Pumps Flashcards
major types of pumps are
gear . vane . piston
hydraulic pumps convert
mechanical energy to hydraulic
how dose a pump convert energy
by taking energy from a prime mover and generating flow through a system
what is the basic pumping principle
increasing the internal volume during the intake cycle creates a low pressure that allows atmospheric head pressure to push oil into the pumps inlet
pumps that have a constant pumping chamber volume will deliver
the same amount of fluid with every revolution with a constant input rpm
on a gear pump the volume of oil delivered in one revolution will be the sum of capacities of
all the gear tooth pockets on both the driven and drive gears
why is a internal gear pump a fixed displacement pump
because the capacity of each gear tooth cannot change therefore the pumps displacement cannot change
on a fixed displacement vane pump the volume of oil will be the
sum of the capacity of the vane pockets per revolution
the capacity cannot change therefor the displacement cannot change
on a fixed displacement axial piston pump the volume of oil delivered in one revolution will be
the sum of all the pumping chambers per revolution
the volume of the chambers cannot change therefor the displacement cannot change
variable displacement pumps
are able to change the volume of the pumping chambers therefor making them variable displacement
why can gear pumps not be variable in displacement
because they are built in a housing that is unable to change its pocket size therefor making them unable to be variable displacement
how can vane pumps be variable displacement
the cam ring around the vane pockets can be moved changing the pocket size allowing for different displacement to occur
what are the three different designs of piston pumps
axial . bent axial and radial
how do piston pumps have variable displacement
by changing the stroke length of the pistons
axial piston pumps have
pistons that are parallel with the drive shaft . the pistons are in a rotating cylinder block and the other end has a shoe that slides on a swash plate
changing the swashplate angle will result in what on a piston pump
changing the length of the pistons stroke . maximum angle means maximum flow
bent axial piston pumps have
pistons that are parallel with the drive shaft and the pistons are in a rotation cylinder block the other end is held to the driveshaft in a ball and socket design
how do you change displacement on a bent axial piston pump
by moving the cylinder block in relation to the drive shaft to create different angles
how dose a reversible displacement pump change directions
they are able to reverse the path of oil flow internally by moving the swash plate
where would you most likely use a reversible displacement pump
as a hydrostatic transmission ( HST )
what could result if maximum pump input speed is exceeded
pump cavitation . because an overspeed condition dose not allow enough time for oil to completely fill the inlet of the pump
what will pump efficiency specifications tell you
how well the pump is converting mechanical energy to hydraulic energy
what are the three categories of pump efficiency
mechanical . volumetric . overall
mechanical efficiency is
an expression of the amount of power required to overcome the internal friction of the pump
volumetric efficiency is
how effectively a hydraulic pump generates flow
how do you calculate volumetric efficiency of a pump
by comparing theoretical and actual flow rate
what do all hydraulic pumps have
internal leakage
why is internal leakage important
because it is used to lubricate the internal workings of the pump
what is pump slip
when oil leaks from the outlet side of the pump to the inlet side
what two things contribute to pump slippage
increases in pressure differential between outlet and inlet side of pump and pump wear
overall efficiency is
comparing input power with the power the pump will deliver
what will cause a loss of overall efficiency at higher operating pressures
increased internal leakage and higher mechanical losses caused by internal loading
three advantages of an external gear pump
less complex . least expensive . more rugged more tolerant of contamination
two disadvantages of external gear pumps
have the lowest maximum operating pressures . variable displacement designs are not available
basic components of a external gear pump
drive gear . driven gear . housing . support bearings . o rings . internal pressure plates
why are external gear pumps considered unbalanced pumps
because the force acting on the outlet side of the pump is not counteracted by the inlet side of the pump
what is the purpose of the pressure plates in an external gear pump
to maintain good volumetric efficiency as the pressure of the pump increases
what is a unidirectional pump
operates in only one direction
what is the most identifiable feature of a bi directional pump
inlet and outlet ports are the same size . proper rotation is determined by looking and seeing what direction the gears come out of mesh
advantages of a vane pump
increased precision make them more efficient and operate at higher pressures . can be built to have variable displacement
disadvantages of a vane pump
more expensive . more susceptible to contamination damage
components of a three piece vane pump
mounting pad contains the port and is located on the front housing . center housing is machined with an elliptical opening known as a cam ring . back housing is precision machined to seal the rotor and vanes
components of a two piece vane pump
front housing supports the drive shaft and outlet ports . the rear housing contains the inlet port and houses the pumping components . pumping components are assembled as a complete unit known as a cartridge
vane pump rotor
is a cylindrical component and splined onto the drive shaft of the pump also houses the vanes
vane pump vanes
are closely fitted into slots on the rotor and when centrifugal force or high pressure oil acts on them they contact the cam ring
two common types of vane tips are
rounded and bevelled
what two forces act on the vanes of a vane pump
outlet pressure and centrifugal force
what benefits do a intra vane provide
helps reduce loading on the vane as it passes through the inlet side of the pump preventing contact without lubrication
cam ring of a vane pump provides
the surface on witch the vanes run on
elliptical cam rings are
used in balanced vanes pumps where higher pressures may be present but are a fixed displacement
circular cam rings are
used in a vane pump that has variable displacement but are also unbalanced
what is an advantage of a vane pump cartridge
can be quickly repaired by replacing the cartridge
most multiple vane pump configurations have
a common inlet port that supplies oil to each pump
a variable displacement pump that reduces its flow rate in relation to outlet oil pressure is called
pressure compensated pump
what limits maximum flow rate of a variable displacement vane pump
maximum volume stop screw
what holds the cam ring at maximum displacement on a variable displacement vane pump
compensator spring
on a intra vane design outlet pressure acts on the vane at all quadrants
true
what are three differences of a fixed vane pump vs a variable
cam ring is elliptical . there are two inlet ports opposite each other and two outlet ports opposite each other .
when changing rotation of a fixed vane pump you must
rotate the cam ring 90 degrees
how can you tell direction of rotation on a vane pump
direction of rotation is often indicated on the outside of the pump by an arrow cast into the housing
tow designs of radial piston pumps
rotating piston . rotting cam
in a radial rotating cam piston pump the pistons are
located in a fixed body and the center shaft has a cam that drives the piston out
what prevents high pressure oil from entering the pumping chamber on a radial piston pump
check valve
what makes a variable radial piston pump able to be variable
pressure builds inside acting against the spring force that normally holds it against the cam
how dose a radial piston pump balance the piston in the cylinder
by allowing high pressure oil to act on the bottom of the piston shoe equalizing pressure and hydraulically balancing the piston
