Centrifugal pumps are classified as which type of pump?

• A. Non-positive displacement
• B. Positive displacement
• C. Rotary
• D. Diaphragm

Answer: (A)

Centrifugal pumps are dynamic, non-positive displacement machines. They achieve flow by spinning an impeller to impart velocity to the fluid and then converting that velocity into pressure in the casing. Because no fixed volume is trapped per rotation, the flow is continuous and its rate varies with the system head and speed rather than being a fixed amount per cycle. At a given speed, increasing head reduces flow, and increasing speed increases flow, but there isn’t a guaranteed volume per revolution. In contrast, positive displacement pumps trap a specific amount of fluid with each cycle, delivering a nearly constant flow at a given speed, which is why choices like diaphragms or other positive-displacement types don’t describe centrifugal pumps.