Which describes a rotary pump's method of displacing fluid?

• A. Uses vibrating diaphragms
• B. Uses rotating screws, lobes, gears, or vanes
• C. Uses centrifugal force
• D. Uses magnetic fields

Answer: (B)

Rotary pumps displace fluid by trapping a fixed volume in cavities formed by rotating elements (such as gears, screws, lobes, or vanes) and moving that fluid from the suction side to the discharge side as the parts turn. Each rotation carries a precise amount of fluid, making the flow steady and well-suited for viscous liquids. This positive-displacement action is the hallmark of rotary pumps.

Vibrating diaphragms use a flexible membrane that expands and contracts to draw in and push out fluid, which is not a rotating displacement mechanism. Centrifugal pumps rely on an impeller to accelerate fluid and convert velocity into flow, not on fixed-volume cavities, so they don’t displace fluid in the rotary positive-displacement sense. Magnetic-field-driven pumps can drive motion, but the fundamental displacement method here is defined by rotating cavities, not magnetic actuation.