What happens when closing the discharge valve on a centrifugal pump?

• A. Over-pressurize discharge piping, causing damage
• B. Identify the maximum head the pump can develop
• C. Increase the total static head
• D. Create water hammer and damage the valve

Answer: (B)

Closing the discharge valve causes flow to drop to zero, and the pump then develops its maximum pressure—the shut-off head. This is the highest head the pump can produce when there’s no flow, so closing the valve tests the pump’s maximum capability to build pressure. The static head, determined by elevations and fixed in the system, doesn’t change with the valve position. If the valve is closed very quickly, a transient surge (water hammer) can occur in the piping, but the fundamental outcome is the pump reaching its shut-off head.