How to Quiet a Noisy Dishwasher
Richard Trethewey suggests the solution to banging dishwasher pipes
We have a problem with pipes banging whenever I run the dishwasher. The plumber installed what he called an arrestor, but it’s just a short, capped pipe that sticks up from one of the horizontal pipes. It doesn’t seem to help. Is there a way to stop the banging? —Gloria Long, Mercer, PA
You have a classic case of water hammer, which happens when a valve, like the one in your dishwasher, quickly shuts down water flow. That sudden stoppage temporarily causes a big local spike in water pressure, which then dissipates throughout the plumbing system, resulting in loud thunks and rattles as it shakes loose pipes. Besides being annoying, all that shaking and banging is not a good thing for the joints or the fittings.
Plumbers used to—and apparently still do—make their own water-hammer arrestors in the field by attaching a short, capped pipe to an upright T-fitting on the offending pipe, just as your plumber did. The idea was to capture a slug of air that would cushion the shock when the valve is shut. It actually works—for a while—but eventually the capped pipe fills with water and no longer absorbs the shocks.
Here’s a better solution: Install a water-hammer arrestor with an internal diaphragm that keeps the water and air in separate chambers. The compact Mini-Trol arrestor (AMTROL) works well for most residential applications.
Have your plumber install one as close as possible to the source of the hammering—the hot-water line to your dishwasher. Then have him secure any pipes that the hammering may have loosened. That simple fix should restore peace and quiet to your plumbing system.