Centrifugal pumps are classified as which type of pump?

• A. Non-positive displacement pump
• B. Positive displacement pump
• C. Rotary pump
• D. Diaphragm pump

Answer: (A)

Centrifugal pumps deliver flow by converting mechanical energy into fluid kinetic energy with an impeller. Because the flow is driven by pressure differences and varies with the system head, they don’t move a fixed amount of fluid with each cycle. In other words, the volume pumped per revolution isn’t constant and depends on pressure against the discharge side. That’s the hallmark of non-positive displacement (dynamic) pumps. In contrast, positive displacement pumps move almost a fixed volume with every cycle, delivering a nearly constant flow independent of head up to their limits. So the centrifugal type is best described as a non-positive displacement pump. The term rotary can be confusing here, since centrifugal pumps aren’t classified by a fixed displacement mechanism like other rotary positive-displacement pumps; their defining feature is continuous flow with flow rate controlled by head and speed rather than a set per-cycle volume.