I - Hydraulic System Components: Pumps, Valves, and Cylinders

Question 1

A hydraulic pump with a displacement of 135 cm3/rev is driven at 2000 rpm. A flowmeter installed in the pump outlet line indicates that the pump delivers 254 L/min. What is the pump’s volumetric efficiency?

Answer 1

94%

Question 2

True or False: As pump outlet pressure increases, the pump’s internal leakage decreases.

Answer 2

False; As pump outlet pressure increases, the pump’s internal leakage also increases.

Question 3

Why is some internal leakage necessary within all hydraulic pumps?

Answer 3

Internal leakage lubricates moving pump parts.

Question 4

The two factors that determine the amount of internal leakage in a pump are:

Answer 4

The pressure difference between the pump inlet and outlet ports and the amount go internal clearances within the pump.

Question 5

The most common cause of pitted erosion on the internal surfaces of the pump is:

Answer 5

Cavitation.

Question 6

The hydraulic pump converts (?) energy to (?) energy.

Answer 6

Mechanical and hydraulic.

Question 7

True or False: A hydraulic pump creates pressure.

Answer 7

False; The hydraulic pump does not create pressure; it creates flow. The resistance to pump flow creates pressure.

Question 8

The most important characteristic of a non-positive displacement pump is that:

Answer 8

Inlet and outlet ports are hydraulically connected.

Question 9

Which of the following is a non-positive displacement pump: gear pump, vane pump, piston pump, or engine water pump.

Answer 9

Engine water pump.

Question 10

The main advantage of a positive displacement pump over a non-positive displacement pump is that:

Answer 10

Flow does not decrease significantly as pressure increases.

Question 11

The two factors that affect pump flow rate are:

Answer 11

Pump displacement and Input shaft.

Question 12

Pump displacement refers to:

Answer 12

The volume of liquid that a pump delivers in one revolution.

Question 13

A 100 cm3/rev pump that is driven at 1500 rpm produces a flow rate of:

Answer 13

150 L/min

Question 14

The term used to express the amount of power required to overcome a pump’s internal friction is:

Answer 14

Mechanical efficiency.

Question 15

The theoretical flow rate of a pump is 285 L/min. What is the pump’s actual flow rate if the pump has a volumetric efficiency of 92%?

Answer 15

262.20 L/min

Question 16

Cavitation occurs in a hydraulic pump when:

Answer 16

Inlet pressure falls too low.

Question 17

Pump inlet pressure is affected by:

Answer 17

Pump inlet restriction and pump drive speed

Question 18

The most common cause of hydraulic pump aeration is:

Answer 18

Air leakage on the inlet side of the pump.

Question 19

When a three-stage telescoping hydraulic cylinder is operated, the greatest force is generated when the:

Answer 19

First stage is extended.

Question 20

Double-acting hydraulic cylinders differ from single-acting cylinders on that they:

Answer 20

Hydraulically extend and retract.

Question 21

True or False: In its normal position, a normally closed pressure control valve blocks oil flow from its inlet port to its outlet port.

Answer 21

True.

Question 22

The term that describes the pressure when a direct-acting, normally closed pressure relief vale initially begins to open is:

Answer 22

Cracking pressure.

Question 23

The term that describes the pressure when a direct-acting, normally closed pressure relief valve is fully open is:

Answer 23

Full flow pressure.

Question 24

Single-acting hydraulic cylinders:

Answer 24

hydraulically actuate in one direction.

Question 25

Single-acting hydraulic cylinders are returned by:

Answer 25

Some external force.