Reciprocating positive-displacement pumps are also known as which type?

• A. Air-lift pumps
• B. Centrifugal pumps
• C. Piston pumps
• D. Pneumatic ejector

Answer: (C)

Reciprocating positive-displacement pumps move a fixed amount of fluid with each back-and-forth stroke of a piston inside a cylinder. That back-and-forth motion, delivering a specific volume per cycle, defines them as piston pumps. The other options don’t share this mechanism: air-lift pumps use compressed air to lift water without a fixed-volume displacement per stroke; centrifugal pumps rely on a rotating impeller to impart energy and move fluid, not by a per-stroke displacement; pneumatic ejectors use an air jet to create suction or move fluid rather than a reciprocal piston action.