190301b

Question 1

T/F external gear pumps are made to operate regardless of direction of rotation

Answer 1

False

Question 2

One disadvantage of a gear pump is

Answer 2

It can only have a fixed displacement

Question 3

What are 2 disadvantages of vane pumps?

Answer 3

more expensive to purchase and repair than a gear pump, also more susceptible to contamination damage

Question 4

On a vane type pump, what is the component that holds the vane blades?

Answer 4

Vane rotor

Question 5

When the internal volume of a hydraulic pump increases the pressure….

Answer 5

Decreases

Question 6

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

Answer 6

decreases

Question 7

Hydraulic oil is forced out of the pump when the volume of the pumping chamber is
decreased.T/F

Answer 7

true

Question 8

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

Answer 8

fixed

displacement pumps.

Question 9

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

Answer 9

variable displacement pumps

Question 10

A pump termed reversible is able to:

Answer 10

reverse the direction of oil flow through the pump.

Question 11

Three (3) categories of pump efficiency are:

Answer 11

a) mechanical efficiency,
b) volumetric efficiency and
c) overall efficiency.

Question 12

As pump outlet pressure increases, the pump’s internal leakage decreases.T/F

Answer 12

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

Question 13

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 pumps.

Answer 13

all of the above responses are correct

Question 14

Why is some internal leakage necessary within all hydraulic pumps?

Answer 14

Internal leakage lubricates moving pump parts.

Question 15

The two (2) factors that determine the amount of internal leakage in a pump are:

Answer 15

a) the pressure difference between the pump inlet and outlet ports
b) the amount of internal clearance within the pump.

Question 16

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

Answer 16

have the flow through the pump reversed.

Question 17

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 17

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

Question 18

Pressure plates are used in vane pumps to control the clearance between the tip of the
vane and the cam ring.T/F

Answer 18

false; Pressure plates are used in vane pumps to control rotor side clearance.

Question 19

A variable displacement vane pump changes its displacement by:

Answer 19

changing the eccentricity between the rotor and cam ring centres.

Question 20

List the two (2) forces that act on the vanes of a typical vane pump.

Answer 20

a) centrifugal force

b) outlet oil pressure acting on the underside of the vane.

Question 21

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

Answer 21

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 22

List two (2) reasons why oil pressure from the pumping chambers of an axial piston
pump is connected to the piston shoes.

Answer 22

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

Question 23

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

Answer 23

internal leakage.

Question 24

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.T/F

Answer 24

true

Question 25

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

Answer 25

servo

Question 26

A variable displacement pump that reduces its flow rate in relation to outlet pressure is called?

Answer 26

A pressure compensated pump

Question 27

Direction of rotation on a unidirectional pump is often shown by?

Answer 27

An arrow in the cast of the pump housing

Question 28

You can change the direction of oil flow by simply changing the vanes. T/F

Answer 28

False. Depending on the pump make, you can disassemble the pump and change the orientation of the cam ring.

Question 29

What are the 3 kinds of piston pumps?

Answer 29

Radial
Axis
Bent axis

Question 30

A piston pump is the most efficient, why?

Answer 30

They have closer tolerances, least amount of internal leakage, and can be operated at higher pressures.

Question 31

What prevents high pressure oil from being pumped into the pumping chamber?

Answer 31

A check valve on the outlet ports.

Question 32

What are the 2 designs of radial piston pumps?

Answer 32

Rotating cam and rotating piston.

Question 33

In a radial piston pump, what assists with the variable displacement?

Answer 33

Hydraulic oil acts against the pistons holding them off of the cam. The more pressure the farther away from the cam they are.

Question 34

What is one characteristic of an axial piston pump?

Answer 34

The pistons are arranged so that the centreline is parallel with the pump driveshaft.
The pump driveshaft is connected to and drives the cinder barrel.
The pistons are closely fitted into the cylinder barrel and slide on a swash plate.
Swash plate angle determines stroke.
They are built with an odd number of pistons.
They can be fixed or variable displacement.

Question 35

What is the cylinder and barrel called?

Answer 35

The rotating group.

Question 36

What holds the pistons against the swash plate?

Answer 36

A shoe plate ensures the pistons stay against the swash plate.