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Thread: Machine-gun water hammer

  1. #1
    DIY Junior Member linty's Avatar
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    Default Machine-gun water hammer

    My water hammer sounds like a machine gun that bangs in the pipes at a frequency of about 3 or 4 times a second and the episode lasts about 20 seconds. It can be triggered by shutting off a faucet or sometimes it seems to start spontaneously. After an episode of hammering, nothing will cause it to happen again for at least 10 or 15 minutes. It bangs from one end of the house to the other so I can't pinpoint the cause. There are hammer arresters on the washing machine. Any ideas on why this is happening?

  2. #2
    DIY Senior Member kreemoweet's Avatar
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    Why? Perhaps a chattering automatic valve of some kind. You can test for this by shutting off suspected appliances one by one to see if the hammering stops.
    Another big cause is unsecured pipes. That's a tough one, because you'd need to isolated the area and then open walls to fix it. Leaky toilets are very
    likely the cause of hammer occuring when "nothing" is running.

  3. #3
    DIYer, not in the trades LLigetfa's Avatar
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    It could also be a bad PRV.

    Are you sure you are not exaggerating it. That is between 60 and 80 bangs, which is quite a lot.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    What is the water pressure in the house? A toilet fill valve that is chattering (possible with high pressure) could cause this. I'd turn the water off to the toilet(s) and see if the level in the tank drops, indicating a flapper valve leak. This can cause asynchronous partial fills. Also make sure that all of the shutoff valves are fully open. A loose washer in a shutoff can cause chattering, but only when there's water flow.

    If you have a PRV and a failed expansion tank (or none), as already called out can cause noises. Some PRVs have a bypass valve that could make that noise, too, but it should normally never open unless you have a failed expansion tank (or none). Double-check that the T&P on the water heater is not discharging.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    In the Trades dwindle's Avatar
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    Is there possibly a mixing valve somewhere?

  6. #6
    DIY Junior Member linty's Avatar
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    The expansion tank was replaced just a couple years ago so I don't think that's failed. Already replaced the PRV so ruled that out. Most of the shut-offs are ball valves. Don't know the house pressure since there's no gauge.

    Quote Originally Posted by jadnashua View Post
    What is the water pressure in the house? A toilet fill valve that is chattering (possible with high pressure) could cause this. I'd turn the water off to the toilet(s) and see if the level in the tank drops, indicating a flapper valve leak. This can cause asynchronous partial fills. Also make sure that all of the shutoff valves are fully open. A loose washer in a shutoff can cause chattering, but only when there's water flow.

    If you have a PRV and a failed expansion tank (or none), as already called out can cause noises. Some PRVs have a bypass valve that could make that noise, too, but it should normally never open unless you have a failed expansion tank (or none). Double-check that the T&P on the water heater is not discharging.

  7. #7
    DIY Junior Member linty's Avatar
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    The boiler has a tankless coil that goes to a mixing valve before the hot water gets to the rest of the house. Why do you ask?

    Quote Originally Posted by dwindle View Post
    Is there possibly a mixing valve somewhere?

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    Expansion tanks generally last more than a few years, but it's possible...knock on it...if it sounds a dull thud, it's toast. If it sort of rings, it should be okay.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #9
    Forum Admin, Expert Plumber Terry's Avatar
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    Things that may require a hammer arrestor
    Dishwasher
    Clothes washer
    Icemaker

    Anything with a solenoid shutoff

    If you have a refilling toilet tank, and a bad fill valve or wall shutoff
    Make sure the wall shutoffs are open all the way. A floppy washer will hammer.

  10. #10
    DIY Junior Member linty's Avatar
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    Thanks for all your advice. Finally narrowed it down to the leaky tank flapper valve and the pulsating fill valve on my Toto Drake toilet.

    Quote Originally Posted by linty View Post
    The boiler has a tankless coil that goes to a mixing valve before the hot water gets to the rest of the house. Why do you ask?
    Quote Originally Posted by Terry View Post
    Things that may require a hammer arrestor
    Dishwasher
    Clothes washer
    Icemaker

    Anything with a solenoid shutoff

    If you have a refilling toilet tank, and a bad fill valve or wall shutoff
    Make sure the wall shutoffs are open all the way. A floppy washer will hammer.

  11. #11
    DIY Junior Member Leif Ernstsen's Avatar
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    Default Machine-gun-like noise from cupper piping

    Hi,

    I want to share the following experience with you:
    I have a cupper pipe water installation in the house. The supply water to the house is pressure reduced to 4 bars (~60 psi). Some time ago I experienced a violent machine-gun-like sound, when a hot water faucet was opened fully. It obviously would continue as long as the faucet was held open, but I never tested this; the noise was so severe that I was afraid of damage to the piping and therefore closed the water off as soon as possible. I experimented a little with respect to how this special noise was triggered. At low flow (from the hot faucet) there was no problem, but as the flow was gradually increased, a high pitch singing tone was heard, which eventually swopped into the "machine gun" loud bangs, I guess around 5 bangs per second. After some trouble shooting involving blocking off various appliances, it was found that the bangs were related to the washing machine being located in the neighbor room some meters away. When the water supply to the washing machine was switched off via the ball valve at the wall, then no bangs appeared. But when this ball valve was opened, and the washing machine was not in use, then the bangs were back. So I think the cause is the solenoid valve in the washing machine. I have to mention that this is a washing machine (Siemens) with only one water supply line (cold); the water is being heated inside the machine. Here in retrospect I can see that the problem arose after we had this new Siemens washing machine installed.

    This is the present status. I will check with the washing machine dealer, if he is familiar with this problem, and how he would advise to solve it. Also I am considering installing a water hammer arrestor at the water supply line to the washing machine. Does anybody have an opinion, if this will help?

    Any comments will be appreciated.

    Regards,
    Leif Ernstsen

  12. #12
    DIY Junior Member Leif Ernstsen's Avatar
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    Hi, here comes an update per 1. April 2014:

    I was at the dealer on Saturday, but the support department was closed this day. I could try again after the wekend. Well, I then took a closer look at the problem at home. There appeared to have been a small leak below the valve at the wall, as there was a small wet-looking area on the floor below it, maybe with an area as a circle with diameter 10 cm. However, the wet surface was not water-wet, but rather a little sticky, as if oil or soap had been involved. I then disconnected the water supply hose to the washing machine. It was not very firmly tightened. I took out the strainer, which had a rubber seal ring at the circumference. All looked clean, but the rubber seal had been squeezed so that it had a few rubber threads 1-2 millimeter long ends protraining. I cut off these threads and assembled the whole thing back. Here, by the way, I discovered that the valve does not look like a ball valve, it is rather a cock-type valve. When testing, the machine gun sound does not appear any more. However, the high singing pitch tone is still there, but only when the hot water faucet is opened fully. With this I consider the problem solved. I am just amazed that the system is so sensitive to such small details.

    Regards,
    Leif Ernstsen

  13. #13
    Moderator & Master Plumber hj's Avatar
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    "Water hammer" is basically an "instantaneous" single event, NOT a "machine gun chatter". What you are describing is a toilet with a bad fill valve AND a leaking flapper. The fill valve chatters when it closes, and the leaking flapper makes it recycle on a repeating basis.
    Licensed residential and commercial plumber

  14. #14
    DIY Junior Member Leif Ernstsen's Avatar
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    Hi hj,
    Thanks for the info. Will keep it in mind, if the machine gun starts again.
    Leif

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