Why are centrifugal pumps started with their discharge valves closed?

Starting centrifugal pumps with their discharge valves closed helps avoid excessive power draw and pump damage. When a centrifugal pump is first activated, it can generate a significant amount of pressure almost immediately. If the discharge valve is open, the flow of fluid can create a situation where the pump may have to work against very little resistance, potentially leading to cavitation or overheating.

By keeping the discharge valve closed, the pump can build pressure safely. Once the pump has gained some momentum and is running efficiently, the discharge valve can be opened gradually to allow for the desired flow. This practice not only protects the pump from sudden surges in pressure but also minimizes the risk of mechanical failure and extends the life of the pump.

The other choices do not appropriately capture the rationale for this starting procedure, as the key concern is safeguarding the pump's operational integrity during startup.