VEERAPANDIAN.K , Assistant Professor: Two Marks Q&A

1. What are the four important factors that should be considered while designing a fluid power circuit?

1. Safety of operation,

2. Performance of desired function,

3. Efficiency of operation, and

4. Cost.

2. What is the use of a regenerative circuit ?

A regenerative circuit is used to speed up the extending speed of the double-acting cylinder.

3. Why is the load-carrying capacity of a regenerative cylinder small when the piston rod area is small?

Regenerative cylinder extending load-carrying capacity = Fload = P.A,

Therefore when piston area (A,) is small, then the load-carrying capacity of the regenerative cylinder will also be small.

4. Why is extension stroke faster than retraction stroke in a regenerative circuit ?

This is because oil flow from the rod end regenerates with the pump flow to provide a total flow rater, which is greater than the pump flow rate to the blank end of the cylinder.

5. What do you mean by sequencing of cylinders ? (or) What is a sequencing circuit?

In many applications, the operation of two hydraulic cylinders is required to be performed in sequence one after another. This is known as sequencing of cylinders.

6. What is the advantage of using sequencing circuit?

Sequencing circuits automatically move actuators in a predetermined sequence.

7. State the need for synchronization of hydraulic cylinders.

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.

8. When synchronizing circuit is required?

Synchronizing circuit is needed to accomplish the identical task from the cylinders at the same rate.

9. What is the purpose of a fail-safe circuit ?

Fail safe circuit is designed to safeguard the operator, the machine, and the workpiece. It prevents any possible injury to the operator or damage to the machine and the workpiece.

10. Where speed control circuits are required?

Speed control circuits are required to reduce the speed of cylinder from maximum speed based on selected size of final control valve to the nominal speed depending on the applications.

11. Differentiate between meter-in and meter-out circuits with respect to speed control circuits.

• In meter-in circuit, the flow control valve is located in between the pump and the actuator (piston side connection). Thereby, it controls the amount of fluid flowing into the cylinder.

• In meter-out circuit, the flow control valve is located in between the actuator (rod side connection) and the oil reservoir. Thereby, it controls the fluid flowing out of the actuator.

12. What is “meter-in” circuit? What is its limitation?

• The 'meter-in' circuit controls the amount of fluid flowing into the cylinder.

• Limitation: 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 system, meter-in circuit is not preferred.

13. What is "meter-out" circuit? What are its limitations?

• The 'meter-out' circuit controls the fluid flowing out of the actuator.

• Limitation: 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.

14. What is the function of bleed-off circuit ?

• Bleed-off circuit is used to control the flow of fluid by bleeding off the excess not needed by the actuator.

• In bleed-off circuit, the flow control valve is located in between the pressure line and return line (either before the DC valve or after the DC valve).

15. What are hydropneumatic circuits ?

In some applications, the hydraulic and pneumatic circuits are coupled to get best use of the advantages of both oil and air mediums. These combination circuits are known as hydropneumatic or pneumohydraulic circuits.

16. List any four advantages of employing pneumo-hydraulic circuits.

1. Using the combination circuit, the quick action of air and smooth, high pressure action of oil can be blended.

2. The hydropneumatic circuits will reduce space requirements.

3. These circuits increase the performance of the equipment.

4. These circuits will reduce initial and maintenance cost of original equipment.

17. What is meant by hydrostatic transmission system?

Hydrostatic transmission is special case of energy transmission system where the mechanical energy of the input drive shaft is converted into pressure energy in the nearly incompressible working fluid and then reconverted into mechanical energy at the output shaft.

1. What is the function of an accumulator ?

An accumulator is a pressure storage reservoir in which a non-compressible hydraulic fluid is retained under pressure from an external source.

2. Highlight the need of using an accumulator in hydraulic circuits.

• The function of hydraulic accumulator is analogous to that of the flywheel of a reciprocating engine and a capacitor in an electronic circuit

• In hydraulic systems like crane or lift, the liquid under pressure needs to be supplied only during the upward motion of the load. This energy is supplied from hydraulic accumulator. But when the lift is moving downward, no large external energy is required and during that period the energy from the pump is stored in the accumulator.

3. What electrical device is accumulator analogous to ?

The function of hydraulic accumulator is analogous to that of a capacitor in an electrical circuit.

4. Name the basic types of accumulators used in hydraulic systems.

1. Weight-loaded (or dead-weight) accumulators,

2. Spring-loaded accumulators, and

3. Gas-loaded accumulators.

5. What are the uses/functions of accumulators? (or) List any four applications of accumulators.

Accumulators are used as :

(i) Leakage compensator,

(ii) Auxiliary power source,

(iii) Emergency power source,

(iv) Hydraulic shock absorber,

(v) Fluid make-up device,

(vi) `Holding device, etc.

6. Which type of accumulator operates at constant pressure? How can the pressure be changed?

• Weight-loaded (or dead-weight) accumulator operates at constant pressure.

• The pressure can be changed by changing the dead-weight of the accumulator.

7. Why weight loaded type accumulator is undesirable for mobile equipment?

Because of the weight loaded type accumulator is very heavy; not portable; and do not respond quickly to changes in the system demand.

8. What type of gas is used in gas-loaded accumulators? Why is oxygen not used for this purpose?

• The inert gas such as nitrogen gas is used in gas-loaded accumulator.

• The air or oxygen are not used due to the danger of explosion.

9. Explain briefly the non-separator type gas loaded accumulator.

In the non-separator type gas loaded accumulator, pressurisation is achieved by introducing a pressurizing gas into a container above the oil level. When the system pressure increases, the oil enters through oil port and pushes the gas. The reduction of volume of gas increases its pressure. This gas pressure is used as the potential energy to force the oil out when it is required in the circuit.

10. What is meant by sizing of accumulators? (or) What is meant by the term 'capacity' of an accumulator?

The maximum amount of energy that the accumulator can store is known as the capacity of the accumulator.

11. What are three significant accumulator operating conditions ?

1. Recharging condition.

2. Charging (the fluid to maximum pressure) condition, and

3. Discharging (the fluid to minimum pressure) condition.

12. What is the function of a pressure intensifier ? (or) What is an intensifier?

Pressure intensifier, also known as pressure booster, is used to compress the liquid in a hydraulic system to a value above the pump discharge pressure.

13. What is gained and what is lost in an intensifier?

In intensifier, pressure is gained and the volume is lost.

14. What electrical device is pressure intensifier analogous to ?

Pressure intensifier is analogous to a step-up electrical transformer.

15. List the applications of an intensifier.

Intensifiers find most useful applications where the output pressure requirements are much higher than that are obtainable from a pump. Typical applications include punching presses, riveting machines, spot-welders, and in many high-pressure testing machines such as tubing fixtures for testing bursting pressures and high pressure holding fixtures.

16. What is meant by air-oil intensifier?

Air-over-oil intensifier is used for driving a cylinder over a large distance at a low pressure and then over a small distance at high pressure (such as in punch press application).

17. Define the term intensifier ratio.