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947

HYDRAULICS AND PNEUMATICS

October 2019

PART – A

1. What is meant by fluid power?

Fluid power technology is means to convert, transmit, control and apply fluid energy

to perform useful work. Since a fluid can be either a liquid or a gas, fluid power in

general includes hydraulics and pneumatics. Oil hydraulics employs pressurized liquid

and pneumatics employs compressed air.

2. List out the types of piston pumps.

1. Axial piston pmps

2. Radial piston pmps

3. Duplex pumps

4. Triplex pumps

3. What is a spring return cylinder?

Spring return cylinder (or) single acting cylinder can exert a force only in the

extending direction, as fluid from the pump enters trough the blank end of the cylinder.

Single acting cylinders do not hydraulically retract. Retraction is accomplished by using

gravity or by the inclusion of a compression spring at the rod end.

4. What is the function of hydraulic ram?

Force multiplication is carried out the use of pascal’s law, it states that “The

pressure applied to be a confined fluid is transmitted undimished in all direction”

throughout the fluid and acts perpendicular to the surfaces in contact with the fluid.

5. What is the use of shuttle valve?

Shuttle valve allow alternative flow sources to be connected to a branch circuit.

They have two inlets and one outlet. Outlet permits to flow from whichever inlet is at a

higher pressure.

6. List out the types of heat exchangers.

1. Heat exchangers

A. Air cooled heat exchanger

B. Water cooled heat exchanger

B.1. Parallel flow heat exchanger

B.2. Counter flow heat exchanger

7. Mention the need for FRL unit.

It is the combination of filters regulator and lubricator units

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1. Filter

The main function of this valve is to regulate the incoming pressure to the system so

that the desired air pressure is capable of flowing at a steady condition

2. Regulator

The function of filter is to remove contaminants from air before it reached the

pneumatic components such as valves and actuators.

3. Lubricator

The function of the lubricator is to insert drops of oil into the air stream.

8. What is the function of hydraulic accumulator

A hydraulic accumulator is a device that stores the potential energy of an

incompressible fluid held under pressure by an external source against some dynamic

force. This dynamic force can come from three different sources.

1. Gravity

2. Mechanical

3. Compressed gases

The stored potential energy in the accumulators is a quick secondary source of

fluid power of doing useful work as required by the system.

PART – B

9. Define (i) Density (ii) Viscosity

Density – It is the ratio between mass of the fluids to volume. Nit is kg/ m3

Viscosity - viscosity of a liquid is designed as the resisting property of a liquid to its

flow. Unit is Newton sec/ meter2.

10. Write down advantages of vane pump

High performance sustained efficiency.

Self priming low shear

Speed up to 3600 rpm

Simple construction

11. List out various rotary actuators

a. Gear type

Internal gear type

External gear type

b. Vane type

c. Piston type

Axial type

Radial type

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12. What is a check valve? Draw the symbol

A valve permits single direction flow only is called check valve.

A ―< O― B

13. Mention the types of hydraulics seals

Hydraulic seals

a. Positive seals

b. Non positive seals

1. Static seals

a. Gaskets

b. ‘O’ rings

2. Dynamic seals

a. Contact seals

b. Lip type

c. Wipers

14. Differentiate between hydraulics and pneumatics

Sl.no Hydraulic Pneumatic

1. Resistant to fluctuating load Non-Resistant to fluctuating load

2. Speed is limited Very high speed is possible

3. Suitable for feed movement in

machine tools

Unsuitable for feed movement in

machine tools

4. Pump is necessary Need does not arise

5. Very precise stroke control

attainable Stroke control is easy

6. Operating pressure may be from

low to very high Operating pressure is generally 6 bar

7. Weight to pressure ratio is very

small Weight to pressure ratio is large

8. Cavitation is a big problem to be

tackled appropriately No such problem

9. System rigidity is good System rigidity is poor

10. Overall cost is moderate to high Overall cost is low

11. Moderate operating cost Very low operating cost

(Any 3 points)

15. What is the function of solenoid valve?

A solenoid is an electromechanical device which can convert electrical power in

to mechanical force. Solenoids provides a push (or) pull force to remolely operate fluid

power valves.

