In a centrifugal pump, how does flow relate to head along the pump curve?

• A. Flow increases with head along the pump curve.
• B. Flow is independent of head.
• C. Higher head yields higher flow; the pump curve shows that relationship.
• D. On the pump curve, higher head corresponds to lower flow.

Answer: (D)

The main idea is that a centrifugal pump curve shows an inverse relationship between head (pressure rise) and flow for a given speed. For a fixed speed, the head the pump can develop is highest at zero flow (shut-off head) and decreases as flow increases. This happens because as you try to push more water, the velocity-energy added by the impeller is spread over more flow, and energy losses grow, so the attainable head drops. The operating point is where the system head equals the pump head, so when system head is high, the flow is low, and when system head is low, the flow is high. That’s why higher head corresponds to lower flow along the pump curve.