Pressure surges during filling of partially empty undulating pipelines

Transients generated by expulsion of air pockets in water pipelines represent a key issue in the management of water systems. Severe pressure surges may arise, with detrimental effects on pipelines, valves and other devices. To analyze the transient and predict the resulting pressure surge, both theoretical and experimental studies have been developed in the literature. 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. 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. In the experiments, the orifice diameter, the supply pressure and the air volume entrapped in the descending pipe were varied. In almost all the runs, the peak pressure was achieved during the mass oscillation transient. 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. 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.