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3rd Year Millwright > Hydraulics > Flashcards

Hydraulics Flashcards

1
Q

define pressure

A

force on a unit of area

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2
Q

when pressure is applied to a fluid that is at rest and confined in a system, is this pressure distributed equally throughout all parts of the system or is it concentrated in some parts of the system?

A

distributed equally

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3
Q

why is pressure transmitted almost instantly through hydraulic fluid?

A

fluid is incompressible

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4
Q

what is meant by gauge pressure?

A

pressure measured on the gauge not including atmospheric pressure

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5
Q

why does a cylinder have a lower load capacity when it retracts than when it extends?

A

the annular area is smaller because the rod takes up surface space

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6
Q

how can you increase the force exerted by a cylinder of any given size?

A

increase the setting of the operating pressure

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7
Q

would you use a larger or a smaller cylinder if you needed to increase the load capacity of a given pressure?

A

larger

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8
Q

does a pump produce pressure, flow, or both?

A

flow

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9
Q

for a given flow create does a larger diameter cylinder or a small diameter cylinder move faster?

A

smaller

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10
Q

how fast does a 2:1 cylinder extend compared to how fast it retracts?

A

it extends half the speed it retracts

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11
Q

how does a reduction in pipe size affect pressure?

A

it decreases the pressure

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12
Q

how does a decrease in pipe size affect velocity?

A

it increases velocity

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13
Q

is a laminar or turbulent flow more effective for transmitting power?

A

laminar

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14
Q

when the velocity of a fluid increases does the pressure increase or decrease?

A

pressure decreases

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15
Q

what produces pressure?

A

resistance to flow

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16
Q

how does pressure affect the output of a cylinder?

A

it effects the force

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17
Q

how does flow affect the output of a cylinder?

A

it effects the speed

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18
Q

what are 3 negative effects of high fluid velocities in a hydraulic system?

A

wastes power
robs pressure
wears out components

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19
Q

define cavitation

A

violent collapse of entrained gas bubbles

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20
Q

what are 3 causes of cavitation?

A

clogged inlet filters
pump is mounted too high
too many bends or fittings

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21
Q

what is the basic cause of aeration?

A

when air gets inside fluid from an outside source

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22
Q

define work

A

force applied over a distance

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23
Q

define power

A

work over time

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24
Q

what is volumetric efficiency?

A

power out / power in - %

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25
Q

what causes a decrease in volumetric efficiency?

A

internal leakage

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26
Q

what is the main hazard to always be aware of when working on hydraulic systems?

A

high pressure

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27
Q

what hazard can exist after a hydraulic system has been locked out?

A

system can still be charged with high pressure fluid

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28
Q

what are the 5 main parts of a hydraulic system?

A

reservoir
conductors
pump
control valve
actuators

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29
Q

is a pressure reducing valve normally open or closed?

A

open

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30
Q

what is the purpose of a sequence valve?

A

to allow an actuator to operate to the end of a cycle before it allows another to operate

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31
Q

which valve would you use to prevent the uncontrolled fall of a load due to gravity?

A

counterbalance valve

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32
Q

why must you attach an external drain to a sequence valve or to a pressure reducing valve?

A

to prevent the valve from locking up under load

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33
Q

what is the purpose of a flow control?

A

to control the speed of an actuator

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34
Q

name 3 types of flow controls

A

meter in
meter out
bleed off

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35
Q

what term is used for the output component of a hydraulic system?

A

actuator

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36
Q

what 3 factors do the valves control in a hydraulic system?

A

direction
speed
force

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37
Q

what is an important reason for using electronic controls?

A

extreme accuracy

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38
Q

name 3 types of conductors used in hydraulics

A

pipes
hoses
tubes

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39
Q

what type of valve controls the speed of the actuator?

A

flow control valve

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40
Q

what type of valve controls the force of an actuator?

A

pressure control valve

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41
Q

which pressure control valves are usually closed?

A

relief
unloading
sequence
counterbalance
brake

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42
Q

which pressure control valve is normally open?

A

pressure reducing valve

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43
Q

which valve is the first valve downstream from the pump in a hydraulic system?

A

maximum pressure relief valve

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44
Q

what are 4 ways to unload a pump?

