What type of pump is a diaphragm pump?

• A. Centrifugal
• B. Axial-flow
• C. Negative displacement
• D. Positive displacement

Answer: (D)

A diaphragm pump works by changing the volume of a sealed chamber with a flexible diaphragm. As the diaphragm moves, the chamber volume increases to draw fluid in, and then decreases to push fluid out. Each complete stroke displaces a fixed amount of liquid, which is the hallmark of a positive displacement pump. That fixed-volume operation is what sets it apart from centrifugal or axial-flow pumps, which move fluid mainly by imparting velocity with impellers and rely on dynamic pressure rather than fixed-volume displacement. Negative displacement isn’t a standard classification for pumps, so it isn’t applicable here.