pump service and fundamentals questions Flashcards
hydraulic pumps that are able to change their pumping chambers are called
variable displacement pumps
a pump termed reversible is able to
reverse the direction of oil flow internally through the pump
as pump outlet pressure increases the pumps internal leakage decreases
false . as pump outlet pressure increases the pumps internal leakage also increases
why do manufacturers make gear pumps with aluminium housings allowing the gears to cut a gear path in the housing during break in
to provide good volumetric efficiency by keeping gear tip clearance to a minimum
what is the function of the trap in a gear pump pressure plate
the trap provides an escape path for oil trapped between the gear teeth to escape as they come into mesh
why is some internal leakage necessary with all hydraulic pumps
lubrication of moving parts
two reasons why oil pressure from the pumping chambers of an axial piston pump is connected to the piston shoes
to lubricate the ball socket between the piston and the shoe as well as the contact area between the shoe and the swash plate . also balancing the piston by offsetting the force generated by the pressure in the pumping chamber
the oil that gathers in the case of an axial piston pump comes from
internal leakage
three general guidelines to follow during pump disassembly
mark pump housing to return to original location . determine the direction of driveshaft rotation . be sure to keep mated components together and in original position
what is the most common cause of pitted erosion on the internal surface of a pump
cavitation
what are three reasons that could cause a pump to have lack of lubrication
improper oil for application . low oil reservoir level causing inlet to be uncovered . severe aeration
four tasks to be preformed when pump is changed
change oil change filters clean oil tank clean out lines
why should the adjustment of pressure controls be backed off prior to starting a machine after the hydraulic pump has been replaced
to prevent overloading of the pump in the event controls have been misadjusted prior to pump replacement
when the internal volume of a hydraulic pump increases the pressure
decreases
hydraulic oil is forced out of a pump when the volume of the pumping chamber is decreased true or false
true
pumps that have a constant pumping chamber are known as
fixed displacement
hydraulic pumps that are able to change the displacement of their pumping chambers are known as
variable displacement pumps
three categories of pump efficiency are
mechanical . volumetric . overall
as the pumps outlet pressure increases the pumps internal leakage decreases true or false
false . internal leakage will increase with pump outlet pressure
overall pump efficiency is
a comparison of pump input and output power
what are two factors that determine the amount of internal leakage in a pump
pressure difference between pump inlet and outlet pressure . amount of internal clearance within the pump
a unidirectional pump that is driven in the opposite direction it is intended to will
have the oil flow through the pump reversed
what are the main differences between the cam ring used in an unbalanced to a balanced vane pump design
the cam ring in an unbalanced uses a circular bore while the cam ring in a balanced design uses an elliptical design
pressure plates in vane pumps control
rotor side clearance
what are two forces acting on the vanes of a typical vane pump
centrifugal force and oil pressure acting on the underside of the vanes
why must the force exerted by the vanes acting on the cam ring in high performance pumps be reduced
to avoid the vane breaking the film of oil separating them from the cam ring . resulting in metal to metal contact
when an pressure limiting axial piston pump reaches maximum system pressure what will the swash plate do
it will move to a zero displacement position
a hydraulic control system that copies the movement of the control lever is called
a servo system
with the intra vane design what pressure is acting on the space in the slot above the intra vane
outlet oil pressure
in a rotating piston radial piston pump what force is holding the pistons against the cam ring inside the pump
centrifugal force
how can the rotating piston radial piston pump be made variable
by adjusting the relationship between the cylinder block and the cam ring thus changing the length of stroke
how can a radial cam piston pump be made variable
by sending outlet oil back into the pump housing acting on the pistons around the cam and limiting their stroke
formula to calculate flow rate of a pump
pump displacement x rpm then divided by 1000cm3
what is mechanical efficiency
an expression of how much power is required to overcome the internal friction of the pump
what is volumetric efficiency
the expression of how effective a pump can generate flow
how is volumetric efficiency calculated
by dividing actual flow rate of the pump by theoretical flow rate then x 100 to get a volumetric efficiency %
what is pump slip
a term that refers to the amount of oil leaking from outlet to inlet side of a pump
what ae two conditions that will allow slippage to increase in a hydraulic pump
the amount of wear a pump has and the amount of pressure difference from outlet to inlet
what is overall efficiency
comparing input power with the power delivered by the pump
what would cause a loss of overall efficiency at the max rage of operation in a hydraulic pump
increased internal leakage and higher mechanical losses due to internal loading
where dose overall efficiency peak in a hydraulic pump
at normal operation ranges
why must all hydraulic pumps be pre lubricated prior to pump start up
to ensure all moving parts have access to oil
where is the trap located on a pressure plate of a gear pump
on the outlet side of the pump and must be rotated 180 degrees if driveshaft rotation is reversed
what are the three types of gears available in a gear pump
spur . helical . herring bone
what are the most common type of gears used in a gear pump
non hunting spur cut gears
what is cavitation most commonly caused by
improper oil . restrictions in the inlet side . over speeding f the pump
