Water hammer

Water hammer is the consequence of a hydraulic transient. The transient that is the most extreme, and is therefore most easily understood, is "pressure rise" associated with sudden valve closure on flow reversal, say, when a pump stops due to power failure.

However, in the real world, there is no such thing as sudden valve closure, and transients happen all the time, when pumps start, stop, valves open and close, flow reversal occurs due to changes in demand, etc.

Protection against damage caused by transients that result in conditions not planned (i.e. designed) for require careful and specific analysis.

Regarding pressure relief (do nothing to relieve transient conditions), air and vacuum valve (allow air to enter pipeline on column separation and can be effective) surge tanks (must be sized to catch the "wave"), VFDs (effective at reducing transients with slow start and stop, provided there is power), timed valves (timing is critical, and may be long 45-60 seconds, or very short).

All of the above may play roles in controlling transients so that the pressure rating of the piping system is not exceeded. Before implementing any of them, a high degree of understanding of the conditions leading to transients, the high pressure associated with transients and their location must be known.

There is no product solution to this problem, nor is there a blanket recommendation that should be employed. Transient analysis is a specialized field of hydraulics, and although there are many tools (analytical models) available, experience and knowledge are required to effectively use these tools and solve the problems.