Water is slightly compressible.
Because of this characteristic, shock waves can occur and propagate in water piping systems.
Shock waves in pipe systems can result from sudden changes in flow such as: rapid opening of closing of control valves; starting and stopping of pumps; the recombination of water after water column separation; or the rapid exhaustion of all air from the system
When sudden changes in flow occur, the energy associated with the flowing water is suddenly transformed into pressure at that location. This excess pressure is known as surge pressure and is greater with large changes in velocity. Characteristics of the pipe such as the materials used in construction, the wall thickness, and the temperature of the pipe all affect the elastic properties of the pipe and how it will respond to surge pressures.
Avoid fast closing on-off valves
In terms of water hammer generation, manually operated valves pose few problems as long as the humans who control them are in control of their actions.
You have probably noticed that the manual closure or opening of a gate valve seldom, if ever, gives rise to water hammer. The reason is that it's almost impossible to close or open a gate valve too quickly. Quarter turn ball valves, on the other hand, seem to "want" to open and close quickly and extreme care must be used in their operation. Butterfly valves fall somewhere in between.
Automatic valves of all kinds, however, can pose a different problem. Since they are not human controlled (sometimes a good thing), they must be selected correctly.
Small, fast closing, solenoid valves will not cause water hammer 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.
It's important when selecting the actuator for an automated on-off valve, that its speed of closure be limited to a value as determined by calculation, according to the pipeline velocity and size.
If you are having water hammer issues or contemplating a new design, UVE have many years experience in helping to solve problems such as water hammer.