Analysis of a Resonance Phenomenon in a Water Supply System

The paper deals with resonance phenomena occurred at the downstream end of a long pipe in a water supply system realized in Northern Italy. The involved pipe connects a large artificial reservoir with a group of storage tanks; it is about 30 km long and conveys water by gravity with a difference in level of 104.5 m. At the downstream end, just before the arrival in the storage tanks, the pipe is subdivided in four branches (a "comb" distribution pipe); two water hammer preventing valves and a regulating valve are installed on each branch. During the closure operation, in certain conditions, a severe pressure oscillation with high frequency and increasing amplitude was observed, suggesting the occurrence of a resonance phenomenon; it caused ground vibrations along the conduit path, also at a large distance from the valve chamber, and damages to the water hammer preventing valves.