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I've got a 1953 single-story house, with all copper water piping. When turning on the shower upstairs, there is frequently some serious water hammer. I'm familiar with water hammer that goes "bang" once when opening or closing a valve, but this makes a extremely loud, repetitive banging, sort of like a machine gun or jackhammer. It usually doesn't stop until the valve is fully opened.

The shower has two separate hot and cold valves, and they open fairly slowly (I think they're gate valves). What might be causing this, and how can I fix it? It is pretty severe, and it sounds like it will cause damage sooner or later.

EDIT: ok, so after some research, it looks like this "jackhammer" water hammer is pretty common, but I still don't know what causes it... I'd love to understand better.

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    Probably there is a pipe that is not strapped and it’s vibrating due to turbulence in the water as the valve is opened. The pipe is hitting framing I’d guess.
    – RibaldEddie
    Jan 31, 2022 at 1:31

2 Answers 2

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A few things can help ameliorate water hammer:

  1. If the problem occurs particularly on one faucet, it's likely a loose washer causing vibration, either in the faucet valve or in the shut-off valve under the sink. Take apart the faucet and shut-off valves and replace washers and the screws holding them.
  2. Loose pipe mounting brackets exacerbate the banging. Tighten existing brackets, and possibly add a few more.
  3. Air chambers can reduce or eliminate water hammer. There may be an existing air chamber that has lost its captive air. It can be drained (i.e., refilled with air), but it also can be replaced with an air chamber with a bladder that prevents air absorption.
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    1953 - try shutting off the water, opening all the taps, and draining form the lowest available drain in the system - odds are that if there are hammer arrestors in place, they are plain pipe stubs, and this would get them air. Expect some rust when you turn the water back on (even with copper pipes.)
    – Ecnerwal
    Jan 31, 2022 at 1:51
  • @Ecnerwal sounds like an answer to me.
    – FreeMan
    Jan 31, 2022 at 14:17
  • Nope, just a comment on this answer that already includes them.
    – Ecnerwal
    Jan 31, 2022 at 14:50
  • Appears it's item 1. I've had the water off a dozen times for other plumbing stuff, and I haven't seen any air chambers. Besides, items 2 & 3 wouldn't account for the continuous nature of this hammering. It'll have to wait until I gut the upstairs bathroom to find out for sure, since I don't want to break into the tile wall to get at the valve in question until then.
    – mister-sir
    Jan 3 at 0:20
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Check the plumbing vent in the attic. A plumbing vent is a plastic pipe that ties into the sewer pipe so a vacuum can't form, stopping the flow of water from going down. See if the pipe supports came loose. That would bang I believe.

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  • This was already mentioned in point #2 of the other answer. However, since water doesn't flow through the vent piping (in most cases, especially not the piping in the attic), it's unlikely that a loose vent pipe would cause banging. Unless the actual vent through the roof is blowing in the wind.
    – FreeMan
    Jul 11 at 18:10
  • #2 in not about the plumbing vent in the attic. I had the firewall repair done and the pipes started banging in one of my bathrooms wall thereafter. The repairman came back and checked the plumbing vent in the attic. Not sure what he had done, but the banging stopped.
    – Valeria Myromzeva
    Jul 11 at 21:44
  • Edit: #2 is not about the plumbing vent in the attic- it is about the pipes in the wall. I had the firewall repair done and after that the pipes started banging/thrashing violently in one of my bathrooms wall. I thought it could shake the pipes loose at their joints and cause leaks. The repairman came back and checked the plumbing vent in the attic. Not sure what he had done, but the banging stopped. Yes, it does look there is no connection, yet, after consulting with a structural engineer, it was suggested to check the plumbing vent in the attic.
    – Valeria Myromzeva
    Jul 11 at 21:57

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