TM 5-813-9
D-3. The magnitude of the initial pressure drop and subsequent surge pressure is influenced by the initial
pipeline velocity, the static head, the pipeline length, pressure pulse wavespeed, and friction. The system
illustrated has over 550 feet (238 PSIG) static lift which produces the reverse accelerating head to cause a
peak pressure of 1085 feet (470 PSIG). The peak pressure is attenuated to some degree by the action of air
valves on the pipeline which opened when the initial pressure drop or downsurge traversed the system. This,
together with the interaction of velocity changes in the pipeline, causes the inflections in the pressure history
shown in the plot.
D-4. Figure D-2 illustrates the effectiveness of an air vessel or accumulator on the same system. Rapid
velocity changes are prevented following pump shut down; instead water flows from the air vessel and the
pipeline flowrate drops steadily. In turn, the pressure falls slowly and mass oscillation develops between the
air vessel and the pipeline terminus.
D-2
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