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hydraulics Flashcards

1
Q

What’s a hydraulic

A

Hydraulic is a means of transmitting power by pushing on a confined liquid

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2
Q

What does a pressure relief valve does

A

Protects the system components from excess pressure

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3
Q

Weight of oil creates how much pressure for every foot

A

0.4 psi or 0.03bar or 3kpa

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4
Q

What’s the formula of pressure

A

P=f/a

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5
Q

What’s heavier water or oil

A

Water

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6
Q

How much is atmospheric pressure at see level

A

14.7 psi or 1bar or 100 kpa

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7
Q

What’s the purpose of a pump

A

To create flow

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8
Q

Pressure is caused by

A

Resistance

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9
Q

Resistance comes from

A

1 from the load on the actuator
2 from an orifice or restriction in the piping

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10
Q

what is pascals law

A

pressure applied in confined fluid at rest .force is transmitted in every direction at right angle of to the container

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11
Q

how much does a hydraulic fluid compress

A

half percent at 1000 psi

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12
Q

what’s the formula of force

A

force =p times area

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13
Q

what kind of oil is best for a hydraulic oil

A

petroleum and synthetic

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14
Q

what’s is the meaning of hydro and aulos

A

its means water and pipe

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15
Q

formula of velocity

A

v = speed times area

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16
Q

main cause of frication in hydraulic line

A

excessive length of line
excessive velocity {line to small}
excessive number of bends

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16
Q

what is a meter in circuit

A

flow of oil is controlled at the INLET of actuator
oil that is going IN to the actuator is metered

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17
Q

what is meter out circuit

A

flow of oil is controlled at the OUTLET of actuator
oil that is going OUT to the actuator is metered

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18
Q

what is a bleed off circuit

A

flow of oil is controlled in the bypass line of actuator .leading to the tank

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19
Q

is a gear pump fixed or variable capacity / hydraulic pump

A

fixed capacity hydraulic pump
has 2 gear to create hydraulic pressure

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20
Q

what are examples of internal gear pumps

A

cresent pump
gerotor pump

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21
Q

what are examples of external gear pumps

A

gear pump

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22
Q

Does a shape of a vessel affect pascal law

A

No .shape doesn’t affect pascals law

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23
Q

does liquid expand or retract when heated

A

expand

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24
Q

what abbreviation is used in USA for pressure

A

psi

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25
Q

whats the relation of travel speed of samll piston to a bigger piston

A

small piston will travel faster

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26
Q

what term is used to denote the pressure developed by the weight of a liquid column

A

head pressure or hydrostatic pressure

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27
Q

what is the relation of the diameter of tank to the psi gauge pressure developed at the bottom of the tank

A

diameter doesn’t have effect only Hight affect the pressure

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28
Q

how is the force of a ram type cylinder figured

A

f =p times A

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28
Q

what cause fluid pressure to be developed in a column of fluid

A

gravity

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28
Q

what velocity ,in feet per sec is used to rate most hydraulic valves

A

15-20 psi

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29
Q

if a fluid in a pipe is not moving but under high pressure , does a small orifice inserted in the pipe have effect on the pressure

A

no effect

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30
Q

what is main advantage of telescoping cylinder ?

A

extends longer and very collapsible ?

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31
Q

the arrow on body of cheak valve points towards the free flow or direction of checked flow

A

points to the direction free flow

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32
Q

sampling hydrolic fluid is used determine

A

to see if there is a change in viscosty
and to find an excessive contamination

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33
Q

3 important funcation of oil reservoir in a hydrolic power system

A

to avoid straving the pump
cools oil
acts as a fluid conditioner

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34
Q

what should a reservoir capacity should be

A

2 or 3 times the pumps out put

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35
Q

a ———–is put in most reservoirs to separate pump intake from return oil discharge

A

baffle plate

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36
Q

what is the mesh size or micron rating of the of the pump intake strainer usually used for standard hydraulic oil ?

A

149 micron

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37
Q

four major function of fluid in a hydraulic system

A

cools
lubricate
seals

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38
Q

viscosity is a measure of a hydraulic fluid ————

A

resistance to flow

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39
Q

a hydraulic fluid with low viscosity flows faster or slower than a high viscosity oil ?

