Pneumatics: Shuttle, Twin pressure, Quick Exhaust, Time Delay, FRL

1. Hydraulics & Pneumatics
Unit 5 : Pneumatics
Question & Answers
by
Abhishek D. Patange
Assistant Professor
College of Engineering Pune

2. Question 1:
• Explain construction and working of Shuttle valve
with schematic diagram used in pneumatics.
• Also explain electrical equivalent circuit, truth
table, Boolean expression, application for shuttle
valve as OR logic gate.
Answer is given on next page:

3. **Description is given on next page
Shuttle Valves (OR Gate)

4. Working:
A shuttle valve allows two alternate flow sources to be connected in a
one-branch circuit. The valve has two inlets P1 and P2 and one outlet A.
Outlet A receives flow from an inlet that is at a higher pressure. Figure
1.5 shows the operation of a shuttle valve. If the pressure at P1 is
greater than that at P2, the ball slides to the right and allows P1 to send
flow to outlet A. If the pressure at P2 is greater than that at P1, the ball
slides to the left and P2 supplies flow to outlet A .
Application:
One application for a shuttle valve is to have a primary pump inlet P1
and a secondary pump inlet P2 connected to the system outlet A The
secondary pump acts as a backup, supplying flow to the system if the
primary pump loses pressure. A shuttle valve is called an “OR” valve
because receiving a pressure input signal from either P1 or P2 causes a
pressure output signal to be sent to A
Shuttle Valves (OR Gate)

5. Shuttle valve as OR Gate
A+B
OR Electric Circuit OR Truth Table
Boolean expression
Application

6. Shuttle Valves application in circuit

7. Question 2:
• Explain construction and working of Twin
pressure/dual pressure valve with schematic
diagram used in pneumatics.
• Also explain electrical equivalent circuit, truth
table, Boolean expression, application for Twin
pressure/dual pressure valve as AND logic gate.
Answer is given on next page:

8. Twin pressure/dual pressure valve (AND Gate)
Valve body
Inlet 1 Inlet 2
Outlet
Reciprocating
spool

9. Working:
This valve is the pneumatic AND valve. It is also derivate of Non Return
Valve. A two pressure valve requires two pressurized inputs to allow an
output from itself. The cross sectional views of two pressure valve in two
positions are given in figure. As shown in the figure, this valve has two
inputs 1 and 2 and one output. If the compressed air is applied to either
1 or input 2, the spool moves to block the flow, and no signal appears at
output. If signals are applied to both the inputs 1 and 2, the compressed
air flows through the valve, and the signal appears at output.
Application:
These valve types are commonly associated but not limited to safety
circuits, for example a two push button operation system whereby an
operator is required to use both hands to activate two push buttons, this
would ensure the operators hands are out of reach of any hazardous
operations.
Twin pressure/dual pressure valve (AND Gate)

10. Twin pressure/dual pressure valve (AND Gate)

11. A*B
Twin pressure valve as AND Gate
AND Electric Circuit AND Truth Table
Boolean expression
Application

12. Twin pressure valve application in circuit

13. Question 3:
• Explain construction and working of time delay
valve with schematic diagram used in
pneumatics.
• Explain the application with circuit.
Answer is given on next page:

14. • It is used wherever delay of operation is required
Time delay valve

15. Time delay valve types

16. Time delay valve types

17. Time delay valve circuit animations

18. Circuit of time
delay valve
• In the circuit the
time delay
valve, holds the
cylinder in the
extended
position for the
pre determined
time, set on the
delay valve 1.4
1.21.4

19. Question 4:
• Explain construction and working of quick exhaust
valve with schematic diagram used in
pneumatics.
• Explain the application with circuit.
Answer is given on next page:

20. Quick Exhaust Valve
• These valves help mainly the DC valves to quickly
exhaust
• They are used for quick operation of actuators
Air enters from
main line to
cylinder
Air quickly exhausts to
atmosphere

21. A fast exhaust valve (Figure 4.26) is used to vent cylinders quickly. It is primarily
used with spring return (single- acting) pneumatic cylinders. The device shown in
Figure 4.26a consists of a movable disc which allows port A to be connected to
pressure port P or large exhaust port R. It acts like, and has the same symbol as,
a shuttle valve. A typical application is shown in Figure 4.26b.
Fast exhaust valves are usually mounted local to, or directly onto, cylinders and
speed up response by avoiding any delay from return pipes and control valves.
They also permit simpler control valves to be used.

22. A circuit using Quick Exhaust Valve

23. Question 6:
• Explain Speed control methods in pneumatics
and compare speed control in hydraulics and
pneumatics.
Answer is given on next page:

24. • 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.
• Meter In [throttling in]
• Meter Out [throttling out]
Speed control methods in pneumatics

25. 1V1: Meter In for controlling speed of extension
1V2: Meter In for controlling speed of retraction
2V1: Meter Out for controlling speed of retraction
2V2: Meter Out for controlling speed of extension
Speed control methods in pneumatics

26. Important: [Comparison of speed control in Hyd & Pne]
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.

27. Speed control methods in pneumatics animations

28. Question 6:
• Explain construction and working of FRL unit with
schematic diagram used in pneumatics. Draw
detailed symbol.
• Explain Filter with neat sketch.
• Explain Regulator with neat sketch.
• Explain Lubricator with neat sketch.
Answer is given on next page:

30. Filter construction

31. Filter working
• The construction of typical cartridge type filter along with graphical
symbols is shown in Figure.
• 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.
• 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.

32. Regulator construction

33. Regulator working
• A Relieving type pressure regulator is shown in Figure,
• 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.
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

34. Lubricator construction

35. • The operation is similar to the principle of the lubricator.
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.
• 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.
Lubricator working

36. Other important questions:
• Contamination control: Contamination, sources of
contamination [Unit 4]
• Small Numerical on strainer, filters, filter ratings. [Unit 4]
• FRL unit [Unit 5]
• Numerical on accumulators [Unit 2]
• Types of accumulators/symbols/working [Unit 2]
• Accumulator applications/functions/circuits [Unit 2]
• Typical Design numerical for 16 marks on [unit 6]