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3rd Year Millwright > Hydraulic Pumps & Actuators > Flashcards

Hydraulic Pumps & Actuators Flashcards

1
Q

do pumps create pressure or flow?

A

flow

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2
Q

why are positive displacement pumps used in hydraulics?

A

the output is not effected by back pressure

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3
Q

does the volume of the pumping chambers expand or contract at the inlet?

A

expand

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4
Q

what are 3 methods of changing the output of a pump?

A

flow control and build in relief
speed up the driver
use variable displacement pump

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5
Q

if a pump is mounted above the surface of the liquid, what provides the pressure to push the fluid up into the pump?

A

atmospheric pressure

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6
Q

what are 3 ways to push a fluid into a pump besides using atmospheric pressure?

A

gravity
pressurized reservoir
charge pump

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7
Q

how is the stroke increased on an axial piston pump?

A

increase the angle of the swash plate

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8
Q

which swash plate control limits the maximum pressure in a system?

A

pressure limiting compensator

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9
Q

which swash plate control regulates the flow to suit any given load?

A

load sensing compensator

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10
Q

what is the main reason for using the pressure limiting compensator and the load sensing compensator?

A

saved energy

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11
Q

what would happen if you set the load sensing compensator at 0 psi?

A

there wouldn’t be enough pressure to get a full stroke

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12
Q

what must you do to a new or rebuilt pump before you install it?

A

fill the case with fluid

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13
Q

how can you increase the stroke on a bent axis piston pump?

A

increase the cylinder block angle

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14
Q

which component of a rotary piston pump ports the fluid in and out of the cylinder?

A

pintle

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15
Q

how can you increase the flow from a rotary piston pump?

A

move the reaction ring away from the center

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16
Q

which part of a radial piston pump drives the piston?

A

an eccentric drive cam

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17
Q

how is the output flow increased on an unbalanced vane pump?

A

move the cam ring off center

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18
Q

what 2 methods are normally used to hold the vanes out against the cam ring on a vane pump?

A

centrifugal force
fluid pressure

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19
Q

which type of pump is more compact, the balanced vane pump or the unbalanced vane pump?

A

balanced

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20
Q

what is the rotation of a factory rebuilt balanced vane pump?

A

right hand

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21
Q

from which end of the pump is the direction of rotation defined?

A

drive end

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22
Q

how do you change the direction of rotation of a balanced vane pump?

A

flip the cam ring, rotor, and flex plate

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23
Q

what are 3 indications of contamination damage in a vane pump?

A

marks on the inside of the cam ring
frosted look to the vanes
circular marks on the flex plate

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24
Q

what are 2 indications of cavitation or aeration damage in a vane pump?

A

ripple marks on the inside of the cam ring
erosion at the ports

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25
Q

on a gear pump, do the teeth go into or come out of mesh at the inlet?

A

come out of mesh

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26
Q

what determines the volumetric efficiency of a gear pump?

A

the close fit between the gears

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27
Q

why do gear pumps require heavy needle bearings?

A

they are unbalanced and need to support a heavy radial load

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28
Q

is the crescent seal in an internal gear pump becomes worn, what happens to the flow inside the pump?

A

discharge flow will go back to the inlet

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29
Q

how can you change the output of a gear pump?

A

change the speed of the driver

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30
Q

what are 2 symptoms of wear from contamination in gear pumps?

A

scored ware plates
sharp teeth on gears

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31
Q

what can you do to repair a gear pump if only the ware plates are scored and the teeth are sharp?

A

replace the wear plates and fill the teeth

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32
Q

what is the maximum efficiency of new gear pump?

A

85%

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33
Q

what, if any, change should you expect in the output of a positive displacement pump as the back pressure increases?

A

small decrease

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34
Q

what, if any, change should you expect in the output of a positive displacement pump as the back pressure increase?

A

small decrease

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35
Q

why is it better to locate a pump below the level of the fluid than above the surface?

A

more pressure is available

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36
Q

what condition occurs when the inlet flow is less than the discharge?

A

cavitation

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37
Q

what are 3 methods of ensuring adequate inlet flow?

A

gravity
pressurized reservoir
charge pump

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38
Q

why is it worthwhile to examine a pump that you are about to replace?

A

to determine the cause of failure

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39
Q

how is the flow rate from an in-line axial piston pump increased?

A

increase the swash plate angle

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40
Q

what is the purpose of the bias piston in an in-line axial piston pump?

A

move the swash plate to the maximum angle

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41
Q

which is the best pump to use if you must locate it above the surface of the fluid, an in-line axial piston pump or a bent axis pump?

A

bent axis

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42
Q

how is the fluid ported in and out of a radial piston pump?

A

check valves in the pistons

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43
Q

does the space between the vanes and cam ring increase or decrease at the discharge of the pump?

