ME 2305 – APPLIED HYDRAULICS AND PNEUMATICS Two Marks Questions With Answers 2015

Anna University, Chennai




1. Define Fluid Power System. (Nov Dec 05) /(Nov/Dec11)

A system that transmits and controls power through use of a pressurized fluid within an

enclosed circuit.

2. Define Viscosity and bulk modulus of hydraulic fluid .(May June 06)

A measure of the internal friction or the resistance to fluid flow. actuator. Bulk modulus is the

measure of compressibility of a fluid .It is the reciprocal of compressibility.

3. Explain the term friction factor. (Nov Dec 06)

Friction factor is a dimensionless number required to calculate the energy losses due to

friction in the pipe. For laminar flow the friction factor f is function of Reynolds number only where as for turbulent flow f is a function of Reynolds number as well as the relative roughness of the pipe.

4. Name any four desirable characteristics of hydraulic pumps.(Apr May 05) (i)Pumps should provide safe and maximum system working pressure

(ii)They should have high volumetric and overall efficiency.

(iii) They should be compact and also have higher power to weight ratio. (iv) They should posses the variable displacement control

5. Name any four draw backs of Fluid Power System. (Apr May 05)

(i)Hydraulics fluid leakage poses many problems to the operation as well as operators.

(ii)Flammable hydraulic fluids may pose fire hazards thus limiting the upper level of working temperature.

(iii) Hydraulics elements require special treatments to protect them against rust, corrosion, dirt, etc., otherwise the contaminated elements may impair the system operation

6. How to classify direction control valves? (Nov Dec 05) (i) Two wave valves

(ii) Three wave valves

(iii) Four wave valves

7. Differentiate pressure compensated and non-pressure compensated pumps. (Nov/Dec11)

In pressure compensated pump, the pump flow can be made to zero. Such a pump has its own

protection against excessive pressure build up. Also there is no power waste and reduced fluid heating. Whereas non pressure compensated pumps are hydraulically unbalanced and cause undesirable side load on the bearings of the pump.

8. Write about positive displacement pumps? (Apr May 05) ( Nov Dec 12)

Positive displacement pumps have the internal working elements which make a very , close

fit together so that there is very little leakage (or) slippage between them. This type of pumps ejects a fixed quantity of liquid into the hydraulic system per revolution of the' pump shaft.

9. What is a sequencing circuit? (Nov Dec 06)

Process control pneumatics is also called as sequencing. It means performing number of

actions one after another which follows each other in a simple order or with an order determined by sensors.

10. What is pneumatic direction control valve? (Nov Dec 05)

Pneumatic direction control valve is used to control the direction of air path. These Valves

have generally two, three, four (or) five ports: These ports are designated as P: Compressor line port R: Exhaust port (T is case of hydraulics) A, B: Working ports connected to actuator.

11. Differentiate between oil hydraulics and pneumatics. (Nov Dec 10) (Nov Dec12)

i) Stability of the hydraulic system is high, since oil is almost incompressible and pressure level is considerably high. But the stability of the pneumatic system is low, since air is compressible.

ii)Energy cost of hydraulic system is medium. But Energy cost of the pneumatic system is


iii)In Hydraulic system, Controllable, high force. But in pneumatic system, Controllable, medium force.


1. What is the use of regenerative circuit? (Nov Dec 05) (NovDec12)

Regenerative circuit is used to increase the speed of extension stroke of the double acting hydraulic cylinder

2. What do you mean by non – positive displacement pump? (Nov Dec 06)

In non-positive displacement pumps, the fluid flow is achieved using the inertia of the fluid in

motion. Since these pumps cannot withstand high pressures, they are used only for transporting from one place to the another. For the same reason, they are not preferred in the fluid power


3. Why is the cylinder cushion? What is its purpose? (Nov Dec 06)

When the pressurized fluid is allowed to travel at the same speed till the end of stroke, 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. The arrangement made at the end caps to achieve the same is called cylinder


4. State the need for synchronization of hydraulic cylinders. (Apr May 05)

There are many industrial applications which require nearly perfect synchronization of

movement of two or more cylinders in order to complete some phase of operation.Synchronization is required where exact movement is required at both ends of a span,

such as on rolling equipment, power shears, power brakes, large presses, etc.

5. What is a hydraulic fuse?(Apr May 05)

A hydraulic fuse, analogous to an electric fuse, prevents hydraulic pressure from exceeding an

allowable value in order to protect circuit components from damage.

6. What is the difference between pilot operated and direct operated pressure relief valve?(May June 06)

Direct operated pressure relief valves are used where the flow rate and the system pressure are

reasonably smaller or there is not much variation in system pressure or flow rate. Whereas for a larger flow rate and higher pressure, pilot operated relief valves are used. The great advantages of pilot valve is that it can be kept spatially separated from the main valve.

