I have water hammer arresters for my washing machine like in the image.

The pressure at my place is about 83 PSI (no pressure reducing valve, no expansion tank, no check valve in the main). These arresters were installed by the previous owner, probably 7 years ago.

The washing machine makes a very loud banging when in use. The only way that I have found to work around the issue is to open the valves just a little bit (it is like 90% closed).

I wonder if it is that the water arresters are damaged and need to be replaced. If so, how to replace them? Am I supposed to replace the whole plastic box, or can I replace individual arresters? There doesn't seem to be enough clearance in the box to unscrew the arresters and get new ones in.

Water hammer arresters

2 Answers 2


Those are arresters with threaded connection and they are replaceable. Check your plumbing supplier.

You might need to remove the valves from the box in order to replace the arresters. I'm not sure the box is tall enough to take them out while leaving the valves in place. Sioux Chief makes a few other boxes like this that are taller; might be why.

  • 2
    Usually the box flexes enough to get them out. I would ask the previous owners if you can if those did much good. They are fairly small but having 2 I would expect them to do the job.
    – Ed Beal
    Nov 6, 2020 at 0:24
  • 1
    @EdBeal: I think the previous owners didn't care much. I asked them about the banging and they were like "yeah... it happens somethings, we don't know". Also, the city redid the street supply a few years ago, which increased pressure, I am not sure about the timeline (I think the arresters are older than the city rebuild). I am thinking I will leave these ones in place and install another one in the washing machine inlets.
    – rufo
    Nov 6, 2020 at 14:10

A water-hammer arrester is an (initially) air-filled container that simply acts as a compressible "shock absorber". Over time, the air can dissolve in water and be lost, particularly on older models without pistons, leaving it filled with pretty-much incompressible water. They're easily fixed or replaced.

If the existing arrester has replaceable O-rings:

  1. Close the main interior shutoff valve.
  2. Turn on faucets in the lowest floors to help drain the system.
  3. Get some buckets and towels to soak up water, and place below the arresters.
  4. Unscrew the arresters, disassemble them to drain the water, and check for damaged O-rings.
  5. The O-rings can be replaced at very low cost. If possible, find the right size O-rings in advance or get an inexpensive assortment to shorten the downtime.
  6. Reassemble, turn on the main shutoff and test the system.

If the O-rings cannot be replaced, by design:

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