Which valve condition can cause backflow through a pump, potentially reversing the shaft?

• A. Open discharge valve
• B. Faulty check valve
• C. Bypass valve
• D. Loose valve stem

Answer: (B)

A valve that stops backflow is a check valve, placed on the discharge side to prevent fluid from flowing backward through the pump. If that check valve is faulty, it may not seal properly and backflow can occur through the pump. When liquid starts moving backward through the impeller, it can impart reverse torque on the shaft, potentially turning the shaft in the opposite direction or placing abnormal stress on bearings and seals. That’s why a faulty check valve is the condition most capable of causing backflow through a pump and possibly reversing the shaft.

The other valve conditions don’t create this reverse-through-the-pump risk in the same direct way. An open discharge valve affects downstream flow but doesn’t guarantee backflow into the pump. A bypass valve can divert flow around the pump rather than back through it. A loose valve stem may cause leaks or control issues, but it doesn’t specifically enable reverse flow through the pump.