Hydraulic Pumps & Actuators Flashcards
do pumps create pressure or flow?
flow
why are positive displacement pumps used in hydraulics?
the output is not effected by back pressure
does the volume of the pumping chambers expand or contract at the inlet?
expand
what are 3 methods of changing the output of a pump?
flow control and build in relief
speed up the driver
use variable displacement pump
if a pump is mounted above the surface of the liquid, what provides the pressure to push the fluid up into the pump?
atmospheric pressure
what are 3 ways to push a fluid into a pump besides using atmospheric pressure?
gravity
pressurized reservoir
charge pump
how is the stroke increased on an axial piston pump?
increase the angle of the swash plate
which swash plate control limits the maximum pressure in a system?
pressure limiting compensator
which swash plate control regulates the flow to suit any given load?
load sensing compensator
what is the main reason for using the pressure limiting compensator and the load sensing compensator?
saved energy
what would happen if you set the load sensing compensator at 0 psi?
there wouldn’t be enough pressure to get a full stroke
what must you do to a new or rebuilt pump before you install it?
fill the case with fluid
how can you increase the stroke on a bent axis piston pump?
increase the cylinder block angle
which component of a rotary piston pump ports the fluid in and out of the cylinder?
pintle
how can you increase the flow from a rotary piston pump?
move the reaction ring away from the center
which part of a radial piston pump drives the piston?
an eccentric drive cam
how is the output flow increased on an unbalanced vane pump?
move the cam ring off center
what 2 methods are normally used to hold the vanes out against the cam ring on a vane pump?
centrifugal force
fluid pressure
which type of pump is more compact, the balanced vane pump or the unbalanced vane pump?
balanced
what is the rotation of a factory rebuilt balanced vane pump?
right hand
from which end of the pump is the direction of rotation defined?
drive end
how do you change the direction of rotation of a balanced vane pump?
flip the cam ring, rotor, and flex plate
what are 3 indications of contamination damage in a vane pump?
marks on the inside of the cam ring
frosted look to the vanes
circular marks on the flex plate
what are 2 indications of cavitation or aeration damage in a vane pump?
ripple marks on the inside of the cam ring
erosion at the ports
on a gear pump, do the teeth go into or come out of mesh at the inlet?
come out of mesh
what determines the volumetric efficiency of a gear pump?
the close fit between the gears
why do gear pumps require heavy needle bearings?
they are unbalanced and need to support a heavy radial load
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
how can you change the output of a gear pump?
change the speed of the driver
what are 2 symptoms of wear from contamination in gear pumps?
scored ware plates
sharp teeth on gears
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
what is the maximum efficiency of new gear pump?
85%
what, if any, change should you expect in the output of a positive displacement pump as the back pressure increases?
small decrease
what, if any, change should you expect in the output of a positive displacement pump as the back pressure increase?
small decrease
why is it better to locate a pump below the level of the fluid than above the surface?
more pressure is available
what condition occurs when the inlet flow is less than the discharge?
cavitation
what are 3 methods of ensuring adequate inlet flow?
gravity
pressurized reservoir
charge pump
why is it worthwhile to examine a pump that you are about to replace?
to determine the cause of failure
how is the flow rate from an in-line axial piston pump increased?
increase the swash plate angle
what is the purpose of the bias piston in an in-line axial piston pump?
move the swash plate to the maximum angle
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
how is the fluid ported in and out of a radial piston pump?
check valves in the pistons
does the space between the vanes and cam ring increase or decrease at the discharge of the pump?
decrease
how many inlet and discharge ports would you see in a balanced vane pump flex plate?
2 inlet and 2 discharge
what are 2 root causes of heat discolouration on a cam ring that you should check?
aeration
bad fluid
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
in an internal gear pump, should the inside gear have more or less teeth than the outer gear?
less
should you expect a new gear pump to be more or less efficient than a piston pump?
less
what is a double acting cylinder?
a cylinder that exerts force in both directions
which seals are contained in the rod bushing?
wiper seals
pressure seals
what is caused by failed rod seals?
dirt and air get into the system
which type of piston rings would you see if no creep can be tolerated?
synthetic
what are 2 reasons for using cast iron piston rings?
higher temperatures
higher pressures
under what operating conditions would you use cylinder cushions?
when the load could force the piston to hit the end of the cylinder
when would you require a cushion bypass?
if the cylinder is loaded as it begins its stroke
when would you need a stop tube?
when you have a long rod with side loads
why is an ORB fitting preferred over a tapered thread fitting?
less stress and distortion
should you normally install a cylinder with the ports at the top or the bottom?
the top
why is it important to align a cylinder with the load to which it is attached?
to avoid wear on seals and cylinder walls
what is the most costly result of leaks in a cylinder?
dirt and air get into the system and damage internal components
how can you detect an internal leak in a cylinder?
hot spots
what is the operating principal of any hydraulic motor?
fluid pushing on vanes, gears, or pistons to turn the drive shaft
which 3 types of motors are used for low speed and high torque?
radial piston
cam-type radial piston
roller vane gerotor
which type of motor can only turn part of a rotation?
limited rotation motor
which type of limited rotation motor can be used for clamping
cylinder with bell crank
which 3 specifications determine the torque in a motor?
inlet pressure
surface area
radius of rotation
what does a decrease in mechanical efficiency indicate?
