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.
Mixed Flow Impellers:
This design develops pressure/head through centrifugal and axial forces. It is generally used where a High Flow – High Head installation is required. The angle at which the fluid is discharged at an angle less than 90° from the eye of the impeller. Nominal rates are generally in the range of from 1200 bpd to 70,000 bpd, but with pump efficiencies greater than 60%. This is the more popular of the two designs, because they handle gas and solids more efficiently.
Radial flow impellers:
This design develops pressure/head through centrifugal forces. It is generally used where a low flow, high head installation is required. This design is accomplished by allowing the fluid to be discharged at a 90° angle from the eye of the impeller. Nominal rates are in the range of from 100 bpd to 1200 bpd with pump efficiencies in the order of 60%. The radial stage is a flat stage and is the most efficient design for these lower flow rates.