Why large centrifugal pumps are started with discharge valve closed?

It is common practice to start large capacity centrifugal pumps (such as saltwater circulating pump and freshwater circulating pumps) with the discharge wall closed.

If the characteristics curves for a centrifugal pump are examined, it will be seen that when the quantity of water discharged is zero, the power required by the pump is zero or a very small amount.

By starting the pump with the discharge valve closed the power demand made by the pump on the pump motor is kept to a very minimum.

After the pump has started and the momentary high motor current demand has stabilized, the discharge valve is opened.