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Hydralics > Pumps > Flashcards

Pumps Flashcards

1
Q

major types of pumps are

A

gear . vane . piston

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2
Q

hydraulic pumps convert

A

mechanical energy to hydraulic

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3
Q

how dose a pump convert energy

A

by taking energy from a prime mover and generating flow through a system

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4
Q

what is the basic pumping principle

A

increasing the internal volume during the intake cycle creates a low pressure that allows atmospheric head pressure to push oil into the pumps inlet

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5
Q

pumps that have a constant pumping chamber volume will deliver

A

the same amount of fluid with every revolution with a constant input rpm

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6
Q

on a gear pump the volume of oil delivered in one revolution will be the sum of capacities of

A

all the gear tooth pockets on both the driven and drive gears

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7
Q

why is a internal gear pump a fixed displacement pump

A

because the capacity of each gear tooth cannot change therefore the pumps displacement cannot change

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8
Q

on a fixed displacement vane pump the volume of oil will be the

A

sum of the capacity of the vane pockets per revolution

the capacity cannot change therefor the displacement cannot change

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9
Q

on a fixed displacement axial piston pump the volume of oil delivered in one revolution will be

A

the sum of all the pumping chambers per revolution

the volume of the chambers cannot change therefor the displacement cannot change

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10
Q

variable displacement pumps

A

are able to change the volume of the pumping chambers therefor making them variable displacement

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11
Q

why can gear pumps not be variable in displacement

A

because they are built in a housing that is unable to change its pocket size therefor making them unable to be variable displacement

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12
Q

how can vane pumps be variable displacement

A

the cam ring around the vane pockets can be moved changing the pocket size allowing for different displacement to occur

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13
Q

what are the three different designs of piston pumps

A

axial . bent axial and radial

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14
Q

how do piston pumps have variable displacement

A

by changing the stroke length of the pistons

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15
Q

axial piston pumps have

A

pistons that are parallel with the drive shaft . the pistons are in a rotating cylinder block and the other end has a shoe that slides on a swash plate

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16
Q

changing the swashplate angle will result in what on a piston pump

A

changing the length of the pistons stroke . maximum angle means maximum flow

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17
Q

bent axial piston pumps have

A

pistons that are parallel with the drive shaft and the pistons are in a rotation cylinder block the other end is held to the driveshaft in a ball and socket design

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18
Q

how do you change displacement on a bent axial piston pump

A

by moving the cylinder block in relation to the drive shaft to create different angles

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19
Q

how dose a reversible displacement pump change directions

A

they are able to reverse the path of oil flow internally by moving the swash plate

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20
Q

where would you most likely use a reversible displacement pump

A

as a hydrostatic transmission ( HST )

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21
Q

what could result if maximum pump input speed is exceeded

A

pump cavitation . because an overspeed condition dose not allow enough time for oil to completely fill the inlet of the pump

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22
Q

what will pump efficiency specifications tell you

A

how well the pump is converting mechanical energy to hydraulic energy

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23
Q

what are the three categories of pump efficiency

A

mechanical . volumetric . overall

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24
Q

mechanical efficiency is

A

an expression of the amount of power required to overcome the internal friction of the pump

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25
Q

volumetric efficiency is

A

how effectively a hydraulic pump generates flow

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26
Q

how do you calculate volumetric efficiency of a pump

A

by comparing theoretical and actual flow rate

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27
Q

what do all hydraulic pumps have

A

internal leakage

28
Q

why is internal leakage important

A

because it is used to lubricate the internal workings of the pump

29
Q

what is pump slip

A

when oil leaks from the outlet side of the pump to the inlet side

30
Q

what two things contribute to pump slippage

A

increases in pressure differential between outlet and inlet side of pump and pump wear

31
Q

overall efficiency is

A

comparing input power with the power the pump will deliver

32
Q

what will cause a loss of overall efficiency at higher operating pressures

A

increased internal leakage and higher mechanical losses caused by internal loading

