CASE STUDY FOR HYDRAULIC TRANSIENTS
D-1. In a typical water pump station operating on suction level control, pump stop and restart occurs
several times each day. Pump shutdown is the most common cause of hydraulic surge pressures or hydraulic
transients in this type of system. Valve closure surges may be less frequent.
D-2. Figure D-1 illustrates a typical pressure/time history obtained at the pump discharge manifold of a
pumping station following pump shutdown. As the pumps stop, flow into the pipeline drops rapidly; but the
column of liquid in the line continues under its own momentum leaving behind a low pressure region.
Eventually the momentum is overcome by the opposing force of static head which in turn accelerates the
liquid column back towards the pumping station. The pump discharge check valves close in this interim
period and a rapid pressure rise occurs when reverse flow impacts on the closed check valves approximately
6 seconds after pump shutdown.