Pumps

Question 1

major types of pumps are

Answer 1

gear . vane . piston

Question 2

hydraulic pumps convert

Answer 2

mechanical energy to hydraulic

Question 3

how dose a pump convert energy

Answer 3

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

Question 4

what is the basic pumping principle

Answer 4

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

Question 5

pumps that have a constant pumping chamber volume will deliver

Answer 5

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

Question 6

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

Answer 6

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

Question 7

why is a internal gear pump a fixed displacement pump

Answer 7

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

Question 8

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

Answer 8

sum of the capacity of the vane pockets per revolution

the capacity cannot change therefor the displacement cannot change

Question 9

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

Answer 9

the sum of all the pumping chambers per revolution

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

Question 10

variable displacement pumps

Answer 10

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

Question 11

why can gear pumps not be variable in displacement

Answer 11

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

Question 12

how can vane pumps be variable displacement

Answer 12

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

Question 13

what are the three different designs of piston pumps

Answer 13

axial . bent axial and radial

Question 14

how do piston pumps have variable displacement

Answer 14

by changing the stroke length of the pistons

Question 15

axial piston pumps have

Answer 15

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

Question 16

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

Answer 16

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

Question 17

bent axial piston pumps have

Answer 17

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

Question 18

how do you change displacement on a bent axial piston pump

Answer 18

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

Question 19

how dose a reversible displacement pump change directions

Answer 19

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

Question 20

where would you most likely use a reversible displacement pump

Answer 20

as a hydrostatic transmission ( HST )

Question 21

what could result if maximum pump input speed is exceeded

Answer 21

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

Question 22

what will pump efficiency specifications tell you

Answer 22

how well the pump is converting mechanical energy to hydraulic energy

Question 23

what are the three categories of pump efficiency

Answer 23

mechanical . volumetric . overall

Question 24

mechanical efficiency is

Answer 24

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

Question 25

volumetric efficiency is

Answer 25

how effectively a hydraulic pump generates flow

Question 26

how do you calculate volumetric efficiency of a pump

Answer 26

by comparing theoretical and actual flow rate

Question 27

what do all hydraulic pumps have

Answer 27

internal leakage

Question 28

why is internal leakage important

Answer 28

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

Question 29

what is pump slip

Answer 29

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

Question 30

what two things contribute to pump slippage

Answer 30

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

Question 31

overall efficiency is

Answer 31

comparing input power with the power the pump will deliver

Question 32

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

Answer 32

increased internal leakage and higher mechanical losses caused by internal loading

Question 33

three advantages of an external gear pump

Answer 33

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

Question 34

two disadvantages of external gear pumps

Answer 34

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

Question 35

basic components of a external gear pump

Answer 35

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

Question 36

why are external gear pumps considered unbalanced pumps

Answer 36

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

Question 37

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

Answer 37

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

Question 38

what is a unidirectional pump

Answer 38

operates in only one direction

Question 39

what is the most identifiable feature of a bi directional pump

Answer 39

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

Question 40

advantages of a vane pump

Answer 40

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

Question 41

disadvantages of a vane pump

Answer 41

more expensive . more susceptible to contamination damage

Question 42

components of a three piece vane pump

Answer 42

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

Question 43

components of a two piece vane pump

Answer 43

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

Question 44

vane pump rotor

Answer 44

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

Question 45

vane pump vanes

Answer 45

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

Question 46

two common types of vane tips are

Answer 46

rounded and bevelled

Question 47

what two forces act on the vanes of a vane pump

Answer 47

outlet pressure and centrifugal force

Question 48

what benefits do a intra vane provide

Answer 48

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

Question 49

cam ring of a vane pump provides

Answer 49

the surface on witch the vanes run on

Question 50

elliptical cam rings are

Answer 50

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

Question 51

circular cam rings are

Answer 51

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

Question 52

what is an advantage of a vane pump cartridge

Answer 52

can be quickly repaired by replacing the cartridge

Question 53

most multiple vane pump configurations have

Answer 53

a common inlet port that supplies oil to each pump

Question 54

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

Answer 54

pressure compensated pump

Question 55

what limits maximum flow rate of a variable displacement vane pump

Answer 55

maximum volume stop screw

Question 56

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

Answer 56

compensator spring

Question 57

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

Answer 57

true

Question 58

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

Answer 58

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

Question 59

when changing rotation of a fixed vane pump you must

Answer 59

rotate the cam ring 90 degrees

Question 60

how can you tell direction of rotation on a vane pump

Answer 60

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

Question 61

tow designs of radial piston pumps

Answer 61

rotating piston . rotting cam

Question 62

in a radial rotating cam piston pump the pistons are

Answer 62

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

Question 63

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

Answer 63

check valve

Question 64

what makes a variable radial piston pump able to be variable

Answer 64

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

Question 65

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

Answer 65

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