A

vent the relief
use an unloading relief
on/off valve
pilot operated unloading valve

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45
Q

what happens if you do not provide a pilot drain on a sequence valve or a pressure reducing valve?

A

it will not operate after a few cycles

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46
Q

what happens if you install a brake valve on a motor without connecting the pilot to the inlet?

A

the motor will not turn

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47
Q

what 3 types of elements are used in directional control valves?

A

sliding spool
rotary spool
poppet

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48
Q

what is it meant by a way in a valve?

A

passage for the main flow

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49
Q

what are 2 ways to use a three-way, two-position directional control valve?

A

used to operate a single cylinder
diverter

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50
Q

list two ways to use a three-way, two-position directional control valve

A

used to control a single cylinder
diverter

51
Q

what is the purpose of the pilot chokes on a directional control valve?

A

control the shift speed of the spool

52
Q

how are valves held in their normal positions?

A

by springs

53
Q

what types of spool centres would you use to allow the cylinder to flow?

A

open center
float center

54
Q

what is the main purpose of a maximum pressure relief valve?

A

to relieve the max pressure in case of an overload

55
Q

what is the purpose of an unloading valve?

A

used to depressurize a part of the system or whole system before the max pressure relief valve opens

56
Q

would you use a normally open or normally closed valve to relieve the pressure in a system?

A

normally closed

57
Q

what can happen if you set the max pressure relief valve about the maximum pressure for which the system is rated?

A

serious damage or injury

58
Q

what is pressure override?

A

difference between full flow pressure and cracking pressure

59
Q

what is the purpose of venting the relief valve?

A

to unload a system remote from the relief valve

60
Q

would you use a normally open or normally closed valve to reduce the pressure in a branch of a circuit?

A

normally open

61
Q

what happens if a particle of dirt gets caught between the poppet and dead of the reverse flow bypass on a pressure reducing valve?

A

you are not able to reduce the pressure

62
Q

would you use a normally open or normally closed valve to control the sequence of an operation?

A

normally closed

63
Q

if the second cylinder in a sequence circuit fails to move after the first cylinder completes its stroke, which troubleshooting technique should you try first?

A

adjust the spring to a lower pressure

64
Q

which pressure control valve can be used instead of a counterbalance valve?

A

a sequence valve

65
Q

should you connect the pilot from a brake valve to the inlet or the outlet of the motor?

A

brake valves have 2, one for the motor inlet and one for the outlet

66
Q

can you operate a double acting cylinder with a three-way, two-position directional control valve?

A

no

67
Q

which type of spool center do you need if the cylinder must be locked when the spool is in the center position and the pump flow is to circulate freely back to the tank without going over the relief?

A

tandem centre

68
Q

what happens if someone shuts off the pilot chokes?

A

the main spool will not shift

69
Q

how can you check to determine whether the pilot solenoids are working?

A

manually shift the pilot spool and see if the main spool moves

70
Q

what kind of spool do you need to increase the extension speed of a cylinder?

A

regenerative center

71
Q

what kind of check valve do you need if you want to have a minimum pressure loss in the valve?

A

right angle check valve

72
Q

what kind of check valve do you need to lock a double acting cylinder when the directional control valve spool is centred?

A

pilot to open

73
Q

what kind of check valve do you need to automatically drain an accumulator when the pump is shut down?

A

pilot to close

74
Q

does a flow control valve control the force or the speed of an actuator?

A

speed

75
Q

what is the safest flow control method (meter in or meter out) if the cylinder is used for a steady lift with the rod extending?

A

meter in

76
Q

which flow control method provides the best control when the loading is unsteady?

A

meter out

77
Q

where should you locate a flow control with a reverse flow bypass control the speed of the actuator in both directions?

A

upstream from the directional control valve

78
Q

what kind of flow control valve allows speed control in one direction and full speed in the other direction?

A

valves with reverse flow bypass

79
Q

what is the purpose of a pressure compensator on a flow control valve?

A

to ensure a steady flow when the load fluctuates

80
Q

what is the purpose of a temperature compensator on a flow control valve?

A

to maintain steady speed of an actuator with temperature changes

81
Q

what is the purpose of the over speed control feature on a flow control valve?

