Hydraulic Pumps & Actuators Flashcards
(134 cards)
1
Q
do pumps create pressure or flow?
A
flow
2
Q
why are positive displacement pumps used in hydraulics?
A
the output is not effected by back pressure
3
Q
does the volume of the pumping chambers expand or contract at the inlet?
A
expand
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
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
6
Q
what are 3 ways to push a fluid into a pump besides using atmospheric pressure?
A
gravity
pressurized reservoir
charge pump
7
Q
how is the stroke increased on an axial piston pump?
A
increase the angle of the swash plate
8
Q
which swash plate control limits the maximum pressure in a system?
A
pressure limiting compensator
9
Q
which swash plate control regulates the flow to suit any given load?
A
load sensing compensator
10
Q
what is the main reason for using the pressure limiting compensator and the load sensing compensator?
A
saved energy
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
12
Q
what must you do to a new or rebuilt pump before you install it?
A
fill the case with fluid
13
Q
how can you increase the stroke on a bent axis piston pump?
A
increase the cylinder block angle
14
Q
which component of a rotary piston pump ports the fluid in and out of the cylinder?
A
pintle
15
Q
how can you increase the flow from a rotary piston pump?
A
move the reaction ring away from the center
16
Q
which part of a radial piston pump drives the piston?
A
an eccentric drive cam
17
Q
how is the output flow increased on an unbalanced vane pump?
A
move the cam ring off center
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
19
Q
which type of pump is more compact, the balanced vane pump or the unbalanced vane pump?
A
balanced
20
Q
what is the rotation of a factory rebuilt balanced vane pump?
A
right hand
21
Q
from which end of the pump is the direction of rotation defined?
A
drive end
22
Q
how do you change the direction of rotation of a balanced vane pump?
A
flip the cam ring, rotor, and flex plate
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
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
25
on a gear pump, do the teeth go into or come out of mesh at the inlet?
come out of mesh
26
what determines the volumetric efficiency of a gear pump?
the close fit between the gears
27
why do gear pumps require heavy needle bearings?
they are unbalanced and need to support a heavy radial load
28
is the crescent seal in an internal gear pump becomes worn, what happens to the flow inside the pump?
discharge flow will go back to the inlet
29
how can you change the output of a gear pump?
change the speed of the driver
30
what are 2 symptoms of wear from contamination in gear pumps?
scored ware plates
sharp teeth on gears
31
what can you do to repair a gear pump if only the ware plates are scored and the teeth are sharp?
replace the wear plates and fill the teeth
32
what is the maximum efficiency of new gear pump?
85%
33
what, if any, change should you expect in the output of a positive displacement pump as the back pressure increases?
small decrease
34
what, if any, change should you expect in the output of a positive displacement pump as the back pressure increase?
small decrease
35
why is it better to locate a pump below the level of the fluid than above the surface?
more pressure is available
36
what condition occurs when the inlet flow is less than the discharge?
cavitation
37
what are 3 methods of ensuring adequate inlet flow?
gravity
pressurized reservoir
charge pump
38
why is it worthwhile to examine a pump that you are about to replace?
to determine the cause of failure
39
how is the flow rate from an in-line axial piston pump increased?
increase the swash plate angle
40
what is the purpose of the bias piston in an in-line axial piston pump?
move the swash plate to the maximum angle
41
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?
bent axis
42
how is the fluid ported in and out of a radial piston pump?
check valves in the pistons
43
does the space between the vanes and cam ring increase or decrease at the discharge of the pump?
decrease
44
how many inlet and discharge ports would you see in a balanced vane pump flex plate?
2 inlet and 2 discharge
45
what are 2 root causes of heat discolouration on a cam ring that you should check?
aeration
bad fluid
46
why is a very close fit necessary between the teeth and between the teeth and the casing on a gear pump?
to prevent flow back to the inlet
47
in an internal gear pump, should the inside gear have more or less teeth than the outer gear?
less
48
should you expect a new gear pump to be more or less efficient than a piston pump?
less
49
what is a double acting cylinder?
a cylinder that exerts force in both directions
50
which seals are contained in the rod bushing?
wiper seals
pressure seals
51
what is caused by failed rod seals?
dirt and air get into the system
52
which type of piston rings would you see if no creep can be tolerated?
synthetic
53
what are 2 reasons for using cast iron piston rings?
higher temperatures
higher pressures
54
under what operating conditions would you use cylinder cushions?
when the load could force the piston to hit the end of the cylinder
55
when would you require a cushion bypass?
if the cylinder is loaded as it begins its stroke
56
when would you need a stop tube?
when you have a long rod with side loads
57
why is an ORB fitting preferred over a tapered thread fitting?
less stress and distortion
58
should you normally install a cylinder with the ports at the top or the bottom?
the top
59
why is it important to align a cylinder with the load to which it is attached?
to avoid wear on seals and cylinder walls
60
what is the most costly result of leaks in a cylinder?
dirt and air get into the system and damage internal components
61
how can you detect an internal leak in a cylinder?
hot spots
62
what is the operating principal of any hydraulic motor?
fluid pushing on vanes, gears, or pistons to turn the drive shaft
63
which 3 types of motors are used for low speed and high torque?
radial piston
cam-type radial piston
roller vane gerotor
64
which type of motor can only turn part of a rotation?
limited rotation motor
65
which type of limited rotation motor can be used for clamping
cylinder with bell crank
66
which 3 specifications determine the torque in a motor?
inlet pressure
surface area
radius of rotation
67
what does a decrease in mechanical efficiency indicate?
Internal friction
68
what does a decrease in volumetric efficiency indicate?
