If a centrifugal pump has a discharge head that is too high, what is the effect on the discharge rate?

If a centrifugal pump has a discharge head that is too high, what is the effect on the discharge rate?

• A. No change
• B. Decreases discharge rate
• C. Increases discharge rate
• D. Causes backflow

Answer: (B)

The main idea is how system head and pump capacity interact on a centrifugal pump’s performance curve. A centrifugal pump moves water by overcoming the head the system requires. The operating point—the actual discharge rate—occurs where the pump’s head vs. flow curve intersects the system’s head curve. If the discharge head required by the piping is too high, the pump cannot push as much water at that higher resistance. The operating point shifts to a lower flow on the pump curve, so the discharge rate decreases. If the head demand becomes very large, the flow could approach zero, but the typical result is reduced discharge rather than no flow or reversed flow.

The main idea is how system head and pump capacity interact on a centrifugal pump’s performance curve. A centrifugal pump moves water by overcoming the head the system requires. The operating point—the actual discharge rate—occurs where the pump’s head vs. flow curve intersects the system’s head curve.

If the discharge head required by the piping is too high, the pump cannot push as much water at that higher resistance. The operating point shifts to a lower flow on the pump curve, so the discharge rate decreases. If the head demand becomes very large, the flow could approach zero, but the typical result is reduced discharge rather than no flow or reversed flow.