33
Q

three advantages of an external gear pump

A

less complex . least expensive . more rugged more tolerant of contamination

34
Q

two disadvantages of external gear pumps

A

have the lowest maximum operating pressures . variable displacement designs are not available

35
Q

basic components of a external gear pump

A

drive gear . driven gear . housing . support bearings . o rings . internal pressure plates

36
Q

why are external gear pumps considered unbalanced pumps

A

because the force acting on the outlet side of the pump is not counteracted by the inlet side of the pump

37
Q

what is the purpose of the pressure plates in an external gear pump

A

to maintain good volumetric efficiency as the pressure of the pump increases

38
Q

what is a unidirectional pump

A

operates in only one direction

39
Q

what is the most identifiable feature of a bi directional pump

A

inlet and outlet ports are the same size . proper rotation is determined by looking and seeing what direction the gears come out of mesh

40
Q

advantages of a vane pump

A

increased precision make them more efficient and operate at higher pressures . can be built to have variable displacement

41
Q

disadvantages of a vane pump

A

more expensive . more susceptible to contamination damage

42
Q

components of a three piece vane pump

A

mounting pad contains the port and is located on the front housing . center housing is machined with an elliptical opening known as a cam ring . back housing is precision machined to seal the rotor and vanes

43
Q

components of a two piece vane pump

A

front housing supports the drive shaft and outlet ports . the rear housing contains the inlet port and houses the pumping components . pumping components are assembled as a complete unit known as a cartridge

44
Q

vane pump rotor

A

is a cylindrical component and splined onto the drive shaft of the pump also houses the vanes

45
Q

vane pump vanes

A

are closely fitted into slots on the rotor and when centrifugal force or high pressure oil acts on them they contact the cam ring

46
Q

two common types of vane tips are

A

rounded and bevelled

47
Q

what two forces act on the vanes of a vane pump

A

outlet pressure and centrifugal force

48
Q

what benefits do a intra vane provide

A

helps reduce loading on the vane as it passes through the inlet side of the pump preventing contact without lubrication

49
Q

cam ring of a vane pump provides

A

the surface on witch the vanes run on

50
Q

elliptical cam rings are

A

used in balanced vanes pumps where higher pressures may be present but are a fixed displacement

51
Q

circular cam rings are

A

used in a vane pump that has variable displacement but are also unbalanced

52
Q

what is an advantage of a vane pump cartridge

A

can be quickly repaired by replacing the cartridge

53
Q

most multiple vane pump configurations have

A

a common inlet port that supplies oil to each pump

54
Q

a variable displacement pump that reduces its flow rate in relation to outlet oil pressure is called

A

pressure compensated pump

55
Q

what limits maximum flow rate of a variable displacement vane pump

A

maximum volume stop screw

56
Q

what holds the cam ring at maximum displacement on a variable displacement vane pump

A

compensator spring

57
Q

on a intra vane design outlet pressure acts on the vane at all quadrants

A

true

58
Q

what are three differences of a fixed vane pump vs a variable

A

cam ring is elliptical . there are two inlet ports opposite each other and two outlet ports opposite each other .

59
Q

when changing rotation of a fixed vane pump you must

A

rotate the cam ring 90 degrees

60
Q

how can you tell direction of rotation on a vane pump

A

direction of rotation is often indicated on the outside of the pump by an arrow cast into the housing

61
Q

tow designs of radial piston pumps

A

rotating piston . rotting cam

62
Q

in a radial rotating cam piston pump the pistons are

A

located in a fixed body and the center shaft has a cam that drives the piston out

63
Q

what prevents high pressure oil from entering the pumping chamber on a radial piston pump

A

check valve

64
Q

what makes a variable radial piston pump able to be variable

A

pressure builds inside acting against the spring force that normally holds it against the cam

65
Q

how dose a radial piston pump balance the piston in the cylinder

A

by allowing high pressure oil to act on the bottom of the piston shoe equalizing pressure and hydraulically balancing the piston

Hydralics (12 decks)

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