A centrifugal pump can be started or stopped against what condition?

• A. High head
• B. Low suction
• C. Open discharge valve
• D. Closed discharge valve

Answer: (D)

Starting or stopping a centrifugal pump against a closed discharge valve is advised because it limits the hydraulic load during acceleration or deceleration. With the discharge valve shut, there is essentially no flow in the discharge line, so the pump develops its maximum head (near shut-off) but moves little water. This prevents a sudden surge of flow and pressure in the piping, reducing the risk of water hammer and mechanical stress on the pump, piping, and valves. Once the pump has reached speed, the valve can be opened gradually to bring the system online in a controlled way. Similarly, closing the valve during shutdown helps avoid abrupt pressure changes in the system.