A

faster

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40
Q

an increase of internal leaking in system components may be an indication of ————–due to temperature ,

A

low viscosity

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41
Q

as liquid is cooled ,its internal resistance to flow ———

A

increase

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42
Q

a typical reservoir is divided in to 2 by a————–

A

baffle plate

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43
Q

the suction line intake is placed well below fluid level to prevent

A

airation

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44
Q

pressure must be ———–before replacing the element in a filter

A

released

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45
Q

in depth type fiteration ,contaminates of different ———are caught at different ———-of filtering element

A

size—————-stages

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46
Q
A

Strainer

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47
Q
A

Fixed displacement unidirectional pump

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48
Q

What’s the does this symbol means ?

A

Unloading valve
Case thank
Normally closed
Down stream

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49
Q

Explain the details of this valve

A

4 way 3 port solenoid activated spring centred , open center dcv

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50
Q
A

Differential double acting cylinder

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51
Q
A

Unidirectional fixed displacement pump

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52
Q
A

Pressure relief valve

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53
Q
A

Pressure reducing valve .
Is always normally open

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54
Q
A

Bidirectional fixed displacement pressure compensated pump

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55
Q
A

Pressure relief valve

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56
Q
A

Trotting / proportioning / infinite valve

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57
Q
A

Cam activated
2 positions 2 way
normally open
case drained
spring return

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58
Q
A

Pressure compensated flow control

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59
Q
A

Pressure and temperature compensted flow control valve

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60
Q
A

Cheak valve piloted to open

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61
Q
A

Cheak valve piloted to close

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62
Q
A

Double acting with double end rod

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63
Q
A

Double acting tandem cylinder

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64
Q
A

Double acting duplex cylinder

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65
Q
A

Sequence valve because
It Is normal closed
up stream
Has a case tank

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66
Q
A

Counter balance valve

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67
Q

Is this diagram metered in or out / bleed off or regenerative ?

A

Metered in

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68
Q

Is this diagram metered in or out / bleed off or regenerative ?

A

Bleed off

69
Q

Is this diagram metered in or out / bleed off or regenerative ?

A

Regenerative

70
Q

Is this diagram metered in or out / bleed off or regenerative ?

A

Meter out

71
Q

What’s is a regenerative circuit

A

Cylinder extends by taking oil from rod end to head end .

72
Q

What is this symbol

A

Pressure switch

73
Q

What’s is the center and what will a cylinder with this center can do ?

A

Is an closed center and we are able to stop cylinder mid way

74
Q

What’s is the center position called?
What will a cylinder do in this position?

A

Is an open center.
Cylinder will slowly creep up because head end has more surface area than the rod end

75
Q

What is the center position called and
What will the cylinder do in this position?

A

It is tandem center .
Cylinder can hold its position at any point .

76
Q

What’s is this symbol ?

A

It is a gas charged accumulator

77
Q

What’s is this symbol ?

A

Weighted accumulator

78
Q

What’s is this symbol ?

A

Heat exchanger

79
Q

What’s is this symbol ?

A

Heat exchanger with with liquid

80
Q

What’s is this symbol ?

A

Heater with fluid

81
Q

What’s is this symbol ?

A

Cooler

82
Q

What’s is this symbol ?

A

Heat exchanger with using gas

83
Q

What’s the formula of work

A

Work = force times distance

84
Q

What’s the common rpm of vain pump

A

600 rpm

85
Q

Is a piston pump fixed or variable?

A

It could be both

86
Q

Where do we usually use a brake valve .

A

Used in a rottary system

87
Q

1 bar is = ……………psi

A

1000 psi

88
Q

What shuld we consider when choosing seal for a hydrolic system?

A

Compatibility

89
Q

Shuld a cylinder shaft have textures?

A

Yes . For oil to lubricant seal

90
Q

Lip seal seals against high/ low pressure?

A

Low pressure (10 -15 psi

91
Q

Shuld a lip seal leak ?

A

Yes to lub shaft

92
Q

What’s the working pressure of a u cup seal ?

A

250 psi

93
Q

Where do we usually use a u cup seal ?

A

In pneumatic systems.

94
Q

Does a u cup seal high or low pressure?

A

Low pressure

95
Q

Where do we usually use a v cup ?

A

In a hydrolic system

96
Q

Does a v cup seal high or low pressure?

A

High pressure

97
Q

What seal is usually used in set?

A

V packing or chevron seal

98
Q

Does a v packing or chevron seal against high or low pressure?

A

High pressure. The more seals used the higher the pressure the seal

99
Q

Is O ring a static or dynamic seal?

A

Can be both

100
Q

O rings can seal up to ………..psi ?

A

1500 psi

101
Q

O rings can be used with a back up to seal against………………psi

A

3000 psi

102
Q

What’s the clearance of valve spool .

A

1/2 taw-2 taw

103
Q

What is usually use to install poly pack?

A

Heat.

104
Q

What’s the benefit of poly pack seal

A

Provide a high pressure sealing and longer wear

105
Q

Where do we usually find a metal rings .

A

In a heavy duty hydraulic system

106
Q

Metal rings seal are made from ?

A

Cast iron
Steel
Chrome plated

107
Q

What does a pilot operated dcv Mean ?

A

Means we use power or pressure to move the spool in the valve .

108
Q

What do pump creat ?

A

Flow

109
Q

How is pressure created?

A

By the resistance of flow

110
Q

What are the causes of cavitations

A

Pump to high
Inlet restriction
Inlet line to big or to small
High fluid viscosity
Pump over speed
Clogged breather

111
Q

What are the causes of aeration

A

Leaky inlet fitting
Reservoir vortexes
Leaky pump shaft seal

112
Q

Cavitation?

A

Liquid will vaporize in a vacuum and these bubbles, once carried through the pump, collapse (implode) with considerable force when exposed to load pressure at the outlet

113
Q

What does positive displacement mean With hydraulics?

A

Whatever gets into the pump is forced out of the outlet port

114
Q

________ ________ some other pressure eliminating device should be used in all systems using positive displacement pump?

A

Relief valve

115
Q

What is an orifice?

A

A restricted passage in a hydraulic line or component, used to control flow or create a pressure difference (pressure drop).

116
Q

With the orifice, what does pressure drop mean?

A

Pressure drop is the difference in pressure between the gauges up and downstream of the restriction (TRIANGLE w/ a P).

a. An increase in pressure drop across an orifice will always be accompanied by an increase in flow

117
Q

Force or torque of an actuator is directly proportional to the?

A

Pressure - it’s independent of the flow

118
Q

A gauge that reads with atmospheric pressure is designated as?

A

psia - called an absolute gauge

119
Q

With hydraulics, speed depend on?

A

Amount of fluid flow without regard to pressure

120
Q

With regards to velocity and pipes, what are the recommended ranges in pump inlet line and working lines?

A

a. Pump inlet lines = two - four feet per second

b. working lines = 7 to 20 feet per second

121
Q

What is the work and power formulas?

A

a. Work = force X distance

b. Power = work / time

121
Q

What is the horsepower (wattage) formula?

A

Hp = GPM x psi x .0007

122
Q

What is a hydrodynamic device?

A

It is a hydraulic device which uses the impact or kinetic energy in the liquid to transmit power

123
Q

Where does pressure head come from?

A

The weight of the fluid - the term head is used to describe pressure no matter how it is created.

124
Q

Any condition where pressure is less than atmospheric pressure is called a?

A

Vacuum or partial vacuum

125
Q

How do you convert PSIA to PSIG?

A

a. Absolute pressure = gauge pressure + 14.7

b. Gauge pressure = absolute pressure - 14.7

126
Q

What are the two ways to measure the flow of a fluid?

A

i. large volumes = GPM

ii. small volumes = cubic inches per minute

127
Q

What is laminar flow?

A

Particles of a fluid move through a pipe, they will move in a straight, parallel flow path. Occurs at low velocity and straight piping - friction is minimized

128
Q

What is turbulence? What causes it?

A

Condition where the particles do not move smoothly parallel to the flow direction - Caused by abrupt changes in direction, cross section, or by to high velocity.

129
Q

Hydraulic fluid and the working system contains energy in two forms?

A

a. Kinetic energy by virtue of the fluids weight and velocity

b. Potential energy in the form of pressure

130
Q

What is the Bernoulli theory?

A
  1. A system with a constant flow rate, energy is transformed from one form to the other each time the pipe cross section size changes

a. If kinetic energy decreases it results in an increase in the pressure energy.

131
Q

With hydraulic symbols, what is a working line? How was it shown on a diagram?

A

Working line carries the mainstream of flow in the system (pump inlet line, pressure lines and return lines to tank) - solid line

132
Q

With hydraulic symbols , what is the pilot or sensing line? How is it shown on a diagram?

A

Long dashes - carries fluid that is used to control the operation of valve or other component

133
Q

What are the use for fluid in hydraulic systems?

A

a. Cooling
b. Lubrication
c. Power Transmission (Foremost)
d. Sealing
e. Contaminant Removal

133
Q

With hydraulic symbols, what is the drain line? How is it shown on a diagram?

A

Short dashes - carries leakage oil back to the reservoir to prevent a pressure buildup in the area being drained.

134
Q

What is boundary lubrication?

A

Clearances between moving surfaces have been reduced by manufacturers to reduce leakage at higher pressure drops across clearances.

a. This can cause galling of the component services which creates work hardened metal wear contamination and severe heat

135
Q

What happens when the viscosity of oil is too high?

A

a. High resistance to flow

b. increased energy consumption

c. high temperatures created by power loss to friction

d. increased pressure drops due to resistance to flow

e. Slow or sluggish operation

f. Insufficient separation of air from the oil in the reservoir

g. Pump cavitation

136
Q

What happens when the viscosity of oil is too low?

A

a. Increased internal leakage
b. Excess wear
c. Decreased pump efficiency
d. Internal leakage

137
Q

Absolute viscosity?

A

Resistance encountered when moving one layer of liquid over another.

138
Q

What is Fluid conductors?

A
  1. Means to transport fluid from one point to another in a hydraulic circuit.

Three types:
a. Hose
b. steel tubing - designated by the outside diameter
c. pipe - low cost

139
Q

How is hose size designated?

A

By a dash number, which refers to the inside diameter in sixteenths of an inch (- 6 = 6/16” = 3/8”)

140
Q

What are the four types of typical hose ends (fittings)?

A

a. Crimp fitting
b. reusable fitting
c. JIC 37 connection
d. split flange connection

141
Q

Why is turbulent flow undesirable terroristic and what is the major contributor?

A

it Causes unnecessary friction within the fluid and against the conductors walls. Excessive fluid velocity is the major contributor to turbulence.

141
Q

What type of connectors does steel tubing have?

A

a. Flared type
b. Compression fitting type
c. Brazed or welded

142
Q

How much will the velocity of fluid increase if the conductor is reduced to half its original size?

A

It will increase by 4x

143
Q

What are the four common domestic port connections?

A

a. National pipe tapered fuel (NPTF)

b. SAE O-ring boss (ORB)

c. split flange - commonly used in fluid power systems at the pump inlet and on hydrostatic systems

d. JIC 37 or 45 degree
e. SAE flat face O-ring seal - offers the best in leakage control

144
Q

What are the five common guidelines that should always be followed when using O rings?

A

a. Use only O rings that are made of the material and proper durometer for the application

b. Ensure the o-ring is properly seated

c. O-ring should be lubricated

d. Keep all connecting surfaces clean
e. Never reuse an o-ring

145
Q

Where is the O ring seal used extensively?

A

It is used extensively to seal cylinder Pistons, piston rods, and other reciprocating parts

146
Q

What type of seal is a lip seal and where is it used?

A

Low pressure dynamic seals used principally to seal rotating shafts - They are a positive seal

147
Q

What type of seal is a cup seal and where is it used?

A

it is a positive seal used on many cylinder Pistons - it is pressure actuated in both directions (handle high pressure)

148
Q

What are the functions of reservoirs?

A

a. Holding the system fluid supply
b. Acts as a heat exchanger that cools the fluid
c. Allows entrained air to rise and escape
d. Solid contaminants settle to the bottom of the tank; fluid conditioner

149
Q

What are the standard reservoir tank designs?

A

a. JIC reservoirs
b. L-shaped reservoirs
c. Overhead stack reservoirs

150
Q

What factors should be considered when determining reservoir size?

A

a. Fluid expansion caused by high temperatures
b. Changes in fluid level due to system operation
c. Exposure of the tank interior to excess condensation
d. The amount of heat generated in the system

151
Q

What are the advantages to a vertically mounted reservoir assembly tank?

A

a. Reduced floor space
b. Increased cooling
c. Hydraulic fluid acts as an vibration dampener and noise suppressor
d. Reservoir fluid creates a pressure head surrounding the pump and it’s fitting eliminating the possibility of cavitation and aeration
e. Drive force stresses are reduced as a result of gravitational forces (side loading)
f. Hydraulic pump system is maintained cleaner in a sealed reservoir

152
Q

The size of the reservoir should be at least ______% over capacity to provide a reservoir against unexpected demands on system capacity?

A

20%

153
Q

What are the three types of heat exchangers?

A

a. Heaters
b. Air coolers
c. Water coolers

154
Q

What are the three source Categories of contamination in hydraulic systems?

A

a. Built in contamination - new equipment usually contains some built in contamination

b. ingressed contamination - contamination material that is added to the hydraulic system during service or maintenance

c. internally generated contamination - created within the system by moving parts
i. Particles grinding between moving surfaces
ii. metal of metal contact
iii. high velocity particles striking surfaces
iv. repeated stressing on a surface
v. high pump inlet vacuum
vi. gas bubbles in fluid
vii. Foreign substance and fluid

155
Q

What is abrasion?

A

Solid particles in the hydraulic fluid grinding between moving surfaces

a. One body - contamination damages a surface through contact
b. two body - contamination is embedded in surface making contact with another surface
c. three body - loose particles making contact with two surfaces

156
Q

what is erosion?

A

High velocity particles. Similar to abrasion

157
Q

What is adhesion?

A

metal to metal contact

158
Q

What is fatigue?

A

repeated stress of a surface

159
Q

what is cavitation?

A

Pressure reduction causes vapor filled cavities to form in the fluid. When the fluid is then pressurized these cavities will collapse causing severe shock and heat damage to the metal surfaces

160
Q

What is aeration?

A

Presence of air or gas bubbles in the fluid.

160
Q

What causes cavitation?

A

Exceeding recommended pump inlet vacuum, which can be caused by:

a. over speeding the pump
b. restricting inlet lines or air breathers
c. plugged inlet strainers
d. high viscosity oil

161
Q

what is silting?

A

Accumulation of very fine particulate contamination

162
Q

What are the three types of particulate contamination induced failures?

A

a. Catastrophic - rapid or sudden total disabling of a component or system
b. Intermittent - are transitory in occurrence and are most often self correcting
c. Degradation - translates to surface wear (where, corrosion, cavitation, aeration and erosion)

163
Q

What does an increase in case drain flow usually indicate?

A

The component is in a failure mode and has begun shedding particles that can ultimately cause catastrophic failures

164
Q

____________ ____________ maybe the single most important area in which the technician can directly contribute to operating efficiency and improved performance?

A

Contamination control

165
Q

What are the three range cleanliness code for a sample determined by (range code for contamination)?

A

a. 4 microns and above
b. 6 microns and above
c. 14 microns and above

166
Q

What are the three areas in hydraulic systems for locating A contamination controlled device?

A

a. Pressure line (pump outlet line)
b. return line
c. off loop type filtration/filling circuit

167
Q

In the inlet line between the reservoir and the pump, what size of microns will be caught in the mesh?

A

It is usually a 100 mesh screen that will trap particles larger than about 150 micrometers

168
Q

What type of pump should be used when a pressure compensated system is on standby for long periods of time?

A

Offline circulating pump

169
Q
A

Hydraulics (4 decks)

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