Which pump type is not a positive displacement pump?

Which pump type is not a positive displacement pump?

• A. Centrifugal pump
• B. Reciprocating pump
• C. Rotary pump
• D. Diaphragm pump

Answer: (A)

This question tests the difference between positive displacement pumps and dynamic (non‑positive‑displacement) pumps. A positive displacement pump moves a fixed volume of fluid with each cycle, so the flow rate is essentially tied to the pump speed and displacement, and it can develop high pressure even at low flow. Reciprocating, rotary, and diaphragm pumps all fit this category because they deliver a specific amount of fluid per cycle regardless of the system pressure (within operating limits). A centrifugal pump is not a positive displacement pump. It’s a dynamic pump that uses an impeller to add velocity to the fluid and then converts that velocity into pressure. The amount of fluid it moves per revolution isn’t fixed; the actual flow depends on the system head and speed. As head increases, flow tends to drop, and at zero discharge there isn’t a defined fixed volume being pumped. This characteristic sets centrifugal pumps apart from the others listed, which produce a nearly fixed volume per cycle.

This question tests the difference between positive displacement pumps and dynamic (non‑positive‑displacement) pumps. A positive displacement pump moves a fixed volume of fluid with each cycle, so the flow rate is essentially tied to the pump speed and displacement, and it can develop high pressure even at low flow. Reciprocating, rotary, and diaphragm pumps all fit this category because they deliver a specific amount of fluid per cycle regardless of the system pressure (within operating limits).

A centrifugal pump is not a positive displacement pump. It’s a dynamic pump that uses an impeller to add velocity to the fluid and then converts that velocity into pressure. The amount of fluid it moves per revolution isn’t fixed; the actual flow depends on the system head and speed. As head increases, flow tends to drop, and at zero discharge there isn’t a defined fixed volume being pumped. This characteristic sets centrifugal pumps apart from the others listed, which produce a nearly fixed volume per cycle.