Hydraulic shock (or more commonly Water Hammer) is a pressure surge caused when a fluid in a high pressure system is forced to stop or change direction suddenly. It is commonly caused when a fluid's flow is interrupted suddenly in a pipe system causing the propagation of shockwaves.
On the other hand, in situations where an upstream valve has been shut, the flowing fluid can create a vacuum behind it, which can result in damage to the pipe and in extreme cases, the pipe collapsing.
Hydraulic shock is present in metal and plastic systems, and will strain tube and fittings alike, but is more visible in metal systems due to their ability to transmit sound. It can cause major problems, from noise and vibration to pipe rupture and needs consideration during system design especially when pipes are transporting hazardous liquids and gases.
When a flow in a system is interrupted suddenly, the fluid before the breakpoint is still flowing causing a build up of pressure and a resulting shock wave. The greater the flow of water, the greater the resulting shock wave will be.
In a domestic system this is typically caused by taps, valves or appliances such as dishwashers, washing machines and toilets.
Mitigating the effects of Hydraulic Shock
To prevent the damage of water hammer, you need to eliminate the shock waves. In this way the shockwaves can be reduced or even eliminated through the use of valves that close slowly rather than suddenly.
In the case that fast-action valves are required, measures can be taken to reduce the size of the shockwaves by reducing the flow of the water. Other actions may include: