hydraulics Flashcards
(176 cards)
1
Q
What’s a hydraulic
A
Hydraulic is a means of transmitting power by pushing on a confined liquid
2
Q
What does a pressure relief valve does
A
Protects the system components from excess pressure
3
Q
Weight of oil creates how much pressure for every foot
A
0.4 psi or 0.03bar or 3kpa
4
Q
What’s the formula of pressure
A
P=f/a
5
Q
What’s heavier water or oil
A
Water
6
Q
How much is atmospheric pressure at see level
A
14.7 psi or 1bar or 100 kpa
7
Q
What’s the purpose of a pump
A
To create flow
8
Q
Pressure is caused by
A
Resistance
9
Q
Resistance comes from
A
1 from the load on the actuator
2 from an orifice or restriction in the piping
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
11
Q
how much does a hydraulic fluid compress
A
half percent at 1000 psi
12
Q
what’s the formula of force
A
force =p times area
13
Q
what kind of oil is best for a hydraulic oil
A
petroleum and synthetic
14
Q
what’s is the meaning of hydro and aulos
A
its means water and pipe
15
Q
formula of velocity
A
v = speed times area
16
Q
main cause of frication in hydraulic line
A
excessive length of line
excessive velocity {line to small}
excessive number of bends
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
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
18
Q
what is a bleed off circuit
A
flow of oil is controlled in the bypass line of actuator .leading to the tank
19
Q
is a gear pump fixed or variable capacity / hydraulic pump
A
fixed capacity hydraulic pump
has 2 gear to create hydraulic pressure
20
Q
what are examples of internal gear pumps
A
cresent pump
gerotor pump
21
Q
what are examples of external gear pumps
A
gear pump
22
Q
Does a shape of a vessel affect pascal law
A
No .shape doesn’t affect pascals law
23
Q
does liquid expand or retract when heated
A
expand
24
what abbreviation is used in USA for pressure
psi
25
whats the relation of travel speed of samll piston to a bigger piston
small piston will travel faster
26
what term is used to denote the pressure developed by the weight of a liquid column
head pressure or hydrostatic pressure
27
what is the relation of the diameter of tank to the psi gauge pressure developed at the bottom of the tank
diameter doesn't have effect only Hight affect the pressure
28
how is the force of a ram type cylinder figured
f =p times A
28
what cause fluid pressure to be developed in a column of fluid
gravity
28
what velocity ,in feet per sec is used to rate most hydraulic valves
15-20 psi
29
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
no effect
30
what is main advantage of telescoping cylinder ?
extends longer and very collapsible ?
31
the arrow on body of cheak valve points towards the free flow or direction of checked flow
points to the direction free flow
32
sampling hydrolic fluid is used determine
to see if there is a change in viscosty
and to find an excessive contamination
33
3 important funcation of oil reservoir in a hydrolic power system
to avoid straving the pump
cools oil
acts as a fluid conditioner
34
what should a reservoir capacity should be
2 or 3 times the pumps out put
35
a -----------is put in most reservoirs to separate pump intake from return oil discharge
baffle plate
36
what is the mesh size or micron rating of the of the pump intake strainer usually used for standard hydraulic oil ?
149 micron
37
four major function of fluid in a hydraulic system
cools
lubricate
seals
38
viscosity is a measure of a hydraulic fluid ------------
resistance to flow
39
a hydraulic fluid with low viscosity flows faster or slower than a high viscosity oil ?
faster
40
an increase of internal leaking in system components may be an indication of --------------due to temperature ,
low viscosity
41
as liquid is cooled ,its internal resistance to flow ---------
increase
42
a typical reservoir is divided in to 2 by a--------------
baffle plate
43
the suction line intake is placed well below fluid level to prevent
airation
44
pressure must be -----------before replacing the element in a filter
released
45
in depth type fiteration ,contaminates of different ---------are caught at different ----------of filtering element
size----------------stages
46
Strainer
47
Fixed displacement unidirectional pump
48
What’s the does this symbol means ?
Unloading valve
Case thank
Normally closed
Down stream
49
Explain the details of this valve
4 way 3 port solenoid activated spring centred , open center dcv
50
Differential double acting cylinder
51
Unidirectional fixed displacement pump
52
Pressure relief valve
53
Pressure reducing valve .
Is always normally open
54
Bidirectional fixed displacement pressure compensated pump
55
Pressure relief valve
56
Trotting / proportioning / infinite valve
57
Cam activated
2 positions 2 way
normally open
case drained
spring return
58
Pressure compensated flow control
59
Pressure and temperature compensted flow control valve
60
Cheak valve piloted to open
61
Cheak valve piloted to close
62
Double acting with double end rod
63
Double acting tandem cylinder
64
Double acting duplex cylinder
65
Sequence valve because
It Is normal closed
up stream
Has a case tank
66
Counter balance valve
67
Is this diagram metered in or out / bleed off or regenerative ?
Metered in
68
Is this diagram metered in or out / bleed off or regenerative ?
Bleed off
69
Is this diagram metered in or out / bleed off or regenerative ?
Regenerative
70
Is this diagram metered in or out / bleed off or regenerative ?
Meter out
71
What’s is a regenerative circuit
Cylinder extends by taking oil from rod end to head end .
72
What is this symbol
Pressure switch
73
What’s is the center and what will a cylinder with this center can do ?
Is an closed center and we are able to stop cylinder mid way
74
What’s is the center position called?
What will a cylinder do in this position?
Is an open center.
Cylinder will slowly creep up because head end has more surface area than the rod end
75
What is the center position called and
What will the cylinder do in this position?
It is tandem center .
Cylinder can hold its position at any point .
76
What’s is this symbol ?
It is a gas charged accumulator
77
What’s is this symbol ?
Weighted accumulator
78
What’s is this symbol ?
Heat exchanger
79
What’s is this symbol ?
Heat exchanger with with liquid
80
What’s is this symbol ?
Heater with fluid
81
What’s is this symbol ?
Cooler
82
What’s is this symbol ?
Heat exchanger with using gas
83
What’s the formula of work
Work = force times distance
84
What’s the common rpm of vain pump
600 rpm
85
Is a piston pump fixed or variable?
It could be both
86
Where do we usually use a brake valve .
Used in a rottary system
87
1 bar is = ……………psi
1000 psi
88
What shuld we consider when choosing seal for a hydrolic system?
Compatibility
89
Shuld a cylinder shaft have textures?
Yes . For oil to lubricant seal
90
Lip seal seals against high/ low pressure?
Low pressure (10 -15 psi
91
Shuld a lip seal leak ?
Yes to lub shaft
92
What’s the working pressure of a u cup seal ?
250 psi
93
Where do we usually use a u cup seal ?
In pneumatic systems.
94
Does a u cup seal high or low pressure?
Low pressure
95
Where do we usually use a v cup ?
In a hydrolic system
96
Does a v cup seal high or low pressure?
High pressure
97
What seal is usually used in set?
V packing or chevron seal
98
Does a v packing or chevron seal against high or low pressure?
High pressure. The more seals used the higher the pressure the seal
99
Is O ring a static or dynamic seal?
Can be both
100
O rings can seal up to ………..psi ?
1500 psi
101
O rings can be used with a back up to seal against………………psi
3000 psi
102
What’s the clearance of valve spool .
1/2 taw-2 taw
103
What is usually use to install poly pack?
Heat.
104
What’s the benefit of poly pack seal
Provide a high pressure sealing and longer wear
105
Where do we usually find a metal rings .
In a heavy duty hydraulic system
106
Metal rings seal are made from ?
Cast iron
Steel
Chrome plated
107
What does a pilot operated dcv Mean ?
Means we use power or pressure to move the spool in the valve .
108
What do pump creat ?
Flow
109
How is pressure created?
By the resistance of flow
110
What are the causes of cavitations
Pump to high
Inlet restriction
Inlet line to big or to small
High fluid viscosity
Pump over speed
Clogged breather
111
What are the causes of aeration
Leaky inlet fitting
Reservoir vortexes
Leaky pump shaft seal
112
Cavitation?
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
What does positive displacement mean With hydraulics?
Whatever gets into the pump is forced out of the outlet port
114
________ ________ some other pressure eliminating device should be used in all systems using positive displacement pump?
Relief valve
115
What is an orifice?
A restricted passage in a hydraulic line or component, used to control flow or create a pressure difference (pressure drop).
116
With the orifice, what does pressure drop mean?
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
Force or torque of an actuator is directly proportional to the?
Pressure - it's independent of the flow
118
A gauge that reads with atmospheric pressure is designated as?
psia - called an absolute gauge
119
With hydraulics, speed depend on?
Amount of fluid flow without regard to pressure
120
With regards to velocity and pipes, what are the recommended ranges in pump inlet line and working lines?
a. Pump inlet lines = two - four feet per second
b. working lines = 7 to 20 feet per second
121
What is the work and power formulas?
a. Work = force X distance
b. Power = work / time
121
What is the horsepower (wattage) formula?
Hp = GPM x psi x .0007
122
What is a hydrodynamic device?
It is a hydraulic device which uses the impact or kinetic energy in the liquid to transmit power
123
Where does pressure head come from?
The weight of the fluid - the term head is used to describe pressure no matter how it is created.
124
Any condition where pressure is less than atmospheric pressure is called a?
Vacuum or partial vacuum
125
How do you convert PSIA to PSIG?
a. Absolute pressure = gauge pressure + 14.7
b. Gauge pressure = absolute pressure - 14.7
126
What are the two ways to measure the flow of a fluid?
i. large volumes = GPM
ii. small volumes = cubic inches per minute
127
What is laminar flow?
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
What is turbulence? What causes it?
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
Hydraulic fluid and the working system contains energy in two forms?
a. Kinetic energy by virtue of the fluids weight and velocity
b. Potential energy in the form of pressure
130
What is the Bernoulli theory?
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
With hydraulic symbols, what is a working line? How was it shown on a diagram?
Working line carries the mainstream of flow in the system (pump inlet line, pressure lines and return lines to tank) - solid line
132
With hydraulic symbols , what is the pilot or sensing line? How is it shown on a diagram?
Long dashes - carries fluid that is used to control the operation of valve or other component
133
What are the use for fluid in hydraulic systems?
a. Cooling
b. Lubrication
c. Power Transmission (Foremost)
d. Sealing
e. Contaminant Removal
133
With hydraulic symbols, what is the drain line? How is it shown on a diagram?
Short dashes - carries leakage oil back to the reservoir to prevent a pressure buildup in the area being drained.
134
What is boundary lubrication?
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
What happens when the viscosity of oil is too high?
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
What happens when the viscosity of oil is too low?
a. Increased internal leakage
b. Excess wear
c. Decreased pump efficiency
d. Internal leakage
137
Absolute viscosity?
Resistance encountered when moving one layer of liquid over another.
138
What is Fluid conductors?
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
How is hose size designated?
By a dash number, which refers to the inside diameter in sixteenths of an inch (- 6 = 6/16" = 3/8")
140
What are the four types of typical hose ends (fittings)?
a. Crimp fitting
b. reusable fitting
c. JIC 37 connection
d. split flange connection
141
Why is turbulent flow undesirable terroristic and what is the major contributor?
it Causes unnecessary friction within the fluid and against the conductors walls. Excessive fluid velocity is the major contributor to turbulence.
141
What type of connectors does steel tubing have?
a. Flared type
b. Compression fitting type
c. Brazed or welded
142
How much will the velocity of fluid increase if the conductor is reduced to half its original size?
It will increase by 4x
143
What are the four common domestic port connections?
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
What are the five common guidelines that should always be followed when using O rings?
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
Where is the O ring seal used extensively?
It is used extensively to seal cylinder Pistons, piston rods, and other reciprocating parts
146
What type of seal is a lip seal and where is it used?
Low pressure dynamic seals used principally to seal rotating shafts - They are a positive seal
147
What type of seal is a cup seal and where is it used?
it is a positive seal used on many cylinder Pistons - it is pressure actuated in both directions (handle high pressure)
148
What are the functions of reservoirs?
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
What are the standard reservoir tank designs?
a. JIC reservoirs
b. L-shaped reservoirs
c. Overhead stack reservoirs
150
What factors should be considered when determining reservoir size?
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
What are the advantages to a vertically mounted reservoir assembly tank?
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
The size of the reservoir should be at least ______% over capacity to provide a reservoir against unexpected demands on system capacity?
20%
153
What are the three types of heat exchangers?
a. Heaters
b. Air coolers
c. Water coolers
154
What are the three source Categories of contamination in hydraulic systems?
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
What is abrasion?
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
what is erosion?
High velocity particles. Similar to abrasion
157
What is adhesion?
metal to metal contact
158
What is fatigue?
repeated stress of a surface
159
what is cavitation?
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
What is aeration?
Presence of air or gas bubbles in the fluid.
160
What causes cavitation?
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
what is silting?
Accumulation of very fine particulate contamination
162
What are the three types of particulate contamination induced failures?
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
What does an increase in case drain flow usually indicate?
The component is in a failure mode and has begun shedding particles that can ultimately cause catastrophic failures
164
____________ ____________ maybe the single most important area in which the technician can directly contribute to operating efficiency and improved performance?
Contamination control
165
What are the three range cleanliness code for a sample determined by (range code for contamination)?
a. 4 microns and above
b. 6 microns and above
c. 14 microns and above
166
What are the three areas in hydraulic systems for locating A contamination controlled device?
a. Pressure line (pump outlet line)
b. return line
c. off loop type filtration/filling circuit
167
In the inlet line between the reservoir and the pump, what size of microns will be caught in the mesh?
It is usually a 100 mesh screen that will trap particles larger than about 150 micrometers
168
What type of pump should be used when a pressure compensated system is on standby for long periods of time?
Offline circulating pump
169
