There are mainly two designs of electrical submersible pump stages widely used by ESP’s service companies:
Fixed impeller or compression pump design: every impeller is fixed to the shaft and is not free to move up and down. Hence, it cannot move without the shaft moving. All the impellers are “compressed” together to make one rigid body.
Floating stage design: each impeller in a floater pump is free to move up and down on the shaft within the confines of the diffuser as depicted in the following Figure. The thrust washers on the impeller support the stage thrust. The amount of thrust varies with liquid rate (the amount of fluid being pumped).
A “ Pump Stage ” consists of an impeller, diffuser and thrust washers.As shown by the following figure, the impellers rotate with the shaft and spin at the RPM of the motor. The stationary diffusers turn the fluid into the next impeller and do not rotate. Pumps are assembled by stacking stages on a shaft and compressing the stack in a housing. A stage will produce a given amount of flow and lift (head) at the motor RPM.
The pump stages are of a fully enclosed curved vane design, whose maximum efficiency is a function of impeller types and designs. There are two basic types of stages used in oil well submersible pumps: stages with Mixed flow impeller and stages with Radial flow impeller.
The difference between these two types of designs is described by the pump impeller vane angles and the size and shape of the internal flow passages, as depicted in the graphs below.