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50 Cards in this Set
- Front
- Back
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Do pumps create pressure or flow |
Flow |
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Why are positive displacement pumps used for hydraulics |
Accurate flow control is possible because flow is not affected by backpressure |
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Does the volume of the pumping chambers expand or contract at the inlet |
Expands |
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List three methods of changing the output of a pump |
Built in flow control and relief Drive speed change Variable displacement |
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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 |
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What are three ways to push fluid into a pump besides using atmospheric pressure |
Gravity Pressurized reservoir Charge pump |
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How is the stroke increased on an axial piston pump |
By increasing the swash plate angle |
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Which swash plate control limits the maximum pressure in the system |
Pressure limiting compensator |
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Which swash plate control regulates the flow to suit any given load? |
Load sensing compensator |
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what is the main reason for using the pressure limiting compensator and the load sensing compensator |
To save energy |
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What would happen if you set the load sensing compensator at zero psi |
There would be no pressure to operate the bias piston and bring the pump back to full stroke |
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what must you do to a new or rebuilt pump before you install it |
Fill the case with fluid |
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How can you increase the stroke on a bent axis piston pump |
Increase the cylinder block angle to the shaft axis |
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Which component of a rotary piston pump ports the fluid in and out of the cylinders |
Pintle |
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How can you increase the flow from a rotary piston pump? |
Move the reaction ring farther off center |
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Which part of a radial piston pump drives the pistons? |
An eccentric drive cam |
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Does the space between the vanes increase or decrease at the inlet |
Increases |
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How is the output flow increased on an unbalanced vane pump |
By moving the cam ring farther off center |
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What two methods are normally used to hold the vanes out against the cam ring on a vane pump |
Centrifugal force Fluid pressure under the vanes |
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Which type of pump is more compact, the balanced vane or the unbalanced vane pump |
Balanced vane |
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What is the rotation of a factory rebuilt balanced vane pump |
Right hand |
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From which end of the pump is the direction of rotation defined |
Drive end |
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How do you change the direction of rotation in a balanced vane pump |
Flip over the cam ring, rotor and flex plate assembly |
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Name three indications of contamination damage in a vane pump |
Marks around the inside of the cam ring Frosted appearance on the vanes Circular marks on the flex plates |
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Name two indications of cavitation or aeration damage in a vane pump |
Ripple marks inside the cam ring Erosion at the ports |
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On a gear pump, do the teeth go into or come out of mesh at the inlet |
Come out of mesh |
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What determines the volumetric efficiency of a gear pump |
The close fit between the gears and between the gears and the casing and wear plates |
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Why do gear pumps require heavy needle bearings |
Because they are hydraulically unbalanced, the bearings must support high radial loads |
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If the crescent seal in an internal gear pump becomes worn, what happens to the flow inside the pump |
Some of the discharge flow recirculates to the inlet |
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How can you change the output of a gear pump |
By changing the speed of the driver |
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Name two symptoms of wear contamination in gear pumps |
Wear plates scored Sharp edges on the tips of gear teeth |
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What can you do to repair a gear pump if only the wear plates are scored and the tips of the teeth have sharp edges |
Change the wear plates and stone off the sharp edges |
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What is the maximum efficiency that you can expect from a new gear pump |
85% |
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What is the basic operating principle of any positive displacement pump |
Pumping chambers increase in volume at the inlet and then decrease as they push the fluid out the discharge ports |
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What, if any, change should you expect in the output of a positive displacement pump as the back pressure increases |
Small decrease |
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Why is it better to locate a pump below the level of the fluid than above the surface |
More pressure is available to ensure adequate inlet flow |
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What condition occurs when the inlet flow is less than the discharge |
Cavitation |
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List three methods of ensuring adequate inlet flow |
Gravity Pressurized reservoir Charge pump |
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Why is it worthwhile to examine a pump that you are about to replace |
To determine the root cause of failure |
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How is the flow rate from an in-line axial piston pump increased |
By increasing the swash plate angle |
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What is the purpose of the bias piston in an in-line axial piston pump? |
To move the swash plate to the maximum angle |
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Which is the best pump to use if you have to locate it above the surface of the fluid: an in-line axial piston pump or a bent axis pump? |
Bent axis |
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How is the fluid ported in and out of a radial piston pump |
Through check valves in the pistons |
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Does the space between the vanes and the cam ring increase or decrease at the discharge port in a vane pump |
Decreases |
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How many inlet ports and how many discharge ports would you see in a balanced vane pump flex plate |
Two inlet and two discharge |
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Which direction of rotation are factory rebuilt or new balanced vane pumps assembled for? |
Right hand |
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List two root causes of heat discolouration on a cam ring that you should check |
Aeration Poor quality fluid |
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Why is a very close fit necessary between the teeth and between the teeth and the casing on a gear pump |
To prevent bypassing back to the inlet |
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On an internal gear pump, should the inside gear have the same number of teeth as the outside gear or should it have fewer teeth |
Fewer teeth |
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Should you expect a new gear pump to be more efficient or less efficient than a piston pump |
Less efficient |
