fixed-displacement unbalanced vane pump

FIXED-DISPLACEMENT UNBALANCED VANE PUMP

1. Construction and Operation

Fig.4.11 illustrates a typical unbalanced sliding-vane pump with fixed delivery.

In this pump, the rotor is mounted off-center. At regular intervals around the curved surface of the rotor are rectangular vanes that are free to move in a radial slot. As the rotor revolves, the vanes are thrown outwards by centrifugal force to form a seal against the fixed casing. The eccentricity of the revolving rotor produces a partial vacuum at the suction side of the pump, causing an inflow of liquid. This is carried to other side of the pump in the space between the rotor and the fixed casing.

Generally, pumping rates of these rotary pumps are varied by changing the speed of the rotor. However in unbalanced vane pumps, th pumping rate can also be varied by changing the degree of eccentricity of the rotor, since this determines the amount of liquid carried through per cycle.

In the fixed displacement pump, the rotor-housing eccentricity is constant. Hence the displacement volume is fixed. A constant volume of fluid is discharged during each revolution of the rotor.

Note

1. This pump is referred as unbalanced pump because all of the pumping action takes place on one side of the rotor. This causes a side load to the rotor, as shown in Fig.4 1.

2. In addition to sliding vanes, rolling vanes and swinging va are also available in unbalanced vane pumps. Each of these variations is hydrostatically unbalanced. This unbalance causes high bearing loads and generally limits the application of unbalanced vane pumps to operating pressures less than about 100 bar.