7. What is meter-out circuit ?what are its applications? (Nov Dec 06)

In meter –out circuit ,the flow control valve is placed in the return line limiting the flow rate of

oil from cylinder. Even at no load ,the actuator is subjected to maximum pressure. Also as the cylinder is fed with the entire pump pressure ,pressure there is possibility of higher friction loss.

8. Define pressure override in pressure control valves. (Nov Dec 06)

The pressure at which the valves that opens is called the cracking pressure. The cracking and

closing pressure of the control valve is not same. Moreover in most cases ,the valve poppet

cracks at a pressure lower than the adjusted pressure but the valve closes at a lower pressure than at which it cracks.

9. Define FRL unit? (Nov Dec 05)/ (Nov/Dec11)

Air is not clean and hence contamination may result in pneumatic circuit. Also, due to time

fluctuations, the receiver air pressure does not remain constant. Also, some parts of the pneumatic system have to be lubricated for proper maintenance. For cleaning the air, regulating the pressure of air and lubricating pneumatic parts, three units 'Filter - Pressure Regulator - Lubricator' (Trio unit) are put together and this combined unit - Trio unit - is called FRL unit.

10. What is air receiver? (Apr May 06)

Air receiver is a large cylindrical vessel used to store high pressure air from the compressor. Large surface area of the receiver dissipates the heat of compression (heat in the compressed air) to the surrounding atmosphere. It will have safety relief valve, pressure indicator and

temperature switches.

11. Name four types of hydraulic cylinder mountings.

i) Rectangular flange mounting.

ii) Square flange Mounting. iii) Extended tie rod end.

iv) Double rod end.

12. Differentiate between single acting and double acting compressors. (Apr May 06)

In a single acting compressor, the compression takes place 011 one side of the piston for each

revolution of crank shaft. . In a double acting cylinder, compression takes place on both faces of the piston giving two compression strokes for each revolution of the crankshaft.


1. What is the function of accumulator? (Nov Dec 05)

Accumulator is used as an auxiliary power source. It is a device which stores the potential

energy of the fluid. The stored potential energy in the accumulator acts as a quick secondary source of power and does useful work as required by the system.

2. What are the most common applications of accumulators in hydraulic system?

1. Accumulator is used as an auxiliary power source 2.Accumulator is used as a compensator for an internal (or) external leakage. 3. Accumulator is used as an emergency power source4. Accumulator is used as a hydraulic shock absorber.

3. What are the functions of reservoir?(Apr May 05)

Reservoirs not only provide a storage facility for the liquid but can also serve to separate

entrained air, remove contaminants and dissipate heat from the liquid.

4. What is two way valves? (Apr May 05)

Two way valves contain two ports. Two way valves are generally used as check and shut- off


5. How do select hydraulic pipes for a hydraulic system? (Nov Dec 05) / Nov Dec


1.system pressure 2.pressure pulses 3.velocity of fluid flow 4.fluid compatibility 5.enviromental


6. What is meter-in circuit? what are its applications?( Nov Dec12)

In meter in circuit , the flow control valve is placed in the line leading to the inlet port of the

cylinder. There will be a drop in oil pressure fed to the cylinder due to throttling effect of the flow control valve. Hence for a low pressure, systems, meter in circuit is not preferred.

7. Distinguish between the pressure reducing valve and pressure relief by giving the graphical symbols. (May June 06)

pressure reducing valve maintains a prescribed reduced pressure at its outlet regardless of the

valve inlet pressure. But the pressure relief valve limits the maximum pressure that can be applied to the part of the system to which it is connected.

8. Differentiate between pressure control valve and pressure relief valve. (Nov Dec 06) Pressure control valve controls the fluid pressure in a system whereas pressure relief valve protects a system from excessive fluid pressure over and above the design pressure limit.

9. Write the functions of solenoid valve. (Nov Dec 06)

A solenoid is an electromagnetic mechanical transducer that converts an electrical signal into a mechanical output force. It provides a push or pull force to remotely operate fluid power valves.

10. State the role of PLC in fluid power industry. (Nov Dec 06)

PLC is designed as a replacement for hard-wired electro mechanical relays to control fluid

power systems.

11. What is PLC? (Apr May 05) (Nov Dec12)

PLC is a digital electronic device that uses a programmable memory to store instructions such

as logic, sequencing, timing counting and arithmetic to control machine or process.

12. Differentiate between single acting and double acting compressors. (Apr May 06)

In a single acting compressor, the compression takes place 011 one side of the piston for each

revolution of crank shaft. . In a double acting cylinder, compression takes place on both faces of

the piston giving two compression strokes for each revolution of the crankshaft.

13. How piston pumps are classified? (Nov Dec 06)

1. Radial piston pump 2. Piston pump with stationary cam and rotating block 3. Axial pump

with swash plate 4. Bent axis pump

14. What is an Electrical Relay? Nov Dec (2011)

Electric relay is a switch whose contacts open or close when its coil is energized. Relays are

used for energizing and de-energizing solenoids.

