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Title: REDUCTION OF WATER LOSSES CAUSED BY PRESSURE TRANSIENTS USING AIR VALVES

Author: S. Yaniv and N. Zloczower

Year: 2009

Publisher: European Water Resources Association (EWRA)

Description:

The demand for water is increasing due to population growth and technology development whereas water is becoming a scarce resource. The concern for water losses has grown to a global concern and there is an urgent need to find innovative solutions for water loss in water supply systems. Many water utilities ascribe their high seasonal burst frequencies to pressure transients. Pressure transients cause cracks and unseen small breaks in buried pipelines, pipe fittings and accessories and also can cause severe pipe ruptures and pipe bursts. These
damages result in leakage and can bring to financial losses and to water shortage at times of scarcity. Control of pressure transients can greatly reduce the formation of these damages and consequent leakage. Recent studies have shown that presence of air pockets of certain sizes can intensify the strength of upsurges and produce a burst in the pipe. Entrapped air appears not only during the filling or draining of the pipes but also during the normal operation of the system. Entrapped air reduces the transportation capacity of the pipe producing additional head losses and thus energy losses. Absence of air can cause collapse of the pipe due to sub-atmospheric (negative) pressures. In some cases, the absence of an air cushion can increase the damages of pressure transients. Air valves are the most cost effective tools for the control of minor transients and in many cases for the control of major transients. They are used to ensure the release of the entrapped air accumulated during the normal operation of the system and the filling of pipes. They are also installed to suppress  sub-atmospheric pressures by admitting air rapidly to avoid cavitation and subsequent column separation during
drainage and system shutdown. By reducing negative pressure transients, air valves reduce positive pressure transients. Furthermore, well sized, quality combination air valves prevent the formation of vapor cavities and, thus, prevent extreme upsurges. Case studies conducted in Russia showed that air valves were found very effective in reducing water losses (pipe burst and leakage) by 15% and increasing the energy saving by more than 20%.