Transient Effects of Surge Vessel Sizes and Locations in a Water Transmission Line

Water transmission main is subjected to hydraulic transients due to sudden pipe failure, valve closure or any other transient phenomenon. These hydraulic transients might cause adverse effect within the pumps, bursting of the transmission main and detachment of the pipe from the joint locations such as air valve or control valve. The negative transient pressures can cause water quality issues especially from intrusion of contaminants from at the air valves and loose joints. In order to avoid both unacceptable minimum and maximum transient pressures, surge protection is imperative for a water transmission main. It is a common practice to locate the surge vessel near the pumps in order to dampen the generated surge due to sudden pump failure. In this study, surge analysis results considering two different topology configurations (Option 1 & 2) with respect to different surge vessel locations are compared for a water transmission main connected to two pumps (each having a capacity of 14.5 l/s @ 110 m head ) in parallel. The transmission main is serving residential consumers which are located on 50 m higher elevation from the pump station at a distance of about 12.5 KM. For Option 1, it is considered that two surge vessels are placed on a 150 mm DI line, 2.5 m far at the downstream side of each pump. For Option 2, only one surge vessel is placed on a 300 mm transmission main originating just after the parallel connection of the 150 mm DI lines at the downstream of the two pumps. Transient analysis is undertaken for different vessel sizes of two configurations. The results obtained are compared for the Minimum Transient Pressures in the modelled pipeline. Although, comparative difference between the two configurations is not much but gives a clear indication that surge vessel location and sizes could play a vital role in controlling the transient pressures. It is also observed that the pre-charge pressure in the surge vessel is also very important for controlling the transient pressures and must be precisely determined with respect to the mechanism of the working of the selected surge vessel.