15. What is the purpose of an intensifier? What is gained and what is lost in an intensifier? Nov Dec (2011)

A hydraulic intensifier is a device which converts a large volume, low pressure fluid

supply in to a proportionately small- volume, high pressure fluid outlet.


1. What is ladder diagram? (Nov Dec 05) / Nov Dec (2011)

The ladder diagram is a representation of hardware connections between switches, relays,

solenoids, etc. The left leg of the ladder connected to the power and right to the ground.

2. What is the use of bleed-off circuit? (Apr May 05) ( Nov Dec12)

Bleed off circuit is used to .control the flow of fluid in both directions of flow (or) on a specific

line and limits speed in only one direction of the cylinder travel.

3. What is air-oil intensifier ? (Nov Dec 05)

Air over oil intensifier is used for driving a cylinder over a large at a low pressure and then over

a small distance at high pressure.

4. What is the need of lubricator unit in the pneumatic system? (Nov Dec 06)

The function of the lubricator unit is to add a controlled amount of oil with air to ensure proper

lubrication of internal moving parts of pneumatic components.

151. Name the various types of filters used in the pneumatic system? (Nov Dec 06)

1. Dry filter(with replaceable cartridges)

2. wet filter (where the incoming air is bubbled through an oil bath then passed through a wire mesh filter)

5. What is twin pressure valve? (Nov Dec 06)

Twin pressure valve, like counter balance valve, permits free flow in one direction and

restricted flow in the opposite direction.

6. What is meant by interlock contacts? (Apr May 06)

Interlock contacts are nothing but relay contacts. Relay are switches whose contacts open or

close when their corresponding coils are energized. The relay contacts provide interlock capability, which prevents the accidental energizing of two solenoids at the opposite ends of a valve spool. This safety feature can prevent the burn out of one or both of these solenoids.

7. What is Quick Exhaust Valve? Where are the these valves installed? (Nov Dec


If the flow rate in the system is constant, then the total energy in the system will also be

constant irrespective of the variation in the cross section of the fluid passages.

8. Explain non-separator type gas loaded accumulator? (Nov Dec 05)

In this type, the gas is filled at the top and the heavy oil at the bottom of the shell. There is no separator between the gas and oil and thus the pressurized gas pushes the oil directly.


1. What is a microprocessor?(May June 06)

A microprocessor is a multipurpose, programmable, clock driven, register – based

electronic device that reads binary instructions from a storage device called memory, accepts binary data as input and processes data according to those instructions, and

provides results as output.

2. Mention any two roles of pneumatic systems in low cost automation. (Apr May 05)

Pneumatic systems are popularly used for low cost automation (LCA)applications due to their

low cost ,ease of fabrication and safe operation.

3. What do you understand by single sequencing? (Apr May 05)

By sequencing a number of cylinders various machining and tooling operation may easily be

obtained in a machine .by using sequencing cylinders can be actuated one another in sequence like clamping ,unclamping and drilling.

4. What is power pack? (Nov Dec 05)

Power pack consists of a pump, electric motor ,reservoir and associated valving assembled to

one unit to supply pressurized fluid. They are relatively small in size and provide functions of pressure ,direction and flow control within the basic package.

5. How do microprocessor differ from PLCs? (Nov Dec 05)

1.PLCs are rugged and designed to withstand vibrations, temperature ,humidity and noise

2.The interfacing for inputs and outputs is inside the controller.

3.They are easily programmed and have an easily understood programming language.

6. What is servo valve? How does it work? (Nov Dec 06)

Servo valves are nothing but DC valves having infinitely variable positioning capability. A servo system is one in which the comparatively large amount of power is controlled by small impulses or command signals and any error are corrected by feedback signals.

7. Define condo effect. (Nov Dec 06)/ Nov Dec (2011)

When a stream of fluid meets other stream ,the effect is to change its direction of flow and

effect is the fluid sticks to the wall.

8. How do you rate a compressor ? (Nov Dec 06)

(i)outlet pressure of air that can be delivered by the compressor

(ii)capacity or volume of air that can be delivered by the compressor

(iii)compressor configuration and cylinder geometry

9. What are the important components of a hydraulic power pack? (Nov Dec 06) Hydraulic power pack consists of the pump ,drive motor, mechanical couplings, oil reservoir, strainers, filters, coolers, etc

10. What is Time delay circuit? (Nov Dec 05) (Nov Dec12)

In certain applications, the impulse to the main direction control valve may have to be delayed to pre-determined time for different operational reasons. A pneumatic time delay valve may be

used in such cases. A pneumatic circuit using this time delay valve is known as time delay circuit.

11. What is proportional valve? How it is different from a solenoid valve? Proportional valves, Similar to servo valves, use a variable force direct current solenoid to control the output from the main spool. Therefore the output is directly proportional to the input signal.

12. Define the term fluidics. Nov Dec (2011)

Fluidics is the technology that utilizes fluid flow phenomena in components and circuits to

perform a wide variety of control functions.