VANE PUMP
A rotor
is mounted in a elliptical casing between closely fitted end plates. The slots,
which are made radially in the rotor carries the vanes in it. The rotor shaft
is located in escentrically in relation to the housing when rotor rotates the
vane proceed from the point of shortest distance between rotor and housing
increased space will be created between rotor and housing. This space fills
with oil supplied through a peripheral value slot from the suction port. After the maximum distance between rotor and housing
has been passed. The space between rotor and housing decreases and oil is
discharged through the opposite value port. The vanes are sliding out up to the
outer track by means of centrifugal force. As the centrifugal force is
insufficient to hold the vane against the track during high pressure, the
pressure of oil is applied to the bottom of vanes through drilled holes and semi-circular
groove made on the end plates. In this design the rotor is subjected to a
heavy, unbalanced load the hydraulic pressure in the discharge area acts
against the rotor resulting in heavy loading of the rotor bearings. This
difficulty has been avoided by providing two intake and two discharge
.diametrically opposite each other and thus the hydraulic loads on the rotor
balance each other.in this design the vane track is made elliptoid instead of
circular, having two minimum and two maximum centre distance
Vane
pumps are being made in both constant and variable discharge design the
volumetric efficiency of vane pump is 90% and over. The direction of flow can
be reversed by reversing the rotation of the pump
vane
pump requires great accuracy and close tolerance .commercial vane pumps are
provided separate valve plates (port slot plate).the space in between suction
and discharge ports called lap space is equal to the pitch distance of the
vanes .in addition to the single pump a great number of combination of pumps
are available these combination consists of two or more pumping units mounted
in one casting
CONSTRUCTION MATERIALS
Externals
(head, casing) - Cast iron, ductile iron, steel, and stainless steel.
Vane, -
Carbon graphite,
End Plates -
Carbon graphite
ADVANTAGES
OF VANE PUMP
Vane pumps are robust,
self-priming.
Vane pump provides uniform
discharge with negligible pulsations.
Vane pump vanes are
self-compensating for wear.
The vanes can be easily
replaced.
These pumps don't require check
valves.
They have relatively high
efficiency.
DISADVANTAGES
OF VANE PUMP
Vane pumps cannot handle abrasive liquids.
Complex housing and many parts
Not suitable for high viscosity
Not suitable for high
pressures , the pressure within the pump chamber increases, the vanes
begin to lose the ability to maintain contact with the walls of the pump
chamber.
TYPES OF VANE PUMP
There are two important types of vane pumps that are used in day today
life:
1. Unbalanced vane pumps
a) Fixed displacement unbalanced pump
b) Variable displacement unbalanced pump
2. Balanced vane pump
1.UNBALANCED VANE PUMP
In the unbalanced vane pump,
the rotor is mounted elliptical casing as off center. The rectangular vanes
fitted radially on rotor slots regular intervals, these rectangular vanes are
free to move in the radial slot. The vanes are thrown outwards due to the
centrifugal force to form a seal against the fixed casing as the rotor starts
to rotate. The eccentricity of the revolving rotor produces a partial vaccum at
the suction side of the pump which causes the inflow of the liquid. This is
carried to other side of the pump in the space between the rotor and the fixed
casing. the pumping action occurs in the chambers on one side of the
rotor and shaft. This design imposes a side load on the rotor and drive shaft. The pumping
rates of these rotary pumps are varied by changing the speed of the rotor. But
in unbalanced vane pump, the pumping rate can also be varied by varying the
degree of eccentricity of the rotor, since this determines the amount of liquid
carried through per cycle.
(a) Fixed displacement unbalanced vane pumps
In the fixed displacement unbalanced vane pump, a constant volume of
fluid is discharged during each revolution of the rotor that is provided. This
achieved by keeping the rotor housing eccentricity as constant and therefore
the displacement volume is fixed.
(b)Variable displacement unbalanced vane pump
In the variable displacement unbalanced vane pump the housing can be moved with
respect to the rotor. This movement changes the eccentricity and the
displacement can also be varied. A hand wheel or pressure compensator can be
used to move the can ring and thus to change the eccentricity.
2.BALANCED VANE PUMP
In the balanced vane pump, it consists of two intake ports and two
outlet ports and they are diametrically opposite to each other. And also in the
balanced vane pump an elliptical housing is used in balanced vane pump rather
than cam ring that is used in unbalanced vane pump. This configuration creates
two diametrically opposed volumes. The two high pressure zones balance the
forces on the rotor shaft and hence complete hydraulic balance is achieved.
These descriptions are the only difference from unbalanced vane pump other than
this construction and working principle is as same as the unbalanced vane pump.