16. What is the purpose of telescopic cylinder?

Telescopic cylinders are used where long strokes are needed. A telescopic

cylinder provides a relatively long working stroke for an overall reduced long by

employing several pistons which telescope into each other.

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PART – C

17.(a) List the types of hydraulic pumps. Explain the working of external gear pump.

(Diagram = 5 mark

Explanation = 5 mark)

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17.(b) Explain the working of balanced vane pump.

(Diagram = 5 mark

Explanation = 5 mark)

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18.(a) Illustrate the use single acting cylinder with a circuit.

(Diagram = 5 mark

Explanation = 5 mark)

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18.(b) Explain the working of rack and pinion actuator.

(Diagram = 5 mark

Explanation = 5 mark)

19.(a) Explain the use of three way DCV with a sketch

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(Diagram = 5 mark

Explanation = 5 mark)

19.(b) Illustrate the working of needle valve

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(Diagram = 5 mark

Explanation = 5 mark)

20.(a) Explain meter – in speed control with a circuit diagram

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(Diagram = 5 mark

Explanation = 5 mark)

20.(b) Write brief notes on: (i) Temperature gauges (ii) Uses of intensifier circuits

A temperature gauge is a device used to indicate the temperature of an item being monitored.

The display can be analogue range or a digital readout.

Temperature gauges operate on the gas actuated, bimetal or expansion principle. They can be

measure temperatures between -200…+7000c. all instruments are also suitable for operation in thermo

wells.

Temperature gauges measure the thermal state of a homogenous substance. The measuring

system must be brought as closely together as possible with the body to be measure.. the most widely

used measuring methods rely on temperature – dependent physical and materials characteristics.

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Temperature Gauge

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(Diagram = 5 mark

Explanation = 5 mark)

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21.(a) Describe air preparation and distribution in pneumatics.

In pneumatic systems,compressors are used to compress and supply the necessary quantities of

air.compressors are typically of the piston,vane or screw type. Basically, a compressor increases the

pressure of a gas by reducing its volume as described by the perfect gas laws. Pnemuatic systems

normally use a large centralised air compressor, which is considered to be an infinte air source similar to

anizedair compressor. Which is considered to be an infinite air source similar to an electrical system

where we merely plug into an electrical outlet for electricity. In this way pressurized air can be piped

from one sourceto various locations throughout and entire indstrial plant. The compressed air pipe is

piped to each circiuit through an air filter to remove contaminants which might harm the closely fitting

parts of pneumatic compenents such as valves and cylinders. The air then flows through a pressure

regulator which reduces the pressure to the desired level for the particlar circuit applicatio. Because air

is not a good lubricant ( contains abot 20% oxygen) pneumatic system require a lubricator to inject a

very fine mist of oil into the air discharging from the pressure reglators. This prevents wear of the closely

fitting moving parts of pneumatic components.

In addition to using air dryers a distribution system can also be designed to keep water from the

machines. Three designed futures accomplish this:

1. Drop legs to the machines are taken upward, then down to the machine. This allows gravity

to prevent liquid water from reaching the machine.

2. Water drops legs with automatic drains are placed at various locations along the distribution

header. These are taken straight down off the header.

3. The distribution lines are sloped slightly downward (1/2 0 to 10 ) to keep any liquid water

that may be present moving along until it reaches a water drop leg.

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21.(b) Explain the working of two stage piston compressor.

(Diagram = 5 mark

Explanation = 5 mark

PREPARED BY

K.SARAVANAPERUMAL

DEPARTMENT OF ELECTRONICS(ROBOTICS)

LECTURER / ROBOTICS

222, APPC, PALANI