Jim Gugich, Director A water supply system is subjected to water hammer whenever there is a change in steady state condition such as pump stoppage, pump startup or valve closure. As a system changes from one steady state condition to another there is a transient change in flow and pressures as the system settles to the final steady state condition. The magnitude of transient pressures (or water hammer) and the time duration of the transient condition depends on the flowrate velocity, pipeline material and the system boundary conditions such as tanks, pumps, air valves, control valves and changes in pipeline diameter. The phenomenon of water hammer is generally poorly understood in the water industry. This is due to the difficulty in carrying out a comprehensive analysis, which considers all the system components and their interaction. It is not uncommon for designers to simply add a nominal pressure increase to allow for water hammer. This approach can be too conservative and unnecessarily costly and in some cases there have been system failures due to inadequate water hammer protection being provided. The undertaking of a water hammer analysis, and selection of protection measures, should be an integral part during the design phase. There are now propriety water hammer programs available, which can assist designers in identifying potential water hammer problems and help in the selection protection measures. The use of these programs should be limited to experienced designers with intimate knowledge of water distribution systems. Download the complete story as a Word Document BACK TO