What type of pump consists of an impeller fixed on a rotating shaft enclosed in a casing with an inlet and discharge, and can be opened against a head?

• A. Submersible Pumps
• B. Positive Displacement Pumps
• C. Centrifugal Pumps
• D. Axial Flow Pumps

Answer: (C)

This question is testing your ability to recognize a centrifugal pump by its basic construction and how it develops pressure. A centrifugal pump has an impeller fastened to a rotating shaft inside a casing with an inlet (eye) and a discharge. As the impeller spins, fluid is drawn in through the inlet and flung outward by centrifugal force, moving into the casing and out the discharge. This action builds pressure, or head, so the pump can push fluid against system resistance. Being able to be “opened against a head” means the pump can deliver flow even when the discharge side is under pressure, within its performance curve set by speed and impeller size.

Submersible pumps are defined more by being sealed and operated underwater, not by this impeller-and-casing arrangement. Positive displacement pumps deliver a set volume per rotation and don’t rely on centrifugal forces to generate head. Axial flow pumps push fluid mainly along the axis of the impeller, with a different flow pattern from centrifugal action. Therefore, the described configuration corresponds to a centrifugal pump.