A

to prevent speed increase if directional control is suddenly shifted

82
Q

when you close down a flow control to reduce the flow from the pump to the actuator, where does the flow from the pump go that does not go to the actuator?

A

over the check valve back to the tank

83
Q

what is the purpose of using more than one stack of valves on a multiple station sub-plate?

A

to control more than one actuator

84
Q

what are 2 advantages of using a cartridge valve assembly?

A

compact
fewer leak points

85
Q

why is the area ratio of slip-in cartridge poppet important?

A

it determines the pressure the valve opens

86
Q

what is the spool movement proportional to in a proportional valve?

A

electrical input

87
Q

what is the purpose of the notches on proportional valve spool?

A

control flow

88
Q

what 6 devices provide input signals to the amplifier card for proportional valves?

A

potentiometers
temperature sensors
pressure transducers
tach generators
joystick
PIC

89
Q

what is the main reason for using a servo valve instead of a proportional valve?

A

greater accuracy

90
Q

what is the main maintenance concern with servo valves?

A

cleanliness

91
Q

what must you prevent when assembling stack valves?

A

make sure the o-rings are properly seated and the bolts are tightened evenly

92
Q

which stack valve must be placed at the top?

A

directional control

93
Q

which valve must be placed closest to the supply to the sub plate in a stack valve assembly?

A

relief valve

94
Q

which type of cartridge valve is used for low flows?

A

screw in type

95
Q

list 2 specifications that determine whether a slip in cartridge valve opens

A

area ratio on spool
available pressure at port

96
Q

if a screw in cartridge valve fails should you repair it or throw it out?

A

throw it out

97
Q

what is the difference between the operation of a conventional solenoid-controlled directional control valve and the operation of a proportional valve?

A

conventional - one way or the other
proportional - infinite ways

98
Q

which extra function can a proportional directional valve perform?

A

flow control

99
Q

list 3 ways a proportional valve is better than a servo valve:

A

more rugged
more dirt tolerant
less expensive

100
Q

besides speed, what else can a proportional valve control?

A

acceleration and deceleration

101
Q

which type of proportional valve spool is best for controlling a motor?

A

restricted centre spool

102
Q

what is the main function of an amplifier card?

A

increase the input signal to drive the solenoid

103
Q

list 4 functions that an amplifier card can provide besides increasing the power of a signal

A

dead band compensators
gain signal
dither signal
ramp settings

104
Q

what does the ramp setting control?

A

acceleration and deceleration

105
Q

what does the closed inner loop system control on a proportional valve in order to provide more accurate control of the actuator

A

the spool position

106
Q

which device does a proportional valve use to sense the spools position?

A

LVDT

107
Q

what does the summing junction in an amplifier do?

A

compares the actual position and set position of a spool or actuator and send the signal

108
Q

what does a closed outer loop system on a proportional valve correct?

A

actuator position

109
Q

what is the operating principal of proportional pressure controls?

A

solenoid replaces springs to set pressure

110
Q

list 3 types of proportional pressure controls

A

nozzle
plate
poppet

111
Q

which is more accurate a servo valve or a proportional valve?

A

servo

112
Q

list 3 types of servo valves

A

flapper
jet pipe
staged

113
Q

what does hysteresis indicate?

A

accuracy of the valve

114
Q

what is the purpose of keeping the lines from the valve to the actuator as short as possible on servo valves and proportional valves?

A

more accurate control

115
Q

pumps produce ________ in a hydraulic system.

A

flow

116
Q

what creates pressure in a hydraulic system?

A

resistance to flow

117
Q

what are the three groups of control valves found in hydraulic systems?

A

directional control
flow control
pressure control

118
Q

what does hydrostatic mean?

A

it’s a closed loop circuit.
charge pump that pumps fluid from motor back to inlet of pump.
no storage reservoir

119
Q

what component is always located directly after the pump in a hydraulic system?

A

maximum pressure relief valve

120
Q

what are the 5 main components of a hydraulic system?

A

reservoir
conductors
pump
control valve
actuator

121
Q

what is the main safety hazard when working with hydraulics?

A

high pressure hazard

122
Q

what are two advantages of hydraulic systems?

A

instant control
very compact

123
Q

what are the two disadvantages of hydraulic systems?

A

expensive
fire hazard

3rd Year Millwright (21 decks)

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