Which type of pump should not be started with the discharge valve closed?

• A. Centrifugal pump
• B. Gear pump
• C. Piston pump
• D. Diaphragm pump

Answer: (C)

When a pump is started with the discharge valve closed, you create a deadhead condition—no fluid can leave the pump. The way the pump handles that depends on the type.

Piston pumps are positive-displacement machines that push a fixed amount of fluid with each stroke. If the outlet is blocked, that whole volume has nowhere to go, so the pressure in the discharge line shoots up very rapidly. This sudden pressure spike puts extreme stress on seals, valves, and the piston rod, and can damage the pump or cause a failure if there’s no relief path. That’s why this type should not be started with the discharge valve closed; it’s the most sensitive to deadheading.

The other pump types are less prone to immediate, severe damage from starting with the discharge closed, though it’s still not good practice to deadhead them. The piston pump’s fixed-volume, reciprocating action makes it especially dangerous under that condition, which is why it’s singled out as the one not to start with the discharge valve closed.