Hydraulic Components | Interview Question and Answers

Hydraulic Components – Hydraulic and Pneumatic| Interview, viva ,oral Question and Answers

1. Name the basic components required in hydraulic system.

(i) Pump (ii) Hydraulic valves (iii)Hydraulic actuators.

2. 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.
• In positive displacement pump, the outlet flow is independent of system pressure. But in centrifugal pump the outlet flow is dependent on system pressure. So when pressure increases, the flow reduces.

3. What is the function of pump in a 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.

4. Name the three popular construction types of positive displacement pumps.

(i) Gear pumps (ii) Vane pumps (iii) Piston pumps.

5. Name the different designs of gear pump.

(i) External gear pump (ii) Internal gear pump (iii) Lobe pump (iv) Screw pump.

6. Why is the operation of a screw pump quiet?

In the screw pump, the fluid does not rotate but moves linearly. Thus even at higher speed, there are no pulsations. So it is a quiet operating pump.

7. Name the different designs of vane pump.

(i) Unbalanced vane pump (ii) Balanced vane pump.

8. What is the difference between fixed displacement and variable displacement pump?

In the fixed displacement pump, the pump displacement cannot be varied by any means. But in the variable displacement pump, the pump displacement can be varied by any arrangement.

9. Why gear pump cannot be used as a variable displacement pump?

In the gear pump, the displacement depends on the design parameters of gears and they cannot be changed. So the displacement cannot be varied in gear pumps.

10. How can the unbalanced vane pump be used as a variable displacement pump?

In unbalanced vane pump, the displacement depends on eccentricity between rotor and cam ring. By mechanically varying the eccentricity, the pump delivery is varied.

11. What is a pressure compensated vane pump and how does it work?

In the unbalanced vane pump, the displacement can be varied by varying the eccentricity. By a compensator piston arrangement, the eccentricity is varied depending on the system pressure thereby pump delivery is varied. This pump is called pressure compensated vane pump.

12. What is meant by a balanced design vane pump?

In balanced vane 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.

13. Name the two basic types of piston pumps.

(i) Axial piston pump (ii) Radial piston pump.

14. How can the displacement of an axial piston pump be varied?

In axial piston pumps, by varying the stroke length the displacement can be varied. In bent axis type, by varying the angle between cylinder block and drive shaft centerline, the stroke length can be varied. In swash plate type by varying the swash plate angle the stroke length can be varied.

15. Define volumetric efficiency of a pump.

Volumetric efficiency of pump = (Actual flow rate produced by the pump / Theoritical flow rate the pump should produce)

16. Define mechanical efficiency of a pump.

Mechanical efficiency m = Theoritical power required to operate the pump / Actual power delivered to the pump

19. Draw the graphic symbols for the following pump types.

(i) Fixed displacement (ii) Variable displacement (iii) Pressure compensated (iv) Bidirectional.

20. What is a hydraulic actuator?

The actuator is a hydraulic element which converts the pressure energy of the fluid into mechanical energy.

21. What are the types of hydraulic actuators?

There are three basic types of hydraulic actuator,
(i) Hydraulic motor–continuous rotary motion
(ii) Semi-rotary actuator-limited angle movement
(iii) Hydraulic cylinder-linear motion.

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

The motors 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.

23. Name the construction types of hydraulic motors available.

(i) Gear type hydraulic motors (ii) Vane type hydraulic motors (iii) Piston type hydraulic motors.

24. Where are external gear motors used?

External gear motors are used when relatively high speed and low torque is needed.

25. What is a semi-rotary actuator?

Semi-rotary actuators convert pressure energy into torque, which turns through only limited angle.

26. List few applications of semi-rotary actuator?

The semi-rotary actuators are used for lifting, tilting, opening, closing, indexing, swinging and bending applications.

29. 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.

30. What are the advantages of double acting cylinder over a single acting cylinder?

(i) 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 a double acting cylinder, so they perform work in both directions.
(ii) In a single acting cylinder, the stroke is limited by the compressed length of the spring. But in principle, the stroke is unlimited in a double acting cylinder.
(iii) 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.

31. What is cylinder cushioning?

Due to the inertia 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 retarded or cushioned during the last portion of the stroke. This is known as cylinder cushioning.

32. For what application, 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.

33. 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.

34. What is a telescoping cylinder? When is it normally used?

A telescoping cylinder is a cylinder employing several pistons which telescope into each other. This cylinder is used where a relatively long working stroke is needed for a short cylinder length.

35. Name the types of cylinder mountings.

(i) Fixed centerline mounts

• Tie rod end
• Rod end flange
• Blind end flange
• Centerline lugs

(ii) Fixed non-centerline mounts

• End lug mounts Side
• lug mounts Integral
• key mounts Flush
• mounts

(iii) Pivoted centerline mounts

• Rod end trunnion
• Blind end trunnion
• Clevis
• Center trunnion

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