Water-hammer arrestor

A water-hammer arrestor is a small device with an air cushion (a sealed piston or chamber) that absorbs the pressure shock when flowing water is stopped suddenly, preventing the loud bang or knock in the pipes known as water hammer. The culprits are fast-acting valves: a washing machine or dishwasher solenoid snapping shut, a quick-close mixer, or a fast float valve — the moving column of water hits the closed valve like a hammer, and without somewhere for that energy to go it slams through the pipework. In Dubai the problem is amplified by high mains/pump pressure, which is why a pressure-reducing valve often helps too, but they solve different things: a PRV lowers the *steady* pressure, an arrestor absorbs the *sudden shock*. Beyond the annoying noise, repeated hammering loosens joints, stresses pipes and can crack fittings over time. The fix is to fit an arrestor close to the appliance or valve causing it (the washing-machine inlets are the usual spot). It's an inexpensive part that a good Al Ghubaiba's plumbing team can add where the banging originates. Valve makers such as Caleffi publish the arrestor and anti-hammer fittings used.