Which valve should be throttled to start a centrifugal pump?

To properly start a centrifugal pump, the discharge valve should be throttled. This is because a centrifugal pump requires a certain amount of back pressure to operate efficiently. When the discharge valve is partially closed, it creates a controlled pressure in the system, allowing the pump to build up the necessary head and flow rate gradually.

This throttling action helps prevent potential damage to the pump from excessive flow or cavitation, which can occur if the pump is started against a fully open discharge line. By controlling the flow with the discharge valve, operators can ensure that the pump starts smoothly and reaches its operational parameters safely.

In contrast, the inlet valve, bypass valve, and drain valve each have different roles within the system. The inlet valve controls the flow of fluid into the pump, which is crucial but not the valve that needs to be throttled at startup. The bypass valve helps redirect flow when needed, while the drain valve is used to remove fluid from the system, neither of which is appropriate for starting the pump. Thus, throttling the discharge valve is the correct practice for initiating the operation of a centrifugal pump.