pump service and fundamentals questions

Question 1

hydraulic pumps that are able to change 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 internally through the pump

Question 3

as pump outlet pressure increases the pumps internal leakage decreases

Answer 3

false . as pump outlet pressure increases the pumps internal leakage also increases

Question 4

why do manufacturers make gear pumps with aluminium housings allowing the gears to cut a gear path in the housing during break in

Answer 4

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

Question 5

what is 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 to escape as they come into mesh

Question 6

why is some internal leakage necessary with all hydraulic pumps

Answer 6

lubrication of moving parts

Question 7

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

Answer 7

to lubricate the ball socket between the piston and the shoe as well as the contact area between the shoe and the swash plate . also balancing 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

three general guidelines to follow during pump disassembly

Answer 9

mark pump housing to return to original location . determine the direction of driveshaft rotation . be sure to keep mated components together and in original position

Question 10

what is the most common cause of pitted erosion on the internal surface of a pump

Answer 10

cavitation

Question 11

what are three reasons that could cause a pump to have lack of lubrication

Answer 11

improper oil for application . low oil reservoir level causing inlet to be uncovered . severe aeration

Question 12

four tasks to be preformed when pump is changed

Answer 12

change oil change filters clean oil tank clean out lines

Question 13

why should the adjustment of pressure controls be backed off prior to starting a machine after the hydraulic pump has been replaced

Answer 13

to prevent overloading of the pump in the event controls have been misadjusted prior to pump replacement

Question 14

when the internal volume of a hydraulic pump increases the pressure

Answer 14

decreases

Question 15

hydraulic oil is forced out of a pump when the volume of the pumping chamber is decreased true or false

Answer 15

true

Question 16

pumps that have a constant pumping chamber are known as

Answer 16

fixed displacement

Question 17

hydraulic pumps that are able to change the displacement of their pumping chambers are known as

Answer 17

variable displacement pumps

Question 18

three categories of pump efficiency are

Answer 18

mechanical . volumetric . overall

Question 19

as the pumps outlet pressure increases the pumps internal leakage decreases true or false

Answer 19

false . internal leakage will increase with pump outlet pressure

Question 20

overall pump efficiency is

Answer 20

a comparison of pump input and output power

Question 21

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

Answer 21

pressure difference between pump inlet and outlet pressure . amount of internal clearance within the pump

Question 22

a unidirectional pump that is driven in the opposite direction it is intended to will

Answer 22

have the oil flow through the pump reversed

Question 23

what are the main differences between the cam ring used in an unbalanced to a balanced vane pump design

Answer 23

the cam ring in an unbalanced uses a circular bore while the cam ring in a balanced design uses an elliptical design

Question 24

pressure plates in vane pumps control

Answer 24

rotor side clearance

Question 25

what are two forces acting on the vanes of a typical vane pump

Answer 25

centrifugal force and oil pressure acting on the underside of the vanes

Question 26

why must the force exerted by the vanes acting on the cam ring in high performance pumps be reduced

Answer 26

to avoid the vane breaking the film of oil separating them from the cam ring . resulting in metal to metal contact

Question 27

when an pressure limiting axial piston pump reaches maximum system pressure what will the swash plate do

Answer 27

it will move to a zero displacement position

Question 28

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

Answer 28

a servo system

Question 29

with the intra vane design what pressure is acting on the space in the slot above the intra vane

Answer 29

outlet oil pressure

Question 30

in a rotating piston radial piston pump what force is holding the pistons against the cam ring inside the pump

Answer 30

centrifugal force

Question 31

how can the rotating piston radial piston pump be made variable

Answer 31

by adjusting the relationship between the cylinder block and the cam ring thus changing the length of stroke

Question 32

how can a radial cam piston pump be made variable

Answer 32

by sending outlet oil back into the pump housing acting on the pistons around the cam and limiting their stroke

Question 33

formula to calculate flow rate of a pump

Answer 33

pump displacement x rpm then divided by 1000cm3

Question 34

what is mechanical efficiency

Answer 34

an expression of how much power is required to overcome the internal friction of the pump

Question 35

what is volumetric efficiency

Answer 35

the expression of how effective a pump can generate flow

Question 36

how is volumetric efficiency calculated

Answer 36

by dividing actual flow rate of the pump by theoretical flow rate then x 100 to get a volumetric efficiency %

Question 37

what is pump slip

Answer 37

a term that refers to the amount of oil leaking from outlet to inlet side of a pump

Question 38

what ae two conditions that will allow slippage to increase in a hydraulic pump

Answer 38

the amount of wear a pump has and the amount of pressure difference from outlet to inlet

Question 39

what is overall efficiency

Answer 39

comparing input power with the power delivered by the pump

Question 40

what would cause a loss of overall efficiency at the max rage of operation in a hydraulic pump

Answer 40

increased internal leakage and higher mechanical losses due to internal loading

Question 41

where dose overall efficiency peak in a hydraulic pump

Answer 41

at normal operation ranges

Question 42

why must all hydraulic pumps be pre lubricated prior to pump start up

Answer 42

to ensure all moving parts have access to oil

Question 43

where is the trap located on a pressure plate of a gear pump

Answer 43

on the outlet side of the pump and must be rotated 180 degrees if driveshaft rotation is reversed

Question 44

what are the three types of gears available in a gear pump

Answer 44

spur . helical . herring bone

Question 45

what are the most common type of gears used in a gear pump

Answer 45

non hunting spur cut gears

Question 46

what is cavitation most commonly caused by

Answer 46

improper oil . restrictions in the inlet side . over speeding f the pump