The seal is sometimes referred to as a protector and has 5 main functions:

-          Equalize the pressure in the motor with that of the wellbore

-          Prevent well fluid from getting into the motor

-          Provide a reservoir for the motor oil to expand and contract

-          Provide a thrust bearing for down thrust loading

-          Transmit the torque from the motor to the pump

When designing the seal the size of the pump, type of well fluid, size of motor and deviation of the well need to be taken into account. These will not only determine metallurgy, shaft size and thrust bearing size, but determine the type of the protector, which could be:

-          Labyrinth Style

-          Positive Seal (Bag) Type

-          Metal Bellows Type

With the above designs there are elastomer considerations that will determine the type of well bore fluids and temperatures each of these can handle.