Hydraulics & Pressure
Water Hammer
Water hammer is the pressure surge that travels back through a line when moving water is stopped or started too suddenly. Closing a valve fast turns the water's momentum into a damaging spike.
Water in a charged line has momentum. Shut a nozzle or a valve abruptly and that momentum has nowhere to go, so it converts to a sharp pressure wave that can hammer hose, couplings, appliances, and the pump.
The fix is technique, not math: open and close valves and nozzles smoothly. Slow operation lets the flow change gradually and keeps the surge from ever building.