Why is surge pressure a critical concern in positive displacement pumps?

Surge pressure is a critical concern in positive displacement pumps because these pumps deliver a fixed volume of fluid with each stroke or revolution, and any sudden blockage or rapid valve closure downstream can cause a rapid and substantial increase in pressure, potentially leading to equipment damage or failure. Positive displacement pumps, such as reciprocating pumps (piston, plunger, diaphragm) and rotary pumps (gear, screw, vane), operate by trapping a fixed volume of fluid and forcing it through the discharge line. Unlike centrifugal pumps, they do not rely on imparting kinetic energy to the fluid; instead, they provide a constant flow rate regardless of the discharge pressure. When a valve downstream of a positive displacement pump is suddenly closed, or if there is a blockage in the line, the fluid being pumped has nowhere to go, causing a pressure wave to propagate back through the system. This pressure wave, known as surge pressure or water hammer, can be several times higher than the normal operating pressure of the pump and piping. The high pressure can cause pipes to rupture, fittings to leak, and pump components to fail. For instance, if a positive displacement pump is used to inject chemicals into a pipeline, and a check valve downstream suddenly closes, the resulting surge pressure could damage the pump or the injection point. Therefore, pressure relief valves or surge dampeners are often installed in positive displacement pump systems to protect against surge pressure.