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Our washing machine had to be replaced, and after the new machine was installed, there's significant water-hammer in the copper plumbing of our house, which was built around 1950, when the machine's fill valves close.

There are water-hammer arresters (cylinder-type with a piston inside) on the supply lines immediately adjacent to the washer, just a couple of feet, standing between it and the hot and cold supply lines with no other pipe intersections/branches in-between. There was no water hammer issue with the old machine.

To be sure the arresters haven't worn out or that the pistons hadn't gotten stuck, I replaced them with new ones the same size as the old ones, but without any improvement. So I'm not sure what the troubleshooting next steps should be. Advice?

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    Do you have access to the piping? If it isn't the hammer arrestor, next on my list of things to look at would be how the pipe is strapped to the framing. Nov 24, 2023 at 15:45
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    Check your water pressure. Pressure regulation is a potential solution.
    – popham
    Nov 24, 2023 at 20:06
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    I placed a small bladder pressure tank in my cold water line and the problems are gone, been working for about 15 years. At the time they were not very expensive.
    – Gil
    Nov 24, 2023 at 22:18
  • @Gil: When you say "small", do you mean one of the really small ones, about the size of a grapefruit? I've found a stainless steel one that is NSF61 compliant for about $60.
    – mr blint
    Nov 27, 2023 at 15:36
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    @popham: Pressure is 80psi.
    – mr blint
    Nov 27, 2023 at 15:38

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Your new arresters may be defective (a common thing in my experience). The flow rate of the fill valves on your new washer may be significantly greater than the old ones, and require larger (or more) arresters to be effective. You could try throttling down the flow with the shutoff valves to see if that reduces hammering.

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    If throttling down the valves works for you but you habitually turn off the valves when the washer is not in use, you can get flow restrictors designed for garden hose connections so you don't have to fiddle with the valve setting every time you use the washer. Some restrictors replace the rubber washer in the female end of the hose and have a reduced size hole instead of a full bore.
    – MTA
    Nov 24, 2023 at 17:04

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