Shut a tap quickly and listen: a dull bang, sometimes a shudder through the wall. That is water hammer, and it is the single most underrated cause of leaks in domestic systems.
What is actually happening
Water is heavy and does not like stopping. When a valve closes fast, the moving column of water has nowhere to go and converts its momentum into a pressure spike, easily several times normal working pressure. The spike bounces back and forth through the pipework until friction eats it. The bang you hear is pipes taking the hit.
Why you should care
One spike does nothing. Ten thousand spikes over years fatigue joints, weep seals and split weak fittings, usually at the worst joint in the system. Pumps with hard on-off switching produce hammer every cycle. So do solenoid valves on irrigation manifolds, slamming shut dozens of times a day.
The fixes
- Slow the valve. Quarter-turn taps and fast solenoids are the worst offenders. Slow-closing valves remove most of the spike.
- Give the pressure somewhere to go. A small air chamber or expansion vessel near the fast valve absorbs the surge.
- Soften the pump. Variable-speed or soft-start control eliminates the hammer at every start and stop.
If a system bangs every time the pump kicks in, do not just tighten the pipes. Fix the spike, or you will be fixing joints forever.