Water Hammer Arrestors Explained
Introduction
If you hear loud banging, knocking, or thudding when you shut off a faucet or when appliances stop drawing water, your plumbing system is likely experiencing water hammer. While the noise can be startling, the real concern comes from the stress these pressure surges place on pipes, valves, and fixtures. Over time, repeated water hammer can cause leaks, joint failures, and costly plumbing repairs.
What Causes Water Hammer
Water hammer happens when moving water stops suddenly. Because water carries momentum, a fast closing valve forces that energy to stop instantly. With nowhere to go, the pressure surges back through the pipes. This sudden force creates a pressure wave that makes pipes vibrate or bang against framing and other surfaces.
Modern appliances such as washing machines, dishwashers, and ice makers commonly trigger water hammer because they use solenoid valves that shut off instantly. Homes with high water pressure experience these problems more frequently because increased pressure intensifies the shock.
What Is a Water Hammer Arrestor
A water hammer arrestor is a plumbing device that absorbs sudden pressure changes. Inside the arrestor, a sealed chamber holds air or gas separated from water by a piston or diaphragm. When water flow stops abruptly, the excess pressure moves into this chamber. The chamber cushions the shock and prevents it from slamming into the pipes.
Unlike older air chambers, modern arrestors use sealed designs that maintain their effectiveness over time.
Where Water Hammer Arrestors Are Installed
Plumbers typically install arrestors close to the fixture or appliance causing the problem. Common locations include behind washing machines, under sinks for dishwashers, near refrigerator ice makers, and at shutoff valves for toilets and faucets. Correct placement plays a critical role in how well the arrestor protects the plumbing system.
Benefits of Installing a Water Hammer Arrestor
Installing a water hammer arrestor reduces noise, protects pipe joints, and extends the life of appliances and fixtures. It also helps prevent long term damage from repeated pressure stress, which can weaken pipes and cause hidden leaks behind walls or ceilings.
When to Call a Professional
Some homeowners install water hammer arrestors themselves, but correct sizing and placement matter. A licensed plumber can evaluate your plumbing system, measure water pressure, and install the proper arrestors to fully resolve the issue and prevent future damage.
