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.