What type of pump will be damaged if started with the discharge valve closed?

• A. Positive displacement
• B. Centrifugal
• C. Axial flow
• D. Turbine

Answer: (A)

The key idea is how different pumps handle the fluid they move. A positive displacement pump moves a fixed volume of fluid with each cycle. If you start it with the discharge valve closed, that entire pumped volume has nowhere to go. The pressure in the pump and discharge line climbs rapidly until something yields—seals, gaskets, diaphragms, valves, or the housing can fail, or a relief device has to act to prevent damage. That immediate overpressure makes positive displacement pumps particularly vulnerable to starting against a closed discharge.

Other pump types don’t trap a fixed amount of fluid in the same way, so they don’t experience the same abrupt overpressure when the discharge is blocked. They may simply stall or limit flow until the discharge path is opened, but the rapid pressure rise is most characteristic and problematic for positive displacement designs.