Which statement best describes a key capability of positive displacement pumps compared to centrifugal pumps?

Which statement best describes a key capability of positive displacement pumps compared to centrifugal pumps?

• A. It can pump air, making it self-priming
• B. Delivers higher throughput at the same RPM
• C. Requires no priming at startup
• D. It is less affected by viscosity

Answer: (A)

Self-priming is the defining capability here. Positive displacement pumps move a fixed volume with each cycle, and their sealed chambers can create suction even when air is present in the suction line. As the chamber expands on the intake stroke, it pulls in liquid and can draw air through the line until the pump and line fill with liquid. Once primed, the pump continues to discharge fluid with each stroke. Centrifugal pumps, on the other hand, rely on a continuous column of liquid and lose prime if air breaks that column, so they generally can’t start pumping without manual priming. That ability to remove air and start pumping without external priming makes positive displacement pumps self-priming.

Self-priming is the defining capability here. Positive displacement pumps move a fixed volume with each cycle, and their sealed chambers can create suction even when air is present in the suction line. As the chamber expands on the intake stroke, it pulls in liquid and can draw air through the line until the pump and line fill with liquid. Once primed, the pump continues to discharge fluid with each stroke. Centrifugal pumps, on the other hand, rely on a continuous column of liquid and lose prime if air breaks that column, so they generally can’t start pumping without manual priming. That ability to remove air and start pumping without external priming makes positive displacement pumps self-priming.