Never start a ____ pump against a closed discharge.

• A. positive displacement
• B. centrifugal
• C. axial flow
• D. reciprocating

Answer: (A)

Starting a pump when the discharge is closed creates a deadhead condition. The key point with positive displacement pumps is that they move a fixed volume of fluid with each cycle or rotation, regardless of the discharge pressure. If the discharge path is blocked, that trapped fluid has nowhere to go, so the pressure in the discharge line rises rapidly. This can push past the pump’s design limits, overloading the drive, and damaging seals, fittings, and piping.

Because of this fixed-volume behavior, positive displacement pumps are particularly dangerous to start against a closed discharge. Centrifugal and axial-flow pumps rely on dynamic head and will typically stall or reach a relief condition rather than continue moving a fixed volume against a closed valve, making the risk profile different. Reciprocating pumps are a type of positive displacement pump, so they share the same hazard.

Always ensure the discharge is open (or a proper bypass/relief is in place) before starting any pump, especially positive displacement types.