Closing the discharge valve on a centrifugal pump will:

• 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)

Shutting the discharge valve on a running centrifugal pump forces the flow to zero, so the pump operates at zero flow on its performance curve. At that point the head it can develop is its shut-off head—the maximum head the pump is capable of delivering. The static head, set by the system’s elevations, doesn’t change with the valve closure, so closing the discharge valve doesn’t increase the system’s static head. In practice, this test reveals the pump’s maximum capability, though abrupt closures can cause pressure transients in some systems.