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HET3 Hydraulics 190301 > 190301b > Flashcards

Flashcards in 190301b Deck (36):
1

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

False

2

One disadvantage of a gear pump is

It can only have a fixed displacement

3

What are 2 disadvantages of vane pumps?

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

4

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

Vane rotor

5

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

Decreases

6

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

decreases

7

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

true

8

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

fixed
displacement pumps.

9

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

variable displacement pumps

10

A pump termed reversible is able to:

reverse the direction of oil flow through the pump.

11

Three (3) categories of pump efficiency are:

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

12

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

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

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.

all of the above responses are correct

14

Why is some internal leakage necessary within all hydraulic pumps?

Internal leakage lubricates moving pump parts.

15

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

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

16

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

have the flow through the pump reversed.

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.

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.

18

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

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

19

A variable displacement vane pump changes its displacement by:

changing the eccentricity between the rotor and cam ring centres.

20

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

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

21

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

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.

22

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

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.

23

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

internal leakage.

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

true

25

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

servo

26

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

A pressure compensated pump

27

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

An arrow in the cast of the pump housing

28

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

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

29

What are the 3 kinds of piston pumps?

Radial
Axis
Bent axis

30

A piston pump is the most efficient, why?

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

31

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

A check valve on the outlet ports.

32

What are the 2 designs of radial piston pumps?

Rotating cam and rotating piston.

33

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

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

34

What is one characteristic of an axial piston pump?

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.

35

What is the cylinder and barrel called?

The rotating group.

36

What holds the pistons against the swash plate?

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