HYDRAULICS VANE PUMP

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.