You find that the check valve on a centrifugal pump is leaking. When would the most damage be caused to the pump?

• A. During shutdown
• B. On startup of the pump
• C. During steady operation
• D. At random times

Answer: (B)

The most damage happens during startup because that is when the pump is rapidly ramping up flow and head. If the check valve leaks, some of the discharge can flow back into the suction side as the pump accelerates, creating a reverse or recirculating flow through the impeller. This introduces large transient forces and pressure spikes (a water-hammer-like effect) in the pump and piping just as seals, bearings, and the impeller are beginning to work and warm up. Those sudden surges and reverse flows put the highest stress on rotating components and seal faces. In steady operation the flow is balanced and backflow is limited, so damage risk is much lower. During shutdown the energy in the fluid is winding down, so while transients can occur, they’re typically less severe than the startup surge.