drain connection located at the bottom of the
Receiver is very important as the condensate collected in the Receiver should be
periodically drained either manually or automatically.
Compressed Air Filter
In compressed air filter, dust and moisture are arrested outside the filter element as the air
flows from out side to inside.
Available in various grades from 100 to 2 microns
Usually porous sintered bronze or ceramic filter elements are used.
Denser water particles which is collected on the outer surface of the filter element, gets
separated due to gravity and collects in the transparent bowl. This is periodically drained
with the help of manual drain cock. or automatic drain arrangement
Figure 10. 9 Compressed Air Filter
Maintenance of Filters
Care should be taken to see that the condensate level is always below the filter element so
that re entrapment of water in compressed air does not occur

Periodically the pressure drop across the filter should be monitored to check excessive
clogging of filter pores by dust. Some design of filters are provided with visual indicator
which indicates permissible contamination. When the indicator show red signal, it is
high time that the filter element is cleaned or replaced
Filter element is often cleaned with kerosene or soap water and compressed is air blown
in the opposite direction to purge out the dust clinging to the pores
Compressed Air Regulator
The Compressed Air Regulator serves two functions. The main function of the
compressed air pressure regulator is to maintain constant down stream pressure in the air
line, irrespective of variation of upstream pressure
In Vent type Regulators , if there is sudden surge or rise in pressure on the down stream
side of the Regulator [ may be due to sudden closure of valves], the equipment is safe
guarded from excess pressure by venting out the air through vent holes in the Pressure
Regulator
Construction of Regulator
The Pressure Regulator has a spring loaded metallic diaphragm provided with an aperture
A spring loaded plunger rests on the aperture. A valve disc is connected at the top
of the plunger, rests on valve seat, either opens or closes the air passage from
primary supply line to the down stream secondary line. The regulator body below
the diaphragm houses the main spring and an external knob to adjust the required
pressure setting . The body is provided with vent holes
Figure 10. 10 Compressed Air Regulator [Vent Type]
When the primary pressure on the upstream side of the Regulator is more than the
pressure setting of the Regulator, the pressure exerted by the primary pressure above the
diaphragm deflects it slightly downwards. This results in down ward movement of the

plunger. A valve disc at the top of the plunger closes the supply passage until the
pressure above the diaphragm falls below the spring setting of the regulator.
This result in deflection of the diaphragm upwards followed by upward movement of
plunger which further opens the supply line passage. The repeated movement of the
plunger and opening of closing of the valve disc results in an equilibrium setting for a
given pressure
During periods when the sudden closure of valves on the down stream side takes place
,the secondary line pressure is momentarily is more on the diaphragm thereby the
diaphragm deflects down wards The diaphragm deflects to a greater extent such that the
bottom of the plunger cannot close the aperture on the diaphragm there by relieving
excess pressure from secondary line to escape through aperture and vent holes
Figure 10.11. Compressed Air Service Unit
Compressor Air Lubricator

Figure 10.12. Compressed Air Lubricator
Lubrication of moving parts of cylinder and valves is very essential in Pneumatic system
For this purpose Compressed Air Lubricators are used ahead of each Pneumatic
equipment
Correct grade of lubricating oil usually with kinematic viscosity around 20- 50 centi-
stokes should be used.
Low pressure is created at the throat portion of the venturi due to flow of air taking place
in the Lubricator. This low pressure will assist automatic suction of the lubricating oil
from the oil bowl to the drip chamber where drop by drop of oil is diffused in to air
stream
Typical feature of any compressed air lubricator should incorporate the following:
•Automatic suction of oil from oil bowl due to suction created by the venturi portion
•Transparent Drip Chamber for visual observation
•Non return valve to prevent back flow of air from secondary to primary side of
lubricator
•Non return valve arrangement to prevent air loss during opening of oil bowl to replenish
the lubricating oil during operation without interruption
•Regulating screw for adjustment of oil feed rate in to air
•Transparent oil bowl with Oil filling cap
Operation
•Number of oil drops lets should be around 10 to 20 drops per 1000 lit of air .
•It is necessary to diffuse the lubricating oil in to compressed air in the form of fog or
mist
•The Lubricator should be preferably located not more than 5 m from the pneumatic
equipment
Compressed Air Distribution
Proper distribution of compressed air is very important to achieve good performance
.Some important requirements to be ensured are
•Piping Lay out [Open Figure 10.13 or Closed Loop Fig 10.14],Suitable number of drain
valves at diagonally opposite corners
•Piping Design [ Diameter of pipe for given flow, pressure drop, number and type of
fitting and absolute pressure-Using Nomograms]
•Slope of the main horizontal header from compressor [1:20]
•Take off branches from the top of horizontal headers with U or at 45 deg
•Provision of accumulator with drain cock at the bottom of all vertical headers
•Air service unit connected at right angles to vertical headers

Open Type Distribution System
Figure 10.13 Open Distribution System
This type of distribution can adopted for an existing buildings lay out. However the
terminal pressure keeps on reducing up to the last terminal due to pressure drop in the
piping.
Closed Loop Distribution System
Figure 10.14 Closed Loop Distribution

Pressure drop is uniform and as it closed loop, the terminal pressures are the same in all
the outlets. Proper planning of lay out the building is required for using this type of
distribution system.
References :
1. ‘Pneumatics Basic Level TP 101, by Peter Croser & Frank Ebel, Festo Didactic
Publication, -1999
2. Fundamental s of Pneumatic Control Engineering’ by J.P. Hasebrinki & R.
Kobbler, Festo Didactic Publications.
3. ‘ Fluid Sim P ‘ V3.6, Simulation Software Festo Didactic Product
Acknowledgement
I take this opportunity to convey my thanks to M/S Festo Controls Ltd, Bangalore for
kindly permitting me use their software ‘Fluid Sim P-V 3.6 [Didactic part] for my
presentations.

Prof.n.nagraj pneumatic control

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Prof.n.nagraj pneumatic control