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Thread: Pipes bang hard when cold water on full blast

  1. #1
    DIY Junior Member Carri's Avatar
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    Default Pipes bang hard when cold water on full blast

    This did not happen prior to our bathroom remodel. Only after our bathroom was redone did the pipes start banging when the cold was on full blast, but this only happened at the kitchen sink. The banging did not happen when you turned the water off. It was when the cold water at the kitchen sink was on full blast that it happened. The remodeled bathroom is on the second floor, not above the kitchen, and if you turned the cold on full blast at the kitchen sink, the pipes in the kitchen started banging really badly.

    So we got in touch with the contractor who redid the bathroom, and his plumber did not know why the banging was happening. He tried to remove air from the pipes but that did not solve the problem. Next he installed a vertical piece of pipe in the upstairs bathroom under the sink (picture one attached) but this also did not solve the problem. Now tonight he installed a different type of vertical piece of pipe in the kitchen under the sink (picture two) and this seems to have stopped the horrendous banging.

    It seems that these vertical pipe pieces (on the cold lines only) are a patch to the problem, which was not a problem before the bathroom remodel. Our plumber seems to want to blame our new Jado valve, saying that it causes too much pressure in the lines. We want to know why this banging happened in the first place (only the cold full blast in the kitchen) and whether these vertical pipe pieces make any sense. We do not want to have to drain the lines periodically so this alleged patch job continues to work.

    PSI is 65. Thoughts please? Thanks in advance.

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  2. #2
    DIY Senior Member dlarrivee's Avatar
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    The first chunk of copper is useless, the second is a proper water hammer arrestor.

    What happens if you regulate the pressure down to 50psi instead of 65?

  3. #3
    DIY Junior Member Carri's Avatar
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    Not sure how to change the PSI to 50 but if you turn on the outside garden hose and cold at the kitchen sink, the kitchen pipