14 Hydraulics and Pneumatics - Question Bank

IV Year- Mech.Engg. / ME 6021- Hydraulics and Pneumatics / Review Question & Answers

UNIT – 1

1. List out any four advantages of fluid power system?
 Multiplication of small forces to achieve greater forces for performing work.
 It easily provides infinite and stepless variable speed control.
 Accuracy in controlling small or large forces.
 Constant Forces/torque is possible in fluid power system.
 Simplicity, Safety & economy
 Greater efficiency (85-90%) due to low friction losses.
 Constant force and torque.

2. Why are hydraulic systems preferred for heavy work than the pneumatic systems?
Hydraulic system preferred for heavy work due to,
 High stability.
 Position accuracy is more. The precision is up to ±µm can be achieved.
 Protected against overload, with high system pressure of upto 600 bar.
 Energy cost is medium, whereas for pneumatic it is high.

2. Why are hydraulic systems preferred for heavy work than the pneumatic systems?
Hydraulic system preferred for heavy work due to,
 High stability.
 Position accuracy is more. The precision is up to ±µm can be achieved.
 Protected against overload, with high system pressure of upto 600 bar.
 Energy cost is medium, whereas for pneumatic it is high.

3. Where are pneumatic systems preferred?
 Pneumatic systems are preferred where low or medium size forces are required and
velocities are high.
 Because of their low cost, they are preferred in industrial automation.

4. Give any two differences between hydraulic power and pneumatic power.

Sl. No. Hydraulic power Pneumatic power

1 Power source is pressurized liquids such as Main power source is from

water, petroleum oils, compressed air, water compressed air.

glycols, water oil emulsion, silicones…, etc.

2 It is used for heavy load operation. It is suitable for medium load.

3 Operating pressure is upto 700 bars. Upto 17 bar

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5. Give the expression used to determine friction factor for laminar flow through pipes.
Friction factor for laminar flow
ƒ = 64/Re Re <2000
Re = Reynolds number

6. Name the different types of fluid power systems.
 Hydraulic power system.
 Pneumatic power system.

7. Give any four important properties of hydraulic fluids.

 Viscosity  Compressibility

 Viscosity index  Bulk modulus

 Flash and fire point  Cloud point

 Pour point  Oxidation stability

 Cavitation  Lubricity

8. State the effect of temperature and pressure on viscosity of gases.
 The viscosity of gases decreases with increase in temperature and vice versa.
 The viscosity of gases increases with increase in pressure.

9. Compare hydraulic and pneumatic drives for automation.

Sl. No. Pneumatic System Hydraulic system

1 Precise movement can’t be Precise movement can be

obtained due to compressibility. obtained.

2 High actuation speed. Less actuation speed.

3 Not required any special cooling Requires special cooling system.

system.

4 Unlimited design for automation. Limited design for automation.

5 More operation cycle. Less operation cycle.

10. State Pascal’s law with an industrial example.
It states that, “the pressure generated at any point on a confined fluid is transmitted
equally in all directions and acts at right angles to the containing surfaces”.
Example: Hand operated hydraulic jack, Hydraulic pressure booster.

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11. List out any four desirable properties of hydraulic fluids.

 Stable viscosity characteristics  Simple and easy handling
 Good lubricity  Low density and specific gravity
 Low volatility  Low coefficient of expansion
 Good oxidation stability  Compatibility with system materials.

12. Why fluid power system is called muscle of industry?
Fluid power is the technology that deals with the generation, control and transmission of
power using pressurized fluids. Now a day this technology is applied to most of the
industries. So, it can be said that fluid power is the muscles that moves industry.

13. Define the terms absolute viscosity and kinematic viscosity.
Absolute viscosity: It is defined by the force required to move a flat plate of unit area at
unit distance from a fixed plate with unit velocity when the space between the plates is
filled with a fluid whose viscosity is to be measured. Unit is N.S/m2.
Kinematic viscosity: It is defined as the absolute viscosity divided by mass density of the
oil. Unit is m2/sec.

14. Define fluid power
Fluid power means to convert, transmit, control, and apply fluid energy to perform some
useful work. Fluid power includes hydraulics and pneumatics.

15. Explain the term friction factor

 It is a factor used to calculate head loss due to calculate head loss due to friction in a pipe.

 According to Darcy’s equation , When, f= Friction Factor and HL= Head Loss.

 In case of Laminar flow ‘f’ is the function of Reynold’s Number only. i.e., .

 In case of Turbulent flow ‘f’ can be calculated using Moody’s diagram. i.e., using Re & Relative
Roughness .

16. List out the five fields of applications of fluid power?
Agriculture, Aviation, Fabrication industry, Machine tools, Oil industry and Pharmaceuticals.

17. What are the primary functions of hydraulic fluids?
 Transfer fluid power efficiently
 Lubricate the moving parts
 Absorb, carry and transfer the heat generated within the system

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18. What are the undesirable results when an oil viscosity is too high?

 The viscous oil may not be able to pass though the pipes

 The working temperature will increase because there will be internal friction

 The consumption of power will increase
19. What are the undesirable results when an oil viscosity is too low?

 The internal and external leakage will increase

 It cannot lubricate properly and will lead to rapid wear of the moving parts
20. What is viscosity index and give is its significance?

 The rate of change of viscosity with temperature is indicated on an arbitrary scale called
viscosity index (VI).

 The lower the viscosity index, the greater the variation in viscosity with changes in
temperature and vice versa.

21. What is Demulsibility?

The ability of a hydraulic fluid to separate rapidly from moisture and successfully

resist emulsification.

22. Define the term pour point and its importance?

 The temperature at which oil will congeal is referred to as the pour point, i.e. the lowest
temperature at which the oil is able to flow easily.

 It is of importance in cold countries where the system is exposed to very low
temperatures. The pour point must be well below the minimum temperature expected in

normal condition.

23. Name any four resistant fluids?

1.Water Glycols 2. Water oil Emulsion 3. Phosphate esters

24. What are the basic components that are required for a hydraulic system?

1.Reservoir 2.Pump 3. Prime mover 4. Valves 5. Actuator 6. Piping

25. List out the basic components of a pneumatic system?

1.Reservoir 2. Compressor 3. Prime mover 4. Valves 5. Actuator 6. Piping

26. What is the purpose of actuators?

Actuators are used to convert the fluid energy into mechanical force or torque to do useful

work.

27. Define the following terms with reference to hydraulic fluids?

1. Lubricity: It is the ability of a liquid to impart low friction under boundary conditions.

2. Compatibility: It is the ability of the hydraulic fluid to be compatible with the system.

3. Volatility: It is of a liquid describes the degree and rate at which it will vaporize under

given conditions of temperature and pressure.

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28. Define the term relative roughness?
The relative roughness is defined as the ratio between pipe inside surface roughness and the
inside diameter of the pipe.
29. What is a Moody diagram? Write its use?

 The Moody diagram contains many curves. The curves indicate the value of friction
factor as a function of Reynolds number and relative roughness.

 It can be used to determine the friction factor for use in Darcy’s equation.

UNIT-2

1. What are positive displacement pumps?
The positive displacement pumps discharge a fixed quantity of fluid into the hydraulic
system per revolution of pump shaft rotation.

2. What is non-positive displacement pump?
 If the pump ejects a variable amount of fluid into the hydraulic system per revolution
of pump shaft rotation, it is called non-positive displacement pump. It means that flow
rate of the pump per revolution is not constant.
 In non-positive displacement pumps, the fluid flow is achieved by using the inertia of
the fluid in motion. These pumps are typically used low pressure, high volume
applications
Applications: The non-positive displacement pumps are used only for transporting fluid
from one location to another location. They are not preferred in the fluid power industries
because these pumps cannot withstand high pressures.
Example: centrifugal pumps, axial pumps.

3. What is meant by variable displacement pump?
The displacement can be varied by changing the physical relationships of various pump
elements. This change in pump produces a change in output of fluid flow even though
pump speed remains constant.
Example: centrifugal pumps

4. Distinguish between positive and variable displacement pumps.

Sl. No. POSITIVE DISPLACEMENT VARIABLE DISPLACEMENT

1. The positive displacement pumps In variable displacement pumps, the

discharge fixed quantity of fluid into pump displacement can be varied by an

the hydraulic system per revolution arrangement.

of pump shaft rotation.

2. Ex. Gear pumps, Vane pumps Ex. Unbalanced Vane pump

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5. Where is rod less cylinders used?
Rodless cylinders were originally developed for use in all areas where space is restricted.
They provide a simple, compact and reliable method of transferring, moving or positioning
components or work pieces.

6. Why are double acting cylinders known as differential cylinders?
In double acting cylinders, areas on both sides of piston are different. Hence cylinder exert
greater force (low speed) when extending than during retraction. This results in different
pressure levels on either side of piston and that’s why they are called as differential
cylinders.

7. Mention few application’s where piston motors are employed?

The important applications of piston motors are

 Conveyor sorting  Positioning for welding

 Valve turning  Lifting

 Air bending operations  Rotating

 Flip over between work stations  Dumping

8. What is balanced vane pump?
In this pump, there are two inlet and outlet ports which are diametrically opposite to each
other. Because the pressure ports are opposite to each other, a complete hydraulic
balance is achieved.

9. Differentiate between balanced and unbalanced vane pump

Sl. No. Balanced vane pump Unbalanced vane pump

1. Cam ring is elliptical shape (in Cam ring is circular shape (in which the

which the rotor rotates). rotor rotates).

2. It cannot be used as a variable It can be used as a variable

displacement pump displacement pump

10. Draw the symbol of Bi-directional motor

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11. Give the symbols of pump

12. What are the advantages of rod less cylinders?  Quick and easy installation
 High precision and load capacity  Adjustable end stops
 Space-saving

13. A positive displacement pump has an overall efficiency of 73% and volumetric
efficiency of 79%. What is its mechanical efficiency?
Given: overall efficiency=73%; volumetric efficiency=79%
Formula: overall efficiency= volumetric efficiency x Mechanical efficiency

Mechanical efficiency x 100

Mechanical efficiency=(0.73/0.79) x 100
Mechanical efficiency=92.4%

14. When is lobe pump preferred?
When high volumetric displacement is needed, the lobe pump is preferred.

15. What is cylinder cushion?
Due to the inertia of forces of the moving parts at the end of piston travel, the piston will hit
the cylinder head at full speed. To overcome this, the designers provide an arrangement by
which the hydraulic cylinder can be slowly restarted or cushioned during the last portion
of the stroke. This is known as cylinder cushioning.

16. Why is end cushioning provided in hydraulic cylinder operations?
When the pressurized fluid enters in to the cylinder, the piston accelerates and travels
inside the cylinder. If the piston moves with the same speed inside the cylinder it will hit
the end cap with a great impact. To avoid this impact, the piston needs to decelerate at the
end of the travel. To achieve this cylinder cushioning is provided.

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17. Sketch the graphical symbol of
(a) Variable displacement reversible pump (b)Telescoping cylinder

18. What is pressure compensated flow control? How a variable vane pump can provide
this feature?
Pressure compensated flow control valve automatically adjusts to pressure changes and
maintains a constant pressure drop from inlet to outlet, thus providing constant flow.
By using cam ring and spring loaded compensator, the variable vane pump can provide this
feature.

19.Where the tandem types of cylinders are used?
 A tandem cylinder is one in which two or more piston rods are assembled as a rigid
unit. i.e., all pistons are mounted on single rod.
 There cylinders are used to obtain a low- force, high-speed action followed by a high-
force, low-action speed.

20. How to specify a pump?
 Operating speed
 Maximum discharge rate
 Maximum operating pressure
 Volumetric, mechanical and overall efficiency
 Overall dimensions.

21. What is a telescopic cylinder? What are its uses?
 A telescoping cylinder provides a relatively long working stroke for an overall reduced
length by employing several pistons which slides inside each other.
 These cylinders are useful for application requiring a long stroke but with only limited
space available for the unextended ram.

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22.Mention the significance of a telescopic cylinder with an industrial example?

Telescopic cylinder is used where there is a space constrains and it is also used to provide a
longer stroke.
Examples: hydraulic cranes, high-lift fork trucks
23. For the following graphical symbols shown, identify their modes of operation:

24. Identify the elements represented in the figure 1 and 2.

Figure 1 Figure 2

Figure1: Sequence Valve

Figure2: Solenoid operated spring return 4 way 2 position (4/2) direction control valve (DCV)

25.What is the function of pump in hydraulic system?
In a hydraulic system, a pump converts mechanical energy into hydraulic energy. Mechanical
energy is given to the pump via a prime mover such as an electric motor.
25. What is a positive displacement pump and how does it differ from a centrifugal
pump?

 Positive displacement pump is a pump in which there is a physical displacement of the
boundary of fluid mass.

 Centrifugal pump is a non positive displacement pump. In this there is a relative
motion between the fluid and rotor.

26. Why all gear pumps are fixed displacement pumps?
In gear pumps, the volumetric displacement depends on the design parameter of gears and
they cannot be varied. So the displacement cannot be varied.

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27. Name two designs of vane pumps?
a. Unbalanced Vane Pump b. Balanced Vane Pump

28. What are the advantages of balanced vane pump over the unbalanced vane pump?
 The balanced vane pumps eliminate the bearing side loads and thus permit higher
operating pressures.
 The balanced vane pumps have much improved service lives over simpler unbalanced
vane pump.

29. How can you vary the displacement in an axial piston pump?
 The variable displacement in an axial piston pump can be achieved by altering the
angle of the swash plate.
 Because in axial pumps, this swing angle determines the piston stroke and hence the
pump displacement.

30. Define the volumetric efficiency of the pump?
It indicates the amount of leakage within the pump. This involves considerations such as
manufacturing tolerances and flexing of the pump casing under the design pressure operating
conditions.

 v = Actual Flow rate producedby pump X 100
Theoretical flow rate the pump should produce

 v = QA
QT

31. Define the mechanical efficiency of a pump?
It indicates the amount of energy losses that occur due to reasons other than leakages. This
includes friction in bearings and between other mating parts. It also includes energy losses
due to fluid turbulence.

 m = Theoretical Power required to operate the pump x 100
Actual power delivered to the pump

 m = PQT
2NT

32. What are the types of hydraulic actuators?
 Hydraulic Cylinders – Linear motion
 Hydraulic Motors – Continuous rotary motion
 Semi rotary Actuators – Limited angle movement

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33. What is the purpose of hydraulic motor and how does it differ from the hydraulic
pump?

 The motor are actuated by the fluid. The fluid forces the motor to create the rotary
motion. The motor is mechanically linked to the load and develops torque. So a
hydraulic motor converts hydraulic energy into mechanical energy.

 But a pump converts the mechanical energy into hydraulic energy.

34. Name the construction types of hydraulic motors available?
 Gear type hydraulic motor
 Vane type hydraulic motor
 Piston type hydraulic motor

35. Where are external gear motors used?
External gear motors are used when relatively high speed and low torque is needed.

36. Define mechanical efficiency of a hydraulic motor?
η mech = Actual power given by the motor
Theoretical power it should deliver

37. What is a semi rotary actuator?
Semi rotary actuators convert pressure energy into torque, which turns through only limited
angle.
38. List few applications of semi rotary actuators?
Semi rotary actuators are used for lifting, tilting, opening, closing, indexing, swinging and
bending applications.
39. How is single acting cylinder retracted?
The single acting cylinder is retracted using gravity or by the inclusion of a compression
spring at the rod end of single acting cylinder.
40. What are the advantages of double acting cylinder over single acting cylinder?
 In a single acting cylinder, the fluid is fed only on one side. Hence the cylinder can produce

work in one direction only. But the fluid moves the piston in two directions in double
acting cylinder, so they perform work in both directions.
 In a single acting cylinder, the stroke is limited by the compressed length of the spring. But
the stroke in unlimited in a double acting cylinder.
 While the piston moves forward in a single acting cylinder, the fluid has to overcome the
pressure of the spring and hence some power is lost before the actual stroke of the piston
starts. But this problem is not present in a double acting cylinder.

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41. For what applications, a double rod cylinder is best suited?

The double rod cylinders are suitable when work has to be performed at either or both ends

and operating speed must be equal in both directions.

42. What is the advantage and disadvantage of tandem cylinder?

The tandem cylinder provides increased output force when the bore size of the cylinder is

limited. But the length of the cylinder is more than a standard cylinder and also requires a

larger flow rate to achieve a speed.

43. Name the different types of cylinder mountings?

1. Fixed centerline a. Tie rod end 3. Pivoted a.Rod end trunnion

mounts b. Rod end flange centerline mounts b.Blind end trunnion

c. Blind end flange c. Clevis

d. Centerline lugs d. Center trunnion

2. Fixed non a. End lug mounts

centerline mounts b. Side lug mounts

c. Integral key

mounts

d. Flush mounts

UNIT- 3

1. Draw the ANSI symbol for
i) A pilot – operated check valve and
ii) A shuttle valve

A pilot – operated check valve A shuttle valve

2. What are the functions of accumulators?

 The function of accumulator is to store the potential energy of an incompressible fluid
held under pressure by an external source against some dynamic force. (or)

 An accumulator is a device used to store the energy of liquid under pressure and make
this energy available as a quick secondary source of power to hydraulic machines.

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3. Draw the hydraulic symbols for a pressure –temperature compensated flow control
valve and Bidirectional motor

4. Draw the ANSI symbol for pressure relief valve

5. What is the function of shuttle valve?
What is the purpose of shuttle valve in pneumatic circuits?
 Shuttle valves control the direction of flow. Shuttle valves are used when control is
required from more than one power source. High pressure liquid comes out of the
outlet.
 The purpose of the shuttle valve is to select the higher of the two input pressures
automatically and connects to output port.

6. Differentiate pressure control and pressure relief valve
Pressure control valve controls the fluid pressure in a system whereas pressure relief valve
protects a system from excessive fluid pressure over the design pressure limit.

7. What is the purpose of synchronized hydraulic circuits?
To accomplish identical tasks from more than one cylinder at a same rate, synchronizing
circuits are employed.

8. What are the advantages of using intensifiers?
 Very high pressure can be supplied for shorter distance/time which eliminates the
use of very expensive, high pressure pumps.
 Low power input can be used to maintain a high pressure for a period of time.
 Automatically connects with the circuit when high pressure is required and
disconnects when demand is satisfied.

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9. What is an intensifier and where it is used?
A pressure intensifier is used to increase the pressure in a hydraulic system to a valve
above the pump discharge pressure. It accepts a high volume flow at relatively low pump
pressure and converts a portion of this flow to high pressure.

10. Highlight the need of using an intensifier in hydraulic circuits
List the applications of an intensifier.
 Intensifiers are used when; liquid of very high pressure is to be developed from
available low pressure.
 An intensifier is a device which converts low pressure fluid power into high pressure
fluid power. Intensifiers are used to multiply forces when a great force is needed for a
relatively short distance.

11. What is the function of solenoid valve?
A solenoid is an electromagnetic mechanical transducer that converts an electrical signal
into mechanical output force. It provides a push or pull force to remotely operate fluid
power lines.

12. Why are weight accumulators undesirable for mobile equipment’s?

Weight accumulators are undesirable for mobile equipment because of its large size and
heavy weight.

13. What is a bleed off circuit? What are its limitations?
The flow control valve controls flow to the cylinder by diverting an adjustable amount of pump’s
flow to the reservoir .Since the oil delivered to the cylinder does not have to flow through the flow
control valve; this circuit avoids dumping of excess oil through the relief valve. In the bleed off
circuit, the flow control valve is connected with its outlet port which is connected to the reservoir.

14. Define cracking pressure in pressure control valve
The pressure at which the relief valve begins to open is known as the cracking pressure.
(Extra: At this pressure, the poppet just begins to lift off its seat and some of the pump flow
begins to go through the relief valve back to the reservoir. The rest of the flow goes to the
system).
Note: The pressure at which the relief valve is completely open is known as the full-flow
pressure. The difference between the cracking pressure and the full-flow pressure is often
called as pressure override.

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15. What is the application of an unloading valve?
A type of pressure control valve located near a pump in order to depressurize (Unload) the
pump when a critical pressure (pre-set pressure) downstream has been reached.

16. Draw the hydraulic symbol for an unloading valve.

17. Draw a neat sketch of the graphical symbol for 3 position 4 way solenoid energized
pilot operated tandem centre direction control valve

18. List any four applications of accumulators.
 Leakage compensator
 Auxiliary power source
 Emergency power source
 Hydraulic shock absorber
 Thermal expansion compensator

19. What is meant by ladder diagram?
 A ladder diagram is representation of hardware connections between switches relays,
solenoids, etc. ., which constitute the basic components of an electrical Control system.
 In other words, a ladder diagram is nothing but an electrical diagram showing the
hardware connections between the various electrical control devices.

20. How sizing of accumulators is done?
In order to fully utilize the potential energy of the practically incompressible fluid and
compressed gas stored in the accumulator, the size of the accumulator must be done.

21. State the rule of thumb used in the sizing of reservoirs.
For weight – loaded type accumulators: Capacity = P x A x L
For gas- Loaded type accumulators: (i) P1V1 = P2 V2 = P3 V3
(ii)Size or total volume of the accumulator = volume of the compressed gas supplied +
Volume of the liquid required by the system

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22. What is the purpose of air pressure regulator?

The compressed air generated by the compressor will fluctuate. Changes in the pressure

level in the pipe system can adversely affect the switching characteristics of valves, the

running time of cylinders and the timing characteristics of flow control. The main purpose

of this valve is to regulate the incoming pressure of the system, so that the desired air

pressure is capable of flowing at a steady condition.

23. List any four basic types of electric switches used in electrically controlled fluid power

circuits

 Push-button switches  Temperature switches

 Limit switches  Relays

 Pressure switches  Timers

 Solenoids
24. Differentiate pressure switch and temperature switch.

 Pressure switches open or close contacts based on the system pressure.

 Temperature switches senses changes in temperature and open/close contacts when a
predetermined temperature is reached.

25. What are the three important things that are controlled in a hydraulic system?
In a hydraulic system, the pressure, direction and volume of flow are controlled. The pressure
is controlled to control the force. Flow is controlled to control the velocity. Direction is
controlled to obtain actuator motion in both directions.
26. What is the function of relief valve in a hydraulic system?
The function of a relief valve is to limit the system pressure to a specified maximum value by
diverting the pump flow back to the tank.
27. What are the advantages of compound relief valve over direct acting relief valve?
 Compound relief valves are usually smaller than the simple relief valves for the same flow

and pressure settings.
 They also have a wider range of maximum pressure setting.
 They can also be operated remotely by connecting a simple relief valve to the vent port.
28. What is the function of an unloading valve?
The unloading valve is useful to control the amount of flow at any given time in systems
having more than one fixed delivery pump.
29. What is the function of a sequence valve?
When the operation of two cylinders is required to be performed in sequence, the sequence
valve is used.

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30. When is the pressure reducing valve used in a hydraulic system?
Pressure reducing valve is used to maintain reduced pressure in specified locations of
hydraulic system.
31. Name one application of a counterbalance valve?
The counterbalance valve is used to maintain back pressure on a vertical cylinder to prevent it
from falling due to gravity.
32. What is a check valve?
The check valve is a one way valve, which allows flow in one direction on the other direction
the flow is not permitted.
33. How does a pilot operated check valve differ from a simple check valve?
Pilot operated check valve is a two way valve. This type of check valve allows free flow in one
direction. It allows flow in other direction also, when a pilot pressure is applied. But simple
check valve always allows flow in only one direction.
34. When are three way valves used in a hydraulic circuit?
Three way valves are used to operate single acting cylinders and two three way valves are
needed to operate a double acting cylinder.
35. What is meant by actuation of valve? List the various actuating devices of direction

control valves?
Actuation is a method of moving valve element from one position to another. The various
actuating devices are manually operated, mechanically operated, solenoid operated and pilot
operated.
36. What is meant when a flow control valve is said to be pressure compensated?
 The flow through the flow control valve varies as the square root of the pressure drop

across it. So any change in pressure at the outlet and inlet changes the flow through the
valve.
 Pressure compensated flow control adjusts automatically to pressure change and
maintains a constant pressure drop from inlet to outlet, thus provides constant flow.
37. What is the need for temperature compensation in flow control valves?
As the viscosity of oil varies with temperature, the oil becomes less viscous when temperature
increases. As the less viscous fluid flow more readily through an orifice, the increase in
temperature causes increase in flow for a valve setting. So temperature compensation is
needed to offset the effect of such temperature variations.
38. Name the three ways of applying flow control valves?

1. Meter in 2. Meter out 3. Bleed off

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39.Differentiate meter in and meter out control?

 In meter in type, the flow control valve is located in the pressure line leading to the
work cylinder. This type is used when load characteristics are constant and positive.

 In meter out type, the flow control valve is installed in the return side of the cylinder.
This type is used in machine tools like drills and mills in which the tool is dragged

suddenly.

40. What is a flow divider and name the different types?
Flow divider is a flow control valve and is used to divide the fluid from a single source into

two or more streams of equal flow.

1. Valve Type 2. Motor Type

41.What is the purpose of regenerative circuit and how is it attained?

A regenerative circuit is used to speedup the extending speed of a double acting cylinder. This

is attained by connecting the return flow from cylinder to pump flow.

42. Name the three basic types of accumulators used in hydraulic system?

a. Weight loaded type b. Spring loaded type c. Gas loaded type

43. What are the main criteria in the design of hydraulic system?

a. simplicity b. Reliability c. Efficiency d. Safety

e. Cost Effectiveness f. Maintainability

44. Which type of flow control valve is preferable if load on the actuator undergo

changes?

Pressure compensated flow control valve is selected, if load on the actuator undergo changes.

UNIT-4

1. Name any two pneumo hydraulic elements?
Compressor, Air tank, Prime mover, Control valves.

2. What are the advantages of fluidic control devices?
 They are not affected by severe vibration and shock.
 Simpler construction and easy maintenance.
 Relatively low cost.
 Highly reliable functionality.
 These devices are completely insensitive to radiation, even of extremely high levels.
Since air is normally used as the working fluid within these devices, there are no
problems of electrical noise, vibration, and fatigue and contact contamination.

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3. Distinguish between meter-in and meter –out circuits with respect to speed control
circuits?
 In meter-in-circuit, the flow control valve is located in the line leading to the inlet port
of the cylinder.
 In meter-out circuit, the flow control valve is located in the outlet line of the hydraulic
cylinder.

4. Give the flow control system employed in milling machine –table travel?
 Meter out flow control system is employed in milling machine.
 Reason: Mills passing through the workpiece often tend to drag the entire tool
forward (Tractive Loads). To avoid this, a back pressure is maintained in the exit
(exhaust) side of the actuator (meter-out) preventing the erratic motion.

5. State one method by which a quick return mechanism of a double acting cylinder
could be converted into equal speed operation?
By using Regenerative circuit the speed of extension is increased in order to get equal
speed of operation.

6. What is an FRL unit?
The combination of filter, regulator and lubricator is often labeled as FRL unit or service
unit.

7. What is the need for FRL unit?
What is the function FRL unit?
 The need of FRL unit is to remove contaminants, to regulate the incoming pressure, to
include drop of oil into the air stream.
 FILTER: the function of a filter is to remove contaminants from air before it reaches the
pneumatic components such as valves and actuators.
 REGULATOR: THE main function is to regulate the incoming pressure to the system, so
that the desired air pressure is capable of flowing at a steady condition
 LUBRICATOR: The function of the lubricator is to insert drop of oil into the air stream.

8. What is the need of air control valves in pneumatic systems?
 To start and stop pneumatic energy
 To control the directional flow of compressed air
 To control the flow rate of the compressed air
 To control the pressure rating of the compressed air

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9. Draw a circuit to automatically reciprocate a pneumatic cylinder using pressure
switch.

10. How do you rate a compressor?

 Outlet pressure of air that can be delivered by the compressor.

 Capacity or volume of the air that can be delivered.

 Compressor configuration and cylinder geometry.

11. What is the function of air filter and dryer?

 An air filter is to remove contaminants from the air before it reaches the pneumatic

components.

 The dryer is to reduce the relative humidity and dew point of the compressed air from

the compressor.

12. Name the various types of filters used in pneumatics

i. Suction line filter i. Woven wire cloth

ii. Pressure line filter ii. Paper filter

iii. Return line filter iii. Woven cloth media

iv. By pass and bleed off filter. iv. Sintered metal powder

(or) v. Ceramic and plastic media

13. How is the speed of cylinder controlled in pneumatic system?
With the help of air flow control valve, the actuation speed of cylinder is controlled.

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14. Sketch the graphical symbol of pneumatic regulator

15. Draw any one type of cylinder synchronizing circuit

16. Why are quick exhaust valves required?
A quick exhaust valve is a typical shuttle valve. The quick exhaust valve is used to exhaust
the cylinder air to atmosphere quickly. It is basically used with spring return single acting
pneumatic cylinders to increase the piston speed of cylinders.

17. What is a silencer?
It is a device that is used to control the noise caused by a rapidly exhausting air stream
flowing into the atmosphere.

18. List out the advantages of pneumo hydraulic circuit
State any four advantages of pneumatic hydraulic circuits
The pneumo hydraulic system use air and oil. By use of both media, the quick action of air
and smooth high pressure action of oil both can be achieved.

19. What is the purpose of fail-safe circuit?
The purpose of fail-safe circuit is to stop all the hydraulic action when an accident occurs to
the operator. For this, an emergency cut off valve is installed between the pump and the
master control valve.

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20. Quick exhaust valve is used to increase the piston speed of spring return single acting
pneumatic cylinder justify
The higher speed of piston in a cylinder is possible by reducing the resistance to flow of the
exhausting air during motion of cylinder. The resistance can be reduced by expelling the
exhausting air to atmosphere quickly by using quick exhaust valve.

21.What is the purpose of baffle plate in a fluid reservoir?
 The baffle plate is provided between the pump’s inlet and return lines for preventing the

continuous recirculation of the same fluid into the system.
 So the foreign particles from the returning fluid are allowed to settle down without any

disturbance and the trapped air is allowed to escape.
22.What are the main functions of a fluid reservoir?
 To provide a chamber in which any change in volume of the fluid in the hydraulic circuit

can be accommodated.
 To provide a radiating surface for allowing the fluid to cool.
 To provide a volume of fluid to allow entrapped air to separate and heavy contaminates to

settle.
23.When is pneumatics preferred over hydraulics?
Pneumatics is preferred over hydraulics when high speed and lower forces are required and
do not require high precision.
24.Name the three types of positive displacement compressors that are commonly used

in industry?
 Reciprocating piston type
 Rotary vane type
 Rotary screw type

25.What is a multistage compressor?
A compressor that draws in air and compress it to its final pressure in two or more stages is
called multistage compressor.
26.What is the need for mufflers?
 The use of exhausted air in industries has created noise problems. This air generates high

intensity sound energy, which causes fatigue to an operator.
 The muffler is used to reduce the energy of exhausted air, thereby reducing the noise.

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27.What is an F-R-L unit and give the graphic symbol of it?
F-R-L units is a combined unit of Filter-Regulator-Lubricator

28. Draw the graphic symbol and label the ports for a pneumatic?

29.State the difference between quick exhaust valve and flow control valve?
 The flow control valve is used to reduce the actuator speed from its normal speed.
 But quick exhaust valve accelerates the speed of the actuator.
30.Why air cylinders cannot be used for precise speed control?
Due to the compressibility characteristic of air, the air cylinder tends to slow down on
meeting increase in load and to accelerate when the load suddenly decreases. So air cylinders
cannot be employed for precise control.

31.Classify the pneumatic cylinders based on principle?

1. Single acting cylinder 2. Double acting cylinder

3. Tandem cylinder 4. Three position cylinder

5. Through rod cylinder 6. Adjustable stroke cylinder

7. Telescoping cylinder

32.Name the different types of air motors?

Piston Type – Axial, Radial

Vane type motor- Non reversible, Reversible

Turbine motor

33.Name the different hydro pneumatic appliances?

 Air oil reservoir

 Air oil cylinder

 Air oil intensifier

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UNIT-5

1. How servo systems are essential for fluid power circuits?
Servo systems provide:
 Signal amplification.
 Auto correction.

2. What are servo valves? Write their purpose in fluid power systems?
Servo valves are DC valves having infinitely variable positioning capability. They are used to
control not only the direction of flow but also the amount of flow.

3. State the 'Conda Effect' (Nov 2008-ME1305).
When a stream of fluid meets other stream, the effect is to change its direction of flow and
the effect is the fluid sticks to the wall. The Conda effect is also known as wall attachment
effect.

4. List the three types of proportional control valves
The three types of proportional control valves are:
 Proportional pressure relief valve
 Proportional pressure reducing valve
 Proportional direction control valve.

5. What is a bistable flip –flop?
A basic bistable flip-flop provides controlled assurance as to which of the two output ports
will deliver the power stream. The air flow will be from input stream Ps to either O1 output
port or O2 output port, depending on the existence of a signal from channel C1 or C2.

6. What is servo valve and how it is working?
A servo valve is a direction control valve which has infinite variable positioning capability.
Thus it can control not only the direction of fluid flow, but also the amount. Servo valves
are coupled with feedback sensing devices and thus a very accurate control of position,
velocity and acceleration of an actuator can be obtained.

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7. Where can fluidic devices be applied?

These devices are used where we need sensing, logic, memory, timing, and interfacing to

other control media.

8. How does a servo valve differ from proportional valve?

Sl. No. PROPORTIONAL VALVE SERVO VALVE

1. Use high power electronics Use low power electronics

2. Respond to control signals in the Require control signals in the range of

range of -10 to +10 volts. -100 to +100 mA.

3. Response time is 40-60 ms Response time is 5-10ms

4. Operating frequency is 10Hz Operating frequency is 100Hz.

9. State the role of microprocessor in fluid power industry

Microprocessor has a tremendous impact on industrial control and instrumentation due to

its high reliability and flexibility at the design and implementation stages. The decreasing

costs of microprocessor with increase in facilities in them are acting as catalyst in their

widening scope of application.

10. List the applications of PLC in fluid power control.
What is the use of PLC in fluid power control applications?

Programmable Logic Control (PLC) is one of the important microprocessor based

controller. PLC is being used in place of electromechanically relays or cam operated logic

controllers to control fluid power system.

11. List the components associated with PLC systems

 Central Processing Unit (CPU) with an associated memory

 Input modules

 Output modules

12. How do microprocessor differ from PLC’s?

Sl. No. Microprocessor PLC
1. A microprocessor is only one A PLC is a complete computer with a
component of an electronic microprocessor.
2. device.
Not built to operate under Designed for industrial environments
3. industrial conditions. where they can be exposed to heat,
4. humidity, corrosive atmosphere, etc.
All microprocessors are not All PLC’s contain one or more
used in PLC’s. microprocessors.
Do not accept analog data Accept analog data

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13. What is power pack?
What are the important components of a pneumatic power pack?
 They provide functions of pressure, direction and flow control within a basic pack.
 A power pack consists of a system of components like electric motor, pumps/compressor,
reservoir/receiver, shaft coupling, pressure gauges and safety valves to give pressurized fluid
for the fluid power system.

14. State any four common causes for hydraulic system breakdown
The common causes for hydraulic system breakdown are:
 Pump delivering insufficient oil.
 Pump making noise.
 Insufficient pressure in system

15. Excessive heating of oil in system. If an air cylinder produces erratic cylinder action,

identify the possible causes and also give the remedies for them?

Sl. No. CAUSES REMEDIES

1. Valve sticking or binding a) Check for dirt or gummy deposits
b) Check for worn parts

a) Check for over tightened packing on rod

2. Cylinder sticking or binding seal or piston.

b) Check for misalignment or worn parts.

16.What do you mean by logic control?

The logic control is a control based on logic functions like AND, OR, NOT etc. The components

of logic control are sensors and switching elements called binary elements. i.e. at any moment

they can be in one of the two states. ON-OFF.

17. Name the different pneumatic position sensors?

1. Pneumatic limit valves 2. Back Pressure sensor

3. Proximity sensor 4. Gap sensor

5. Limit switch

18. What are moving part logic elements (MPL)?

The MPL elements are miniature pneumatic elements. These elements are available as AND,

OR, NOT logic elements. The elements use moving parts such as diaphragms, spring, disks,

balls, poppets.

19. What is fluidics?

Fluidics is fluid logics. It is based on jet interaction. Fluidic elements have no mechanical

moving parts.

20. What are the advantages of fluidic elements?

 No wear and tear of elements

 No actuating force needed.

 Very little space needed for mounting

 Quite insensitive to temperature, vibration, shock, electric noise and radiation.

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21.Name the common methods used for designing logic circuits?
 Classic method
 Cascade method
 Step counter method
 KV map method
 Combinational circuit design

22.Draw the symbol for fluids OR element and write its truth table?

Truth Table

C1 C2 O1 O2

0 00 1

1 01 0

0 11 0

1 11 0

23. Draw the symbol for fluidic AND element and write its truth table?

Truth Table

C1 C2 O1 O2

0 00 1

1 00 1

0 10 1

11 10

24. What is the difference between pressure switch and a temperature switch?
Pressure switches open or close contacts based on the system pressure. Temperature
switches senses change in temperature and open or close contacts when a predetermined
temperature is reached.
25. How does a limit switch differ from a push button switch?
Push button switches are momentary switches. They make or break contact only as long as
they are held pressed. But limit switches make or break contact permanently when they are
actuated.
26. What is an electrical relay?
Electrical relay is a switch whose contacts open or close when its coil is energized. Relay are
used for energizing and de-energizing solenoids.

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27. What is a ladder diagram?
 The ladder diagram is a representation of hardware connection between switches, relays

and solenoids etc. Which constitute the basic components of an electrical control system.
 The left leg of the ladder connected to the power and the right to the ground.
28. What is the advantage of using microelectronic control for fluid power compared to
electro mechanical control?
 When the sequence changes, the hardwired electro mechanical has to be changed.
 This is expensive, but microelectronic control is programmable. So when the sequence

changes, the program only have to be changed.
29. What is a programmable logic controller PLC?
Programmable logic controller is defined as a digital electronic device that uses a
programmable memory to store instructions such as logic, sequencing, timing, counting and
arithmetic to control machine or processes.
30. What are the various approaches for entering the program in PLC?

 Ladder diagram based
 Low level language based on Boolean expressions
 Functional blocks
 High level languages
31. Explain why interfacing is necessary in a microprocessor control of fluid power?
Microprocessors usually work with different levels of voltages and currents than those used
by sensors and actuators. So an interface is needed to connect the items which are not directly
compatible.
32. What are the important requirements to get a maximum trouble free life from fluid
power system?
 Properly installed equipments
 Properly trained personnel
 Planned bolts preventive maintenance
 Effective troubleshooting
33. What is the meaning of the term “troubleshooting”?
The term troubleshooting means an organized and systematic study of the problem and a
logical approach to the difficulty faced in the system.
34.What is a servo valve and what is its function?
 Servo valve is a direction control valve which has infinite variable positioning capability.
Thus it can control not only the direction of fluid flow but also the amount.
 It gives a very accurate control of position and velocity of an actuator.

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PART – B:: QUESTIONS

UNIT – I

1. What are the basic components required for a hydraulic system? Explain their functions.

2. Explain hydraulic and pneumatic fluid power system.

3. Write the advantages and applications of fluid power in today’s life.

Describe any six advantages of fluid power systems.

Describe the advantages of fluid power systems

Discuss any four applications of fluid power.

List out the applications of fluid power employed in different industries/field?

4. What are various hydraulic fluids used in industrial hydraulic system?

5. Describe the general types of fluids used for fluid power system and its properties.

6. Compare and contrast between hydraulics, pneumatics and electro – mechanical power systems?

7. What are the advantages of hydraulics over pneumatics?

8. write briefly about the following hydraulic fluids

1) Petroleum oils 2) Emulsions 3) Glycols

9. Explain the advantages and limitations of using petroleum based hydraulic oils

10. List the precautions to be taken when a mineral oil based fluid is changed into fire resistant fluid.

11. Describe the properties of hydraulic fluids?

12. Explain in detail any eight desirable properties of a good hydraulic fluid.

13. Describe the general types of fluids used for fluid power system and its properties

What types of fluids are available in hydraulic systems? Explain two of them.

14. Fluid is flowing through a tapering pipe having diameters 50 mm and 25 mm at sections 1 and 2

respectively. The discharge through the pipe is 7.5 lps. The section 1 is 3m above the datum and

section 2 is 1.25 m above datum. If the pressure at section 1 is 200 KPa, find the pressure at section

2. The specific gravity of the fluid is 0.9?

15. Oil with specific gravity 0.9 enters as shown in fig.1 with velocity v1=5 m/s. The diameter at

section 1 is 10 cm ,the diameter at section 2 is 7 cm and diameter at section 3 is 6 cm .If equal flow

rates are to occur at sections 2 and 3 ,find v2 and v3 is m/s.

16. Fluid is flowing through a tapering pipe having diameters 50 mm and 25 mm at sections 1 and 2

respectively. The discharge through the pipe is 7.5Lps. The section 1 is 3 above datum and section

2 is 1.25 m above datum. If the pressure at section 1 is 200 KPa, find the pressure at section 2.The

specific gravity of the fluid is 0.9

17. Write Pascal’s law. Explain any one applications of Pascal’s law with neat diagram?

18. Differentiate laminar flows from Turbulent flows with examples

19. Write short notes on : 2. Reynolds number.
1. Laminar and turbulent flow

20. Derive Darcy's equation and how it is significant in hydraulics.

21. What is moody diagram and list the important characteristics of its.

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22. How to calculate friction losses in valves and fittings?
23. Hydraulic oil of kinematic viscosity 0.9 stokes, flows through a 35 mm diameter pipe at a velocity

of 4 m/s for a length of 100m. Find the head loss due to friction (in units of bar).Assume specific
gravity of oil as 0.9.
24. Explain Bernoulli's equation can be used to determine the pressure drop between two stations in
hydraulic system. Assume that there are some number of bends, tees, elbows, globe and gate
valves in between these two station separated by a long distance
25. Describe various losses in pipe, valves and fittings in hydraulic systems
How does one overcome the losses in pipes, valves and fittings in hydraulic power pack?
26. Fluid is flowing through a tapering pipe having diameters 50mm and 25mm at sections 1 and 2
respectively. The discharge through the pipe is 7.5Lps. The section 1 is 3m above the datum and
section 2 is 1.25m above datum. If the pressure at section 1 is 200KPa, find the pressure at section
2. The specific gravity of the fluid is 0.9?

UNIT-2

1. Explain how positive displacement pumps build pressure compared to rotor dynamic pumps.
What are the advantages of positive displacement pump?

2. Write short notes on variable displacement pump.
3. With a neat sketch, explain the construction and working principle of an external gear pump

Explain the working principle of external gear pump.
4. A gear pump has 75mm outside diameter, 50mm inside diameter and 25mm width. If the

volumetric efficiency is 95% at rated pressure what is the actual flow rate? N=1200 rpm.
5. A pump having a displacement of 80cm3, delivers oil at the rate of 1.25lps at 1200 rpm and 75bar.

If the prime mover input torque is 90Nm. Calculate the overall efficiency of the pump and the
theoretical torque required to operate the pump
6. Enumerate the working principles of balanced vane pump with neat sketch. Also write the
advantages and disadvantages?
7. Explain with neat diagram the construction and working of an unbalanced vane pump.
8. Explain the working of a gear type motor and vane type motors.
9. With a neat sketch explain the principle, construction, working, advantages, limitations and
applications of swash plate piston pump.
10. Explain the working of a radial piston pump with a neat sketch. Also write an expression for the
theoretical displacement per revolution of the crank?
11. Explain the working of a variable displacement pump axial piston pump with a neat sketch. Also
write an expression for the theoretical displacement per revolution of crank.
12. Find the offset angle for an axial piston pump that delivers 1.25 lps at 2000 rpm. The pump has
nine 12.7 mm diameter pistons arranged on a 130 mm diameter piston circle. The volumetric
efficiency is 94 %?
13. Explain the followings:

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i. pump characteristics curves

ii. pump cavitation

iii. pump noise

iv. Pump selection

14. What are the factors to be considered in selection for a pump?

15. List various types of hydraulic cylinders. Explain the construction, parts and working of double

acting cylinder with neat sketch

Explain the working principle of double acting cylinder with neat sketch.

16. Write short notes on telescopic cylinder and tandem cylinder.

Explain with neat sketch, the principle of operation of telescopic cylinder

17. Discuss any two types of cylinder mountings with neat sketch.

18. What is cylinder cushion? State its purpose.

Explain using a neat sketch "end cushioning" provide in hydraulic cylinders. Also sketch at least

six types of cylinder mounts available

19. What are fluid motors?

20. Define the terms used to evaluate the performance of hydraulic motors?

21. Discuss the working of piston motors with the help of a neat sketch

22. A hydraulic motor has a displacement of 150 cm³ and operates with a pressure of 85 bar and a

speed of 1800 rpm. If the actual flow rate consumed by the motor is 5 lps and the actual torque

delivered by the motor is 185N.m., find

a. Volumetric efficiency c. Overall efficiency, and

b. Mechanical efficiency d. KW power delivered by the motor.

23. A rotary vane air motor has a displacement volume of 80 cm³/rev and operates at 1750rpm

using 700 kPa gauge pressure air. Calculate the standard ml/min rate of consumption and kW

power output of the motor. Assume the temperature remains constant?

24. Determine the actual power required to drive a compressor that delivers air at 3.5 standard

m3/min at 8 gauge .The overall efficiency of the compressor is 74%.

25. What are the practical situations where in rotary actuators preferred over linear actuators?

26. If a hydraulic circuit has pump inlet and exit ports interchanged, unloading valve given internal

pilot .What happens? Explain.

UNIT-3

1. Discuss the construction and working of a solenoid actuated valve with a diagram.

2. Sketch neutral position for 3-position 4-way valves.

3. Explain the construction and working of the following components

 4/2 DCV  Sequence valve

 Shuttle valve  Flow control valve

4. What is the purpose of pressure compensated flow control valve?

5. Explain the construction and working of following control components

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 Check Valve
 Pressure reducing valve
6. Write short notes on shuttle valves.
7. Discuss the functioning of an unloading valve with a diagram.
8. Explain the working of a pilot operated pressure relief valve with neat sketch.
9. Explain the construction and working of pilot operated sequence valve
10. Distinguish between unloading valve and sequence valve.
11. What is counter balance valve? Explain with suitable circuit.
12. Write short notes on :
 Direct acting pressure reducing valve
 Pilot operated sequencing valve
13. Explain the working of hydraulic circuit used in drilling machine?
14. How 4/3 DCV is working in hydraulic power circuits? Explain the construction details with neat
sketch. Draw the graphical symbol of the valve?
15. Explain the different types of accumulator with neat sketch.
Explain with neat sketch weight loaded accumulator.
16. List the advantages and limitations of a spring loaded accumulator.
17. Define the use of accumulators in hydraulic circuits.
18. List out the different types of accumulators. Illustrate and explain any four applications of
accumulator used in hydraulic circuit
Make a circuit sketch, showing the use of an accumulator, as a hydraulic shock absorber
Explain with suitable circuit how an accumulator can be used as

 an emergency power source
 A leakage compensator.
Draw a circuit employing accumulator for supplying emergency hydraulic power.
19. Sketch any two circuits which employ hydro pneumatic accumulators for two different
applications. Also explain how the size of the accumulator is decided assuming the compression of
nitrogen in pneumatic accumulators to follow isothermal process?
20. Consider the charging and discharging of hydro pneumatic accumulator to be isothermal and
explain the procedure to arrive at the size of accumulator
21. An accumulator is loaded with 400KN weight. The ram has a diameter of 300 mm and stroke of
6m.Its friction may be taken has 5%. It takes 2min to fall through its full stroke. Find the total work
supplied and the power delivered to hydraulic appliances by the accumulator, when 0.0075 m³/s
of fluid is being delivered by a pump, while the accumulator descends with a stated velocity. Take
the density of oil is 1000N/m³.
22. A pump power pack is to supply the fluid flow demanded by a hydraulic system. The system
working pressure is 125 bar and the max pressure at accumulator is 200 bar. Assuming the
accumulator pre-charge pressure is 90% of its maximum working pressure, det.

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IV Year- Mech.Engg. / ME 6021- Hydraulics and Pneumatics / Review Question & Answers

 The actual pump delivery
 The max volume of fluid to be stored in accumulator
 The accumulator volume assuming an isothermal charge and discharge of accumulator
23. Give the applications of intensifiers and its symbol.
24. Explain air over oil intensifier. (Circuit)
25. Write and explain the working principle of pressure intensifier, with neat diagram
26. Draw and explain the basic hydraulic circuit employing an intensifier for using in a punching
press?
27. Draw and explain the ladder diagram connections for a regenerative circuit
28. Describe the hydraulic circuit for synchronizing two cylinders.
29. Develop a circuit involving two double acting cylinders A and B operating with the following
sequences: A+B+B-A- where + represents extension the rod and -represents retraction. Use only
sequence valves to obtain the sequencing.
30. Draw a single cylinder, continuous reciprocating cylinder using suitable components and also give
the specifications. (Single cylinder with limit switch)
31. Highlight the advantages of regenerative circuit and explain it with suitable applications.
32. Explain a hydraulic press circuit which employs double pump unloading principle.
33. Draw a closed hydrostatic transmission circuit and explain the functions of the components in it.
Also explain the function of replenishing circuit.
34. Describe the need of accumulators in hydraulic circuits and how sizing of accumulators are
provided.
35. Explain the commonly used electrical control devices in fluid power systems.
36. Explain various locations at which filters and strainers are filtered giving reasons

UNIT-4

1. Describe the function of air pressure regulator with neat sketch?

2. Using a neat sketch explain the construction and working of a pneumatic regulator. Also give its
graphical symbol.

3. Explain with its symbol and diagram functional filter, regulator and lubricator
4. With neat sketch, explain the importance of a filter and regulator unit in a pneumatic system .
5. With neat sketch explain the working of piston compressor.
6. Discuss the construction and function of a quick exhaust valve with a diagram
7. Explain with ANSI symbols

i. All the type of actuators used in pneumatics
ii. quick exhaust valve and silencer
8. Describe the functioning of air control valves?
9. Explain meter-in and meter-out circuits with neat sketch.
10. Describe the criteria for the choice between hydraulic and pneumatic circuits?

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IV Year- Mech.Engg. / ME 6021- Hydraulics and Pneumatics / Review Question & Answers

11. Design a car crushing system. The crushing force required is such that a 250 mm diameter cylinder
is required at a working pressure of 120kg/cm2.time for crushing is is about 10 s and the stroke
required to flatten the car is 300 cm. compare the power of the circuit with and without
accumulator.
i. Accumulator details:
ii. It is a gas loaded accumulator
iii. Time taken for charging =6 min
iv. Initial pressure of charging p1=100 kg/cm2
v. Charged pressure of accumulator p2 =225 kg/cm2
vi. Minimum pressure for crushing p3=120 kg/cm2.

12. Describe the various criteria for the selection of pneumatic components?
13. Classify the various types of pneumatic actuators?

A double acting pneumatic cylinder is required to provide the following operations: Fast extension

14.

till the mid stroke, slow extension till the end of stroke and on seizing the stroke end rapid return.
Develop a pneumatic circuit employing a shuttle valve and suitable flow control and other valves

15. Explain with a neat sketch of an air pilot control circuit for a double acting cylinder?
16. Explain with the neat sketch the working of semi –automatic control of double acting pneumatic

cylinder?
17. Make a circuit sketch for control of a double acting hydraulic cylinder
18. Design and draw speed control circuit for two cylinder operations. Also give the list of parts

required for the circuit.
19. Design and draw an electro hydraulic pneumatic circuit for the sequence A+B+B-A-. Also write a

ladder diagram. (Sequencing circuit; should not draw by cascade method)
20. Discuss in detail the considerations taken while designing a pneumatic circuit.
21. Draw a pneumatic circuit diagram and explain its working for cylinder cycle timing system.
22. Discuss with circuit diagram how the reciprocation of a cylinder is achieved by using pressure

switches in pneumatic circuits.
23. Discuss the procedure of the cascade method of designing sequencing circuits?
24. Design and draw a sequential circuit of a surface grinding machine using cascade method?

Design and draw a sequential circuit for shaping machine ram reciprocating using cascade method.
25. Develop an electro pneumatic circuit by cascade method for the following sequence A+,B+,B-,A-

where A and B stand for the cylinders , (+) indicates extension and (-) indicates retraction of the
cylinders ?
26. Valve bodies are to be marketed with the letters P, A, B and R. The valve bodies are placed in the
holder manually. Stamping cylinder A stamps the letter in the body and return cylinder B pushes
the parts from the holder into a basket and return to its initial position. Design a pneumatic
sequential circuit for the above operation using cascade.
27. Three pneumatic cylinders A, B, C are used in automatic sequence of operation. A cylinder extends,
C cylinder retracts, B cylinder retracts, and then A cylinder retracts, C cylinders extends and B
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IV Year- Mech.Engg. / ME 6021- Hydraulics and Pneumatics / Review Question & Answers

cylinder extends. Develop pneumatic circuits by cascade method. Also sketch travel step diagram.
28. What is displacement step or travel step diagram? Draw a displacement step diagram for cylinders

operating in sequence A+,B+,C+,C-,B-,A-,Write the cascaded pneumatic circuit for the above
problems.

Design and draw an electro hydraulic pneumatic circuit for the sequence A+B+C+C-B-A-.

UNIT-5

1. Explain the construction and working principle of hydro-mechanical servo valves with neat
diagram.
Explain the hydro mechanical servo valve with an industrial example.

2. Explain with a neat sketch construction and operation of a hydro mechanical servo system?
3. Explain the construction and working of a two stage electro hydraulic servo valve.

Draw a neat sketch of an electro hydraulic servo valve and indicate all components and give their
functions. Also develop the transfer function for the open loop gain for this valve.
4. Explain the electro hydraulic servo system with neat sketch.
What is electro hydraulic servo system? Write the advantages of the electro hydraulic servo
system over hydro mechanical servo system?
5. Draw and explain ladder diagram for electrical control of regenerative circuit.
6. What are proportional control valves? Write the types of proportional control valves?
7. Discuss the circuits for memory functions in fluidics.
8. Write short notes on bi stable flip flops.
9. How is AND function achieved in fluidic circuit?
10. Draw the block diagram of a PLC and explain the working of major elements?
11. What are PLC’s? Give their applications in low cost automation?
12. Explain the working principle of PLC with a neat sketch.
13. How the failure and trouble shooting is carried out in fluid power circuits?
How failure and trouble shooting is carried out in fluid power circuits?
14. List out the five types of faults that can be found in compressors. Also write the remedial actions
for the faults?
15. Give a detailed account of failure and trouble shooting of hydraulic and pneumatic power packs?
16. List out any four operational problems associated with pumps and valves and possible causes and
suitable remedy for each problem.
17. Discuss 8 common problems and its remedies in pneumatic circuits.
18. How does one overcome from the losses in pipes, valves and fittings in hydraulic power pack?
19. Discuss any one of the electro-hydraulic circuits used in robotic system?
20. What are the factors considered during the installation of pneumatic systems?
21. Explain the important factors in the maintenance of hydraulic and pneumatic systems in brief.

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