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Hydralics > pump service and fundamentals questions > Flashcards

pump service and fundamentals questions Flashcards

1
Q

hydraulic pumps that are able to change their pumping chambers are called

A

variable displacement pumps

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2
Q

a pump termed reversible is able to

A

reverse the direction of oil flow internally through the pump

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3
Q

as pump outlet pressure increases the pumps internal leakage decreases

A

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

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4
Q

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

A

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

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5
Q

what is the function of the trap in a gear pump pressure plate

A

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

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6
Q

why is some internal leakage necessary with all hydraulic pumps

A

lubrication of moving parts

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7
Q

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

A

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

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8
Q

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

A

internal leakage

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9
Q

three general guidelines to follow during pump disassembly

A

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

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10
Q

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

A

cavitation

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11
Q

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

A

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

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12
Q

four tasks to be preformed when pump is changed

A

change oil change filters clean oil tank clean out lines

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13
Q

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

A

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

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14
Q

when the internal volume of a hydraulic pump increases the pressure

A

decreases

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15
Q

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

A

true

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16
Q

pumps that have a constant pumping chamber are known as

A

fixed displacement

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17
Q

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

A

variable displacement pumps

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18
Q

three categories of pump efficiency are

A

mechanical . volumetric . overall

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19
Q

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

A

false . internal leakage will increase with pump outlet pressure

20
Q

overall pump efficiency is

A

a comparison of pump input and output power

21
Q

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

A

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

22
Q

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

A

have the oil flow through the pump reversed

23
Q

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

A

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

24
Q

pressure plates in vane pumps control

A

rotor side clearance

25
Q

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

A

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

26
Q

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

A

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

27
Q

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

A

it will move to a zero displacement position

28
Q

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

A

a servo system

29
Q

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

A

outlet oil pressure

30
Q

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

A

centrifugal force

31
Q

how can the rotating piston radial piston pump be made variable

A

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

32
Q

how can a radial cam piston pump be made variable

A

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

33
Q

formula to calculate flow rate of a pump

A

pump displacement x rpm then divided by 1000cm3

34
Q

what is mechanical efficiency

A

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

35
Q

what is volumetric efficiency

A

the expression of how effective a pump can generate flow

36
Q

how is volumetric efficiency calculated

A

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

37
Q

what is pump slip

A

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

38
Q

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

A

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

39
Q

what is overall efficiency

A

comparing input power with the power delivered by the pump

40
Q

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

A

increased internal leakage and higher mechanical losses due to internal loading

41
Q

where dose overall efficiency peak in a hydraulic pump

A

at normal operation ranges

42
Q

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

A

to ensure all moving parts have access to oil

43
Q

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

A

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

44
Q

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

A

spur . helical . herring bone

45
Q

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

A

non hunting spur cut gears

46
Q

what is cavitation most commonly caused by

A

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

Hydralics (12 decks)

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