millwright level 3 > hydraulic pumps > Flashcards

hydraulic pumps Flashcards

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1
Q

what is the purpose of a pump in hydraulics

A

produce flow not pressure

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1
Q

why are non positive (dynamic) pumps not suitable to operate hydraulic systems?

A

their output changes with every change in system pressure

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1
Q

because the seal is positive the output is not affected by ?

A

back pressure

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2
Q

where’s the seal in a positive displacement pump

A

between the inlet and outlet

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3
Q

how much leakage is controlled leakage due to running clearances between the moving parts and due to the need for lubrication of these parts

A

5%-15%

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4
Q

types of postitive dispalcemnt pumps ?

A

piston
vane
gear

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4
Q

the amount of this internal leakage is typical of pumps in new condition when they are operated at their max rates pressure

A

5%-15%

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5
Q

how do you change the output of a hydraulic pump?

A

use a flow control and relief valve built into the discharge passage
change speed of drive

use a variable displacement pump

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6
Q

when doing pump maintenance you always want to fine the?

A

root cause

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7
Q

why is a piston pump sought after

A

reliable service over extended periods of life ,powerful output when compared to its size which is smaller than other pumps

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8
Q

piston pumps have piston that slide back and fourth inside cylinders true or false

A

true they retract to create larger volume to allow fluid to flow through their inlet ports they extend to push fluid out through discharge ports

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9
Q

what causes the swash plate to make the pistons reciprocate

A

the angle of the swash plate

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10
Q

types of piston pumps

A

in-line axial piston
bent axis piston
rotary piston
radial piston

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10
Q

what supports the pistons and allow them to slide on the surface of the swash plate

A

the shoes

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11
Q

true or false there are built in controls to vary the angle on the swash plate

A

true

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12
Q

how is the stroke adjusted ?

A

by changing the angle of the swash plate
no angle = no flow
small angle =small flow
large angle= large flow

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13
Q

the swash plate is supported by a yoke that ?

A

pivots and pintles are used to pivot the yoke

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14
Q

automatic swash plate controls are built into the pump 2 types are

A

presssure limitting compensator
load sensing compensator

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15
Q

LSHT
HSLT

A

low speed high torque
high speed low torque

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15
Q

features of LSHT motors ?

A

smooth operation under heavy loads
high starting and stall torque
start smoothly under full load
little torque variation through speed range

