D-5. Alternatively, surge pressures may be reduced by provision of a pressure relief valve at the pumping
station as illustrated in figure D-3. The initial effects of pump shutdown are unaltered but the relief valve
opens as flow reverses towards the station. Flow impact on the closed check valves is therefore avoided and
surge pressures are reduced to 637 feet (276 PSIG).
D-6. This case study illustrates the fact that an uncontrolled surge due to pump shutdown, in combination
with an arbitrary factor of safety for the pipeline and check valve pressure ratings could cause system failure.