Internal leakage
69
What two factors does motor speed depend on?
displacement
flow speed
70
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?
The gears, and the casting are too loosely fitted
71
why should you check the return line filter and magnet after you have run a new or rebuilt motor for the first time?
there could be metal shavings from the break-in
72
On which type of gear motor must you set the timing?
orbiting gear motor
73
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?
Very difficult
74
Which additional parts are found in vein motors that are not normally found in vein pumps?
Springs under the veins
75
List two ways that the swash plate angle affects the performance of an in-line, axial piston motor
speed
torque
76
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?
To make sure the timing is correct
77
how can you change the displacement of a cam type radial piston motor?
Use a different sized cam ring
78
which type of cylinder is used in a hydraulic jack?
ram
79
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?
Pressure intensification
80
Why is it best to install a cylinder with the ports at the top?
it allows you to bleed the air after assembly
81
what two things should you look for to be sure that you received a motor and not a pump by mistake?
Motor designation on the plate
“M” prefix in the model number
82
What happens if you try to start up a vein motor without the springs in it?
The motor will not run
83
What happens if you do not time a radial piston motor correctly?
it runs in reverse
84
If the supply is normal to a radial piston motor, but it runs slower than normal, what should you check first?
The valve condition
85
how are the veins in an unbalanced main pump held against the cam ring?
centrifugal force
Hydraulic pressure
86
What is the unbalanced vein pumps main disadvantage?
The casting and bearings must be fairly large to support the large radio forces
87
How do you detect an internal leak in a cylinder?
Hotspots
88
when would you need a cushion bypass?
If the cylinder is loaded at the beginning of its stroke
89
What seals are found in a rod bushing?
Rod wiper seals
Pressure seals
90
what type of piston motors commonly known as a staffa?
A radial piston motor
91
What are the four types of piston motors?
in-line axial
bent axis
Radial piston
Cam type radial piston
92
what is the difference in the design of a vein motor as opposed to a vein pump?
Vein motors have springs under the veins
93
why must you time the gears with the rotary vein on an orbiting gerator motor
To make sure the vein ports the fluid to the correct area between gears
94
What are the three types of internal gear motors?
Direct drive
Orbiting
Roller vane
95
what is torque?
The rotational force of a motor
96
What is displacement in terms of motor performance?
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
What are the two kinds of piston type limited rotation motors?
piston and Bell crank
Rack and pinion
98
What is a limited rotation motor?
A motor that has been modified to allow the motor to only turn part of a rotation
99
where is dirt and air most commonly sucked into a cylinder
Worn rod seals
100
What is the crush on an O-ring?
10%
101
When would you use a stop tube?
When you have a long cylinder rod, that would magnify any sideload
102
When would you use a cylinder cushion?
Applications were the load can force the piston to hit the end of the cylinder
103
What type of a cylinder can push and pull simultaneously?
Double rod cylinder
104
what is a differential cylinder?
A cylinder that has an unequal area on each side of the piston
105
Is a gear pump more or less efficient than a piston pump?
Less
106
how many inlet ports and discharge ports does a balanced vane pump have
To inlet and to discharge
107
How is fluid moved in and out of a radial piston pump?
Check valves in the piston
108
what does the biased piston do in an in-line axial piston pump?
It moves the swash plate angle to the maximum angle
109
How do you move the reaction ring on a rotary piston pump
hand wheel
Pressure compensator
110
How do you increase the stroke on a rotary piston pump?
Move the reaction ring away from the centre of the cylinder block
111
how do you change the length of stroke in a bent axis piston pump?
Change the angle between the cylinder block and the driveshaft
112
how can the output of an in-line axial piston pump be varied
By changing the length of it stroke
By changing the angle of the squash plate
113
What two kinds of automatic wash plate controls can be built into a piston pump
pressure limiting compensator
Loadsensing compensator
114
What are the four types of piston pumps?
in-line axial
Bent axis
Rotary
Radio
115
How do you change the output of a hydraulic pump?
flow control, and relief valve built into the discharge passage
Change the speed of the driver
Use a variable displacement
116
what are the three types of positive displacement pumps?
piston
vane
Gear
117
What are the two classes of pumps?
non-positive displacement (dynamic)
Positive displacement
118
do you use a positive displacement pump or a non-positive displacement pump for hydraulic systems?
Positive displacement
119
Why do gear pumps require heavy needle bearings
They’re unbalanced and need to support heavy radial loads
120
What part of a radial piston pump drives the pistons?
Eccentric drive cam
121
What part of a rotary piston pump ports the fluid in and out of the cylinder?
pintle
122
Why are positive displacement pumps used in hydraulics
The output is not affected by back pressure
123
What is the maximum volumetric efficiency of a gear pump?
85%
124
how do you change the output of a gerator internal gear pump?
Change the speed of the driver
125
What is the tooth count of the inner gear compared to the outer gear on an internal gear pump?
The inner gear has at least one less tooth than the outer gear
126
What is the crescent seal for on an internal gear pump?
It seals the inlet from the outlet
127
What are the three designs on gears for external gear pumps?
spur
helical
Herringbone
128
What gear design requires thrust bearings
helical
129
what is the most common gear design used for external gear pumps?
Spur gears
130
on an external gear pump, do the teeth come into mesh at the inlet or the outlet
The outlet
131
What are the two main causes of vein pump failure?
contamination
Cavitation/aeration
132
From which end do you view the pump from to determine the direction of rotation?
Drive end
133
How do you change the direction of rotation on a balance pain pump?
Flip the camera and rotor over
134
how do you change the fluid displacement on a balanced vane pump?
change the size of the cam ring
