Hydraulic Pump Fundamentals

Question 1

When the internal volume of a hydraulic pump increases, the pressure:

Answer 1

Decreases

Question 2

Pumps that have a constant pumping chamber volume are known as:

Answer 2

Fixed displacement pumps

Question 3

A pump termed reversible is able to:

Answer 3

Reverse the direction of oil flow through the pump.

Question 4

A hydraulic pump with a displacement of 135 cm^3 rev is being driven at 2000 rpm. A flow meter installed in the pump outlet line indicates that the pump is delivering 254L/Min. What is the pumps volumetric efficiency?

Answer 4

94%

Question 5

Overall pump efficiency:
A. Is a comparison of pump input and output power.
B. Accounts for both mechanical and flow losses.
C. Is greater for piston than gear pump
D. All of the above.

Answer 5

D. All of the above.

Question 6

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

Answer 6

A. The pressure difference between pump inlet and outlet ports.
B. The amount of internal clearance in the pump.

Question 7

State the main difference between the cam ring used in an unbalanced vane pump and the cam ring used in a balanced vane pump.

Answer 7

The cam ring used in an unbalanced van pump has a circular bore while the cam ring bore in a balanced vane pump is elliptical.

Question 8

A variable displacement vane pump changes its displacement by:

Answer 8

Changing the eccentricity between the rotor and the cam ring centers.

Question 9

Why must the force exerted by the vanes against the cam ring of a high performance vane pump be reduced?

Answer 9

Because high vane force will cause the film of lubricating oil between the vane tip and the cam ring to be squeezed out resulting in metal to metal contact and very rapid wear.

Question 10

The oil that gathers in the case of an axial piston pump comes from:

Answer 10

Internal leakage.

Question 11

A hydraulic control system that copies the movement of the control lever is called a _______ system.

Answer 11

Servo

Question 12

Hydraulic oil is forced out of the pump when the volume of the pumping chamber is decreased.
True or False

Answer 12

True

Question 13

Hydraulic pumps that are able to change the capacity of their pumping chambers are called:

Answer 13

variable displacement pumps

Question 14

Three categories of pump efficiency are:

Answer 14

Mechanical efficiency.
Volumetric efficiency.
Overall efficiency.

Question 15

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

Answer 15

False

Question 16

Why is some internal leakage necessary within all hydraulic pumps?

Answer 16

Internal leakage lubricates moving pump parts.

Question 17

A unidirectional pump that is driven opposite to its intended direction will:

Answer 17

Have the flow thru the pump reversed.

Question 18

Pressure plates are used in vane pumps to control the clearance between the tip of the vane and the cam ring.
True or False

Answer 18

False

Question 19

List the two forces that act on the vanes of a typical vane pump.

Answer 19

Centrifugal forces.

Outlet oil pressure acting on the underside of the vane.

Question 20

List two reasons why oil pressure from the pumping chambers of an axial piston pump is connected to the piston shoes.

Answer 20

To lubricate the ball and socket joints between the piston and the shoe as well as the contact area between the shoe and the swash plate.
Balance the piston by offsetting the force generated by the pressure in the pumping chamber.

Question 21

A pressure compensated axial piston pump of the pressure limiting type will move its swash plate to the zero displacement position when system maximum system pressure is achieved.
True or False.

Answer 21

True.