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15
Q

applications of lsht motors

A

crane hoists
dynamic rollers
power steering motor

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16
Q

features of HSLT motors

A

operate at high speeds
maintain high speeds under steady loads

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17
Q

applications of HSLT motors

A

fans
generators
compressors

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18
Q

what is starting torque

A

torque required to start the motor

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19
true or false if a motor has heavy parts and high friction it requires less starting torque to get turning
false requires more lots of torque
20
what is efficiency
ratio of work done or energy developed by a machine or engine
20
name 3 internal gear motors
direct drive orbiting gear motors roller van geroteres
21
the compensator moves the swash plate to an increased angle and allows the pistons to operate at a longer stroke , longer stoke produce more ?
torque and speed
22
where is a radial piston design used for
severe service it is a low speed high torque motor
23
what does a clicking sounds mean in a radial piston motor
inner surface of the valve housing is scored
23
name four piston motors
in-line axial piston bent axis radial piston cam type radial piston
24
radial piston motor should be at least 90% efficient a lower efficency means ?
worn rings on the pistons and or valve spool
25
What is the fit type of the assembly in an external gear motor?
Transition fit (close to zero clearance) ## Footnote This fit prevents rotation due to slight machining imperfections.
26
What should be ensured before starting an external gear motor?
The system is equipped with a return line filter ## Footnote A magnet in the return line or reservoir is also recommended.
27
What is the initial speed at which the external gear motor should be run during start-up?
Half speed ## Footnote Monitor the inlet and discharge flow rates during this phase.
28
During the initial run, what is the expected discharge flow rate compared to the inlet flow rate?
75% or 80% of the inlet flow ## Footnote This indicates the efficiency during the initial start-up phase.
29
What should be monitored while running the motor at half speed?
Inlet and discharge flow rates ## Footnote The motor runs hot at this stage.
30
What should be done once the motor starts to cool?
Continue running the motor until the discharge flow increases to at least 85% of the inlet flow ## Footnote This indicates that the casing has conformed to the gears.
31
What efficiency should be achieved when running the motor at full speed?
At least 85% ## Footnote Check the inlet and discharge flows at this stage.
32
What maintenance should be performed after the motor has been run?
Change the return line filter and clean the metal filings from the magnet ## Footnote This ensures continued efficiency and performance.
33
What are the three types of internal gear motors?
* Direct drive gear motors * Orbiting gear motors * Roller vane gerotors ## Footnote Each type has different operational characteristics.
34
What is the operating principle of any hydraulic motor?
Fluid pushes one pistons, vanes, gear teeth to rotate drive shaft
35
Which three (3) types of motors are used for low speed and high torque?
* Axial piston * Cam type axial piston * Roller vane gerotor
36
Which type of motor can only turn part of a rotation?
Limited Rotation motors
37
Which type of limited rotation motor can be used for clamping?
Cylinder with bell crank
38
Which three (3) specifications determine the torque in a motor?
* Inlet pressure * Surface area of motor elements * Means of rotation
39
What does a decrease in mechanical efficiency indicate?
Internal friction in the motor
40
What does a decrease in volumetric efficiency indicate?
Internal leakage
41
On which two (2) factors does motor speed depend?
* Flow rate - faster the flow, faster motor turns * Volume
42
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?
Gears and casing are fit too loosely
43
Why should you check the return line filter and magnet (if a magnet is used) after you have run a new or rebuilt motor for the first time?
Metal is removed from casing during bleeding
44
On which type of gear motor must you set the timing?
Orbiting gear motor
45
Should you be able to slide the rotor and rollers together easily on a roller vane gerotor or should they be very difficult to assemble?
Very difficult
46
What is the operating principle of any hydraulic motor?
Fluid pushes one pistons, vanes, gear teeth to rotate drive shaft
47
Which three (3) types of motors are used for low speed and high torque?
* Axial piston * Cam type axial piston * Roller vane gerotor
48
Which type of motor can only turn part of a rotation?
Limited Rotation motors
49
Which type of limited rotation motor can be used for clamping?
Cylinder with bell crank
50
Which three (3) specifications determine the torque in a motor?
* Inlet pressure * Surface area of motor elements * Means of rotation
51
What does a decrease in mechanical efficiency indicate?
Internal friction in the motor
52
What does a decrease in volumetric efficiency indicate?
Internal leakage
53
On which two (2) factors does motor speed depend?
* Flow rate - faster the flow, faster motor turns * Volume
54
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?
Gears and casing are fit too loosely
55
Why should you check the return line filter and magnet (if a magnet is used) after you have run a new or rebuilt motor for the first time?
Metal is removed from casing during bleeding
56
On which type of gear motor must you set the timing?
Orbiting gear motor
57
Should you be able to slide the rotor and rollers together easily on a roller vane gerotor or should they be very difficult to assemble?
Very difficult
58
59
60
61
What additional parts are found in vane motors that are not normally found in vane pumps?
Added springs under the vanes
62
List two (2) ways that the swash plate angle affects the performance of an in-line axial piston motor.
* Speed * Torque
63
When you change a valve assembly on a radial piston motor, why must you mark the position of the drive coupling on the motor and on the valve as soon as you remove the old valve?
To ensure valve is correctly timed
64
How can you change the displacement of a cam-type radial piston motor?
Change the cam ring to a different size
65
Which type of cylinder is used in a hydraulic jack?
ram
66
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
67
Why is it best to install a cylinder with the ports at the top?
Bleed out air
68
What two (2) things should you look for to be sure that you have received a motor and not a pump by mistake?
* Motor designation on nameplate * M prefix in model number
69
What happens if you try to start up a vane motor without the springs in it?
Fluid bypass vane tips, motor won't turn
70
What happens if you do not time a radial piston motor correctly?
It runs in reverse
71
If the supply is normal to a radial piston motor, but it runs slower than normal, what should you check first?
Condition of valve
72
What additional parts are found in vane motors that are not normally found in vane pumps?
Added springs under the vanes
73
List two (2) ways that the swash plate angle affects the performance of an in-line axial piston motor.
* Speed * Torque
74
When you change a valve assembly on a radial piston motor, why must you mark the position of the drive coupling on the motor and on the valve as soon as you remove the old valve?
To ensure valve is correctly timed
75
How can you change the displacement of a cam-type radial piston motor?
Change the cam ring to a different size
76
Which type of cylinder is used in a hydraulic jack?
r9m
77
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
78
Why is it best to install a cylinder with the ports at the top?
Bleed out air
79
What two (2) things should you look for to be sure that you have received a motor and not a pump by mistake?
* Motor designation on nameplate * M prefix in model number
80
What happens if you try to start up a vane motor without the springs in it?
Fluid bypass vane tips, motor won't turn
81
What happens if you do not time a radial piston motor correctly?
It runs in reverse
82
If the supply is normal to a radial piston motor, but it runs slower than normal, what should you check first?
Condition of valve
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