A Simple Cure for Water Hammer
Here's a way to add a water-hammer arrestor to your washing machine water lines without cutting any plumbing lines.
I recently changed the water hoses on my clothes washer from the all-rubber type to a new style with a braided-metal covering. The next time I used the washer, a loud bang resounded when the water turned off.
The all-rubber hose was much more expandable than the metal type. Because it’s more expandable, the rubber type dampened the pressure surges causing water hammer. Luckily, I’ve figured out how to fix water hammer by making an arrestor out of a few simple items.
First, I went to the hardware store and bought a couple of water-hammer dampers, 4-in. lengths of copper tubing closed at one end and threaded on the other. Inside, an air chamber dampens pressure surges. The instructions said to cut into the copper water lines and to solder in T-fittings to mount the dampers. I figured out a way to avoid that step.
At each faucet, I installed Y-hose fittings. Next, I attached a female hose thread to a female pipe-thread coupling on each Y-fitting, followed by a water-hammer damper threaded into each coupling. This solved the problem. The copper tubes will likely fill with water over time. When that happens, I’ll unthread them, pour out the water, and reinstall them.
— Robert Tata; Huron, OH
From Fine Homebuilding #216
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The problem I've found with the Y hose fittings is they have a reduced outlet size so the washer will fill slower.
Isn't the water hammer stub supposed to point up?
Hi Robert, Copper tube is a good idea as long as it points upward for a functionning air damper. As shown will instantly fill up with incompressible water and be useless...
You can keep your "Y" fitting if you add a 90d elbow between it and your copper tube. The later will point to 45d upward, maintaining the required air damper.
Air chamber must point upward to work, pointing down as shown instant failure.
Another thing to consider on water hammer is always turn the water supply on or off slowly, and it's even better to do so with an outlet open like a tap, so pressure has an escape.
The braided stainless hose you're using gives a false sense of security. If you look at the inside it's simply a rubber hose. The braided portion is for outside protection, hardly necessary for automatic washers, and certainly not necessary for all the garbage you have for water hammer that's not installed properly as shown, and won't work without a lot of unnecessary maintenance. Stick with good quality auto washer hoses, they'll last for many years, much longer than braided hose.