Internal friction
what does a decrease in volumetric efficiency indicate?
Internal leakage
What two factors does motor speed depend on?
displacement
flow speed
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
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
On which type of gear motor must you set the timing?
orbiting gear motor
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
Which additional parts are found in vein motors that are not normally found in vein pumps?
Springs under the veins
List two ways that the swash plate angle affects the performance of an in-line, axial piston motor
speed
torque
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
how can you change the displacement of a cam type radial piston motor?
Use a different sized cam ring
which type of cylinder is used in a hydraulic jack?
ram
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
Why is it best to install a cylinder with the ports at the top?
it allows you to bleed the air after assembly
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
What happens if you try to start up a vein motor without the springs in it?
The motor will not run
What happens if you do not time a radial piston motor correctly?
it runs in reverse
If the supply is normal to a radial piston motor, but it runs slower than normal, what should you check first?
The valve condition
how are the veins in an unbalanced main pump held against the cam ring?
centrifugal force
Hydraulic pressure
What is the unbalanced vein pumps main disadvantage?
The casting and bearings must be fairly large to support the large radio forces
How do you detect an internal leak in a cylinder?
Hotspots
when would you need a cushion bypass?
If the cylinder is loaded at the beginning of its stroke
What seals are found in a rod bushing?
Rod wiper seals
Pressure seals
what type of piston motors commonly known as a staffa?
A radial piston motor
What are the four types of piston motors?
in-line axial
bent axis
Radial piston
Cam type radial piston
what is the difference in the design of a vein motor as opposed to a vein pump?
Vein motors have springs under the veins
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
What are the three types of internal gear motors?
Direct drive
Orbiting
Roller vane
what is torque?
The rotational force of a motor
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
What are the two kinds of piston type limited rotation motors?
piston and Bell crank
Rack and pinion
What is a limited rotation motor?
A motor that has been modified to allow the motor to only turn part of a rotation
where is dirt and air most commonly sucked into a cylinder
Worn rod seals
What is the crush on an O-ring?
10%
When would you use a stop tube?
When you have a long cylinder rod, that would magnify any sideload
When would you use a cylinder cushion?
Applications were the load can force the piston to hit the end of the cylinder
What type of a cylinder can push and pull simultaneously?
Double rod cylinder
what is a differential cylinder?
A cylinder that has an unequal area on each side of the piston
Is a gear pump more or less efficient than a piston pump?
Less
how many inlet ports and discharge ports does a balanced vane pump have
To inlet and to discharge
How is fluid moved in and out of a radial piston pump?
Check valves in the piston
what does the biased piston do in an in-line axial piston pump?
It moves the swash plate angle to the maximum angle
How do you move the reaction ring on a rotary piston pump
hand wheel
Pressure compensator
How do you increase the stroke on a rotary piston pump?
Move the reaction ring away from the centre of the cylinder block
how do you change the length of stroke in a bent axis piston pump?
Change the angle between the cylinder block and the driveshaft
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
What two kinds of automatic wash plate controls can be built into a piston pump
pressure limiting compensator
Loadsensing compensator
What are the four types of piston pumps?
in-line axial
Bent axis
Rotary
Radio
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
what are the three types of positive displacement pumps?
piston
vane
Gear
What are the two classes of pumps?
non-positive displacement (dynamic)
Positive displacement
do you use a positive displacement pump or a non-positive displacement pump for hydraulic systems?
Positive displacement
Why do gear pumps require heavy needle bearings
They’re unbalanced and need to support heavy radial loads
What part of a radial piston pump drives the pistons?
Eccentric drive cam
What part of a rotary piston pump ports the fluid in and out of the cylinder?
pintle
Why are positive displacement pumps used in hydraulics
The output is not affected by back pressure
What is the maximum volumetric efficiency of a gear pump?
85%
how do you change the output of a gerator internal gear pump?
Change the speed of the driver
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
What is the crescent seal for on an internal gear pump?
It seals the inlet from the outlet
What are the three designs on gears for external gear pumps?
spur
helical
Herringbone
What gear design requires thrust bearings
helical
what is the most common gear design used for external gear pumps?
Spur gears
on an external gear pump, do the teeth come into mesh at the inlet or the outlet
The outlet
What are the two main causes of vein pump failure?
contamination
Cavitation/aeration
From which end do you view the pump from to determine the direction of rotation?
Drive end
How do you change the direction of rotation on a balance pain pump?
Flip the camera and rotor over
how do you change the fluid displacement on a balanced vane pump?
change the size of the cam ring
