Nevertheless, mainly vertical or horizontal pipelines have been analyzed, whereas in real field applications, the pipe profile is a sequence of ascending and descending pipes, with air release/vacuum valves at high points. Many authors have analyzed the problem, both from the theoretical and the experimental standpoint. Because of the difference in density between water and air, a pressure transient originates at the impact of the water column. One of the main issues arising during the rapid filling of a pipeline is the pressure transient which originates after the entrapped air has been expelled at the air release valve.
Results also showed that pressure surges decrease upon increasing the orifice diameter, except for high supply pressure and small-entrapped volume, for which an intermediate ‘critical’ orifice diameter can be identified. Water hammer only occurs because of the expulsion of air bubbles within the water column, but generally the effect on the transient is fairly negligible. In almost all the runs, the peak pressure was achieved during the mass oscillation transient. In the experiments, the orifice diameter, the supply pressure and the air volume entrapped in the descending pipe were varied.
Consequently, this paper summarizes laboratory experiments carried out on an undulating pipeline, with an orifice fitted at the high point to simulate an air release valve.
However, most studies consider horizontal or vertical pipelines, whereas the actual profile in the real field environment is a sequence of ascending and descending pipes. To analyze the transient and predict the resulting pressure surge, both theoretical and experimental studies have been developed in the literature. Severe pressure surges may arise, with detrimental effects on pipelines, valves and other devices. Transients generated by expulsion of air pockets in water pipelines represent a key issue in the management of water systems.
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