The whole pneumatic control system with P.I , P.D & P.I.D. explanation and equation.

1. Control Engineering
Pneumatic control system.
Prepared by : Rao Sai : 150050119541
: Mohamed Rajpurwala : 150050119540
Guided by : Nirmal sir

2. In pneumatic system the mechanical
power is converted to pneumatic power
by pressuring air or gas .
The major components of the pneumatic
system are :
• Compressor
• Receiver
• Filter lubricator regulator (FLR)
• Control valves
• Actuators
• Driers

4.  An air compressors as a device which is used to produce
compressed air .
 Air compressors are mainly of two types :
i. A reciprocating compressor which has a piston in a
sliding cylinder and the compressed air is delivered to a
server .
ii. A rotary compressors in which the impeller rotating at
very high speed in confined space so that the air is
compressed due to centrifugal action .

5. 1. Piston type reciprocating compressors :
 It consists of a piston which reciprocates in a cylinder and
it is driven by the connecting rod and crank.
 The inlet valve and delivery valve are mounted in the
cylinder head .These valves are automatically opened and
closed depending upon the pressure the valves between
outside and cylinder pressures .
 During the suction stroke , the inlet valve opens and air
enters the cylinder at atmospheric pressure.
 During the compression stroke the air is compressed at high
pressure . Now the delivery valve opens and the compressed
air from the cylinder is discharged to receiver at constant
pressure.

7.  In case the high discharge pressures of air are needed , then
two or three stage compressor are used .In order to reduce
the work of compression , the air after compression in low
pressure (LP) cylinder is cooled in an intercooler before
supplied to high pressure cylinder .
 Construction: These cylinders are radially mounted in V
shape .An intercooler is provided in between the cylinders to
reduce the work of compression . Other parts are similar to
the piston reciprocating air compressor .

8.  Working :The electric motor supplies the energy to drive the
compressor .When motor rotates it drives the crank of the LP
cylinder when the inlet valve opens it sucks the atmospheric
air through air filter .
 The compressed air is simultaneously cooled by transferring
the heat to cylinder .
 The compress air forces the delivery valve of the LP cylinder
to open and compressed air delivered to higher pressure
cylinder where it is further compressed and delivered
through its outlet valve to the receiver.
 In case the pressure in the receiver exceeds the set pressure
the safty valve automatically open and discharge the air to
atmosphere .

10.  Air coming out from the source and moving into the
pneumatic system needs to be supplied at constant pressure
irrespective of the source pressure
 Therefore , the regulators are pressure control valves which
are normally open type of valve .
 Function of pressure regulator :
• Air enters into the inlet of the regulator and depending on
the outlet pressure ,the valve stem will remain open to a
certain extent .

12.  Air entering into the pneumatic system is not
completely dry. It always contain a certain percentage
of lubricant to ensure that the moving parts operated
by the air are properly lubricated .

13. A pressure Vessel (Tank) normally made of metal and installed
either horizontally or vertically. This vessel provides a volume of air
to be utilized by the system and reduced the loading and unloading
of the compressor.
Air Receiver (Tank)

14.  Since the three components filter , regulator and lubricator
are essential components of any pneumatic system , and
combine all the three components into one unit called as FRL
unit .
 FRL units are installed at the beginning of the air supply line
so that air is filtered , regulated and lubricated prior to
entering the system .

17. • The force balance type controllers operate by converting
the controlled variable and set point in to corresponding
forces and manipulating these forces in order to produce
a pressure output.
• The advantage of this type of pneumatic controllers are
that greater flexibility is provided for achieving various
types of control actions.
• The set point is converted to a pressure and acts on one
side of a diaphragm is connected to the measured value
of the controlled variable converted to a proportional
pressure signal .The diaphragm will take the difference
between the two signals and create the error signal e.
• The conversion of both the set point as well as measured
value to pressure signals is achieved by flapper nozzles.

21.  It is same as proportional controller .

22.  WORKING :
 When there is an increase in the error signale , like a step change ,
the flapper moves close to the nozzle which increses the back
pressure m.
 The back pressure is fed back through the propotinal bellow as
negative feedback.
 Due to the increase in back pressure , there is an increased presuure
drop across the needle valve. So there is a gradual flow of air into
the positive feedback bellow.

24.  This control can be obtain by adding a feedback restriction in the
feedback restriction in the feedback path.

25.  Working :
 Let the input error signal be changing linearly with time.the flapper
will move slowly towards the nozzle. the back pressure will slowly
increse due to this .
 Due to this increase in the back pressure feedback bellow will slowly
start increasing. This is because air takes time to leak through the
restriction.
 Thus the feedback is delayed and lags the input.

27.  It has the basic component same as the in propotional control . That
is flapper nozzle system . Input is given to the flpper and output is
the back pressure.

28.  WORKING :
 Derivative action is produced by providing a restriction in the
negative feedback path of the derivative bellow. the needle valve can
be used to adjust the derivative time.
 Integral action is produced as earlier by providing positive feedback
through a restriction using a needle valve to the integral bellow.
 Thus the combination provides all the three modes of control.

30. Thank You.