Water hammer is caused by the compressible nature of water, resulting in shock waves in water piping systems. Shock waves in pipe systems can result from sudden changes in flow such as rapid opening and closing of control valves; starting and stopping of pumps; recombination of water after water column separation; or the rapid exhaustion of all air from the system.
Sudden changes in flow transform the energy associated with the flowing water into pressure at that location. This excess pressure is known as surge pressure and is greater with large changes in velocity. Pipe characteristics such as the materials used in construction, wall thickness, and the temperature of the pipe can affect its elastic properties and its response to surge pressures.
Manually operated valves pose few problems in terms of water hammer generation as long as the user controls the valve properly. Manual closure or opening of a gate valve rarely results in a water hammer because it is almost impossible to close or open a gate valve too quickly. Quarter turn ball valves, on the other hand, open and close quickly; therefore, extreme care must be taken in their operation. Butterfly valves fall somewhere in the middle.
Automatic valves of all kinds can pose a different problem. Since they are not human controlled, they must be selected correctly. Small, fast closing solenoid valves will not cause waterhammer because of their low flow rate. Larger ones however, can cause significant problems. Almost all valve designs can be automated and most automation systems allow selection of opening and closing times.
When selecting the actuator for an automated on-off valve, it is important to ensure that its speed of closure is limited to a value as determined by calculating the pipeline velocity and size.
Upwey Valve & Engineering can be contacted for specific solutions on water hammer issues or new valve designs.