190301c

Question 1

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

Answer 1

variable displacement pumps.

Question 2

A pump termed reversible is able to:

Answer 2

reverse the direction of oil flow through the pump

Question 3

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

Answer 3

false;

Question 4

Why do manufacturers of gear pumps with aluminum housings allow the gears to cut
a gear path into the pump housing during break-in?

Answer 4

To provide good volumetric efficiency by keeping gear tip clearance to a minimum.

Question 5

State the function of the trap in a gear pump pressure plate.

Answer 5

The trap provides an escape path for oil trapped between the gear teeth as they come
into mesh.

Question 6

Why is some internal leakage necessary within all hydraulic pumps?

Answer 6

Internal leakage lubricates moving pump parts.

Question 7

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

Answer 7

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.
b) Balance the piston by offsetting the force generated by the pressure in the
pumping chamber.

Question 8

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

Answer 8

internal leakage.

Question 9

List three (3) general guidelines that should be observed when disassembling a
hydraulic pump.

Answer 9

a) Mark pump housings so that they can be returned to their proper location during
assembly.
b) Determine the correct direction of driveshaft rotation for unidirectional pumps so
that the pump can be returned to the proper rotation on assembly.
c) Be sure to keep mated components (such as gear sets, pistons and barrels)
together so that they can be returned to their original positions.

Question 10

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

Answer 10

cavitation.

Question 11

List three (3) reasons that could cause a hydraulic pump to lack lubrication.

Answer 11

a) using improper hydraulic oil for the application and climatic conditions
b) low reservoir oil level which causes the pump inlet to become uncovered
c) severe aeration

Question 12

List four (4) tasks that should be performed when a hydraulic pump is installed to
ensure that the system is clean enough to ensure good pump service life:

Answer 12

a) The hydraulic oil may need to be changed or filtered to remove contamination.
b) Hydraulic filters must be serviced.
c) The hydraulic reservoir must be thoroughly cleaned.
d) The complete system may have to be flushed.

Question 13

Why should the adjustment of system pressure controls be backed off prior to starting
a machine in which the hydraulic pump has been replaced?

Answer 13

Pressure controls are backed off to prevent overloading the pump in the event that the
pressure controls have been misadjusted prior to pump replacement.

Question 14

Pump Cavitation failure is most commonly caused by?

Answer 14

Using improper hydraulic oil
Restrictions in the pump inlet line
Excessive pump driveshaft speed

Question 15

Evidence of a lack of lubrication is shown by

Answer 15

Heavy wear of surfaces of moving parts
Blue colouring
Smearing and metal transfer between contacting surface
Pump seizure

Question 16

How are most multiple pump configurations driven?

Answer 16

With a common inlet (driveshaft)

Question 17

On external gear hydraulic pumps, the gears come into mesh at the inlet side. T/F

Answer 17

False; The gears must come into mesh at the outlet.

Question 18

What is very important before disassembling a pump?

Answer 18

You must determine the direction of rotation of the shaft. Often marked with arrows.

Question 19

On a vane pump there is a larger inlet than an outlet. T/F

Answer 19

True.

Question 20

What is the function of the pressure plate?

Answer 20

They keep the internal clearances to a minimum, limiting the internal leakage.

Question 21

What should you consider when examining a vane pump?

Answer 21

Condition of parts.
Type and condition of oils and filters.
Operating conditions at time of failure.
Severity of job application. ( machine too small for job)
Amount of time pump has been in service.
Previous failures and repairs.