When a centrifugal pump's discharge valve is closed for a short time while running, which statement is true?

When a centrifugal pump's discharge valve is closed for a short time while running, which statement is true?

• A. The pump will stall
• B. The pump will overheat
• C. The pump will lose prime
• D. The pump is not seriously damaged

Answer: (D)

Closing the discharge valve briefly while the pump is running creates a dead-heading condition: the impeller keeps turning, but flow is blocked so the pump develops high pressure with little or no discharge. This situation doesn’t cause the rotor to seize, so it doesn’t stall. It also doesn’t cause loss of prime, since prime concerns the suction side and air or loss of suction rather than back pressure on the discharge side. For a short time, most centrifugal pumps can tolerate this backpressure without sustaining permanent damage, so not seriously damaged is the best description. The real risk would come from keeping the valve closed too long, which can lead to overheating or seal/motor stress.

Closing the discharge valve briefly while the pump is running creates a dead-heading condition: the impeller keeps turning, but flow is blocked so the pump develops high pressure with little or no discharge. This situation doesn’t cause the rotor to seize, so it doesn’t stall. It also doesn’t cause loss of prime, since prime concerns the suction side and air or loss of suction rather than back pressure on the discharge side. For a short time, most centrifugal pumps can tolerate this backpressure without sustaining permanent damage, so not seriously damaged is the best description. The real risk would come from keeping the valve closed too long, which can lead to overheating or seal/motor stress.