A

decrease

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44
Q

how many inlet and discharge ports would you see in a balanced vane pump flex plate?

A

2 inlet and 2 discharge

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45
Q

what are 2 root causes of heat discolouration on a cam ring that you should check?

A

aeration
bad fluid

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46
Q

why is a very close fit necessary between the teeth and between the teeth and the casing on a gear pump?

A

to prevent flow back to the inlet

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47
Q

in an internal gear pump, should the inside gear have more or less teeth than the outer gear?

A

less

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48
Q

should you expect a new gear pump to be more or less efficient than a piston pump?

A

less

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49
Q

what is a double acting cylinder?

A

a cylinder that exerts force in both directions

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50
Q

which seals are contained in the rod bushing?

A

wiper seals
pressure seals

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51
Q

what is caused by failed rod seals?

A

dirt and air get into the system

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52
Q

which type of piston rings would you see if no creep can be tolerated?

A

synthetic

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53
Q

what are 2 reasons for using cast iron piston rings?

A

higher temperatures
higher pressures

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54
Q

under what operating conditions would you use cylinder cushions?

A

when the load could force the piston to hit the end of the cylinder

55
Q

when would you require a cushion bypass?

A

if the cylinder is loaded as it begins its stroke

56
Q

when would you need a stop tube?

A

when you have a long rod with side loads

57
Q

why is an ORB fitting preferred over a tapered thread fitting?

A

less stress and distortion

58
Q

should you normally install a cylinder with the ports at the top or the bottom?

A

the top

59
Q

why is it important to align a cylinder with the load to which it is attached?

A

to avoid wear on seals and cylinder walls

60
Q

what is the most costly result of leaks in a cylinder?

A

dirt and air get into the system and damage internal components

61
Q

how can you detect an internal leak in a cylinder?

A

hot spots

62
Q

what is the operating principal of any hydraulic motor?

A

fluid pushing on vanes, gears, or pistons to turn the drive shaft

63
Q

which 3 types of motors are used for low speed and high torque?

A

radial piston
cam-type radial piston
roller vane gerotor

64
Q

which type of motor can only turn part of a rotation?

A

limited rotation motor

65
Q

which type of limited rotation motor can be used for clamping

A

cylinder with bell crank

66
Q

which 3 specifications determine the torque in a motor?

A

inlet pressure
surface area
radius of rotation

67
Q

what does a decrease in mechanical efficiency indicate?

A

Internal friction

68
Q

what does a decrease in volumetric efficiency indicate?

A

Internal leakage

69
Q

What two factors does motor speed depend on?

A

displacement
flow speed

70
Q

If you rebuild a gear motor with new parts, and you find that it turns freely by hand, what is the problem with the motor?

A

The gears, and the casting are too loosely fitted

71
Q

why should you check the return line filter and magnet after you have run a new or rebuilt motor for the first time?

A

there could be metal shavings from the break-in

72
Q

On which type of gear motor must you set the timing?

A

orbiting gear motor

73
Q

should you be able to slide the rotor and rollers together easily on a roller vein gerotor or should they be very difficult to assemble?

A

Very difficult

74
Q

Which additional parts are found in vein motors that are not normally found in vein pumps?

A

Springs under the veins

75
Q

List two ways that the swash plate angle affects the performance of an in-line, axial piston motor

A

speed
torque

76
Q

when you change a valve assembly on a radial piston motor, why must you mark the piston of the drive coupling on the motor and on the valve as soon as you remove the old valve?

A

To make sure the timing is correct

77
Q

how can you change the displacement of a cam type radial piston motor?

A

Use a different sized cam ring

78
Q

which type of cylinder is used in a hydraulic jack?

A

ram

79
Q

what dangerous condition can develop if you shut off the cushion valve at the rod end of a cylinder that has a load pulling on it?

A

Pressure intensification

80
Q

Why is it best to install a cylinder with the ports at the top?

A

it allows you to bleed the air after assembly

81
Q

what two things should you look for to be sure that you received a motor and not a pump by mistake?

A

Motor designation on the plate
“M” prefix in the model number

82
Q

What happens if you try to start up a vein motor without the springs in it?

A

The motor will not run

83
Q

What happens if you do not time a radial piston motor correctly?

A

it runs in reverse

84
Q

If the supply is normal to a radial piston motor, but it runs slower than normal, what should you check first?

A

The valve condition

85
Q

how are the veins in an unbalanced main pump held against the cam ring?

A

centrifugal force
Hydraulic pressure

86
Q

What is the unbalanced vein pumps main disadvantage?

A

The casting and bearings must be fairly large to support the large radio forces

87
Q

How do you detect an internal leak in a cylinder?

A

Hotspots

88
Q

when would you need a cushion bypass?

A

If the cylinder is loaded at the beginning of its stroke

89
Q

What seals are found in a rod bushing?

A

Rod wiper seals
Pressure seals

90
Q

what type of piston motors commonly known as a staffa?

A

A radial piston motor

91
Q

What are the four types of piston motors?

A

in-line axial
bent axis
Radial piston
Cam type radial piston

92
Q

what is the difference in the design of a vein motor as opposed to a vein pump?

A

Vein motors have springs under the veins

93
Q

why must you time the gears with the rotary vein on an orbiting gerator motor

A

To make sure the vein ports the fluid to the correct area between gears

94
Q

What are the three types of internal gear motors?

A

Direct drive
Orbiting
Roller vane

95
Q

what is torque?

A

The rotational force of a motor

96
Q

What is displacement in terms of motor performance?

A

The amount of fluid required to turn the output shaft one rotation

The total volume of all the fluid in all the chambers in the motor

97
Q

What are the two kinds of piston type limited rotation motors?

A

piston and Bell crank
Rack and pinion

98
Q

What is a limited rotation motor?

A

A motor that has been modified to allow the motor to only turn part of a rotation

99
Q

where is dirt and air most commonly sucked into a cylinder

A

Worn rod seals

100
Q

What is the crush on an O-ring?

A

10%

101
Q

When would you use a stop tube?

A

When you have a long cylinder rod, that would magnify any sideload

102
Q

When would you use a cylinder cushion?

A

Applications were the load can force the piston to hit the end of the cylinder

103
Q

What type of a cylinder can push and pull simultaneously?

A

Double rod cylinder

104
Q

what is a differential cylinder?

A

A cylinder that has an unequal area on each side of the piston

105
Q

Is a gear pump more or less efficient than a piston pump?

A

Less

106
Q

how many inlet ports and discharge ports does a balanced vane pump have

A

To inlet and to discharge

107
Q

How is fluid moved in and out of a radial piston pump?

A

Check valves in the piston

108
Q

what does the biased piston do in an in-line axial piston pump?

A

It moves the swash plate angle to the maximum angle

109
Q

How do you move the reaction ring on a rotary piston pump

A

hand wheel
Pressure compensator

110
Q

How do you increase the stroke on a rotary piston pump?

A

Move the reaction ring away from the centre of the cylinder block

111
Q

how do you change the length of stroke in a bent axis piston pump?

A

Change the angle between the cylinder block and the driveshaft

112
Q

how can the output of an in-line axial piston pump be varied

A

By changing the length of it stroke

By changing the angle of the squash plate

113
Q

What two kinds of automatic wash plate controls can be built into a piston pump

A

pressure limiting compensator

Loadsensing compensator

114
Q

What are the four types of piston pumps?

A

in-line axial
Bent axis
Rotary
Radio

115
Q

How do you change the output of a hydraulic pump?

A

flow control, and relief valve built into the discharge passage

Change the speed of the driver

Use a variable displacement

116
Q

what are the three types of positive displacement pumps?

A

piston
vane
Gear

117
Q

What are the two classes of pumps?

A

non-positive displacement (dynamic)
Positive displacement

118
Q

do you use a positive displacement pump or a non-positive displacement pump for hydraulic systems?

A

Positive displacement

119
Q

Why do gear pumps require heavy needle bearings

A

They’re unbalanced and need to support heavy radial loads

120
Q

What part of a radial piston pump drives the pistons?

A

Eccentric drive cam

121
Q

What part of a rotary piston pump ports the fluid in and out of the cylinder?

A

pintle

122
Q

Why are positive displacement pumps used in hydraulics

A

The output is not affected by back pressure

123
Q

What is the maximum volumetric efficiency of a gear pump?

A

85%

124
Q

how do you change the output of a gerator internal gear pump?

A

Change the speed of the driver

125
Q

What is the tooth count of the inner gear compared to the outer gear on an internal gear pump?

A

The inner gear has at least one less tooth than the outer gear

126
Q

What is the crescent seal for on an internal gear pump?

A

It seals the inlet from the outlet

127
Q

What are the three designs on gears for external gear pumps?

A

spur

helical

Herringbone

128
Q

What gear design requires thrust bearings

A

helical

129
Q

what is the most common gear design used for external gear pumps?

A

Spur gears

130
Q

on an external gear pump, do the teeth come into mesh at the inlet or the outlet

A

The outlet

131
Q

What are the two main causes of vein pump failure?

A

contamination
Cavitation/aeration

132
Q

From which end do you view the pump from to determine the direction of rotation?

A

Drive end

133
Q

How do you change the direction of rotation on a balance pain pump?

A

Flip the camera and rotor over

134
Q

how do you change the fluid displacement on a balanced vane pump?

A

change the size of the cam ring

3rd Year Millwright (21 decks)

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