• Plumbpedia™ - How Does A Water Hammer Arrester Work?

Water hammering is caused by the quick shutoff of water supply lines. The energy in flowing water has to go somewhere, and when a valve is shut off, the pipes can flex and “hammer” against anything close--like nearby studs, joists or other water pipes. Solenoid-triggered valves, like the ones in dishwashers, washing machines and water softeners, shut off almost instantly, not only causing the most ferocious hammering but also putting strain on rubber hoses and copper sweat fittings. Hand-controlled faucets usually don’t cause as much hammering because the shutoff is more gradual. Water hammer arresters cure this condition with a cushion of air that absorbs the momentum.