A major advantage of a positive displacement pump over a centrifugal pump is that it can

• A. Pump air, making it self-priming
• B. Deliver higher flow at the same RPM
• C. Operate with no priming
• D. Handle large solids without wear

Answer: (A)

Positive displacement pumps move a fixed amount of fluid with each cycle, so they can develop suction strong enough to draw liquid even when air is present in the system. This enables them to prime themselves and start pumping without needing an external priming step. Centrifugal pumps, by contrast, rely on continuous liquid flow and high velocity; air in the suction line breaks the flow and prevents priming, so they typically need priming to operate properly. That self-priming capability is the major advantage of a positive displacement pump. The other statements don’t capture this key trait: flow at a given RPM depends on displacement and head, not inherently higher with positive displacement pumps; “no priming” is too absolute since self-priming is possible but not guaranteed in every situation; and solids handling varies and isn’t the defining advantage over centrifugal design.