A ___ pump running in the wrong direction will deliver some liquid but not as much as the normal pumping rate.

• A. Positive displacement
• B. Centrifugal
• C. Diaphragm
• D. Gear

Answer: (B)

In a centrifugal pump the liquid is moved by throwing it outward with the rotating impeller, then collecting it in the casing and sending it to the discharge. The impeller and casing are designed to direct flow efficiently in one direction, so when the pump runs backward the energy transfer to the fluid is no longer optimized and the pump cannot reach its normal discharge rate. You can still see some liquid because fluid can leak around seals and through clearances and the impeller still pushes a bit of liquid in the reverse direction, but the overall flow is much lower.

Positive-displacement pumps (like gear or diaphragm types) rely on fixed-volume transfer and check valves to control flow. When run in the wrong direction, these valves and the mechanism prevent normal forward flow, so they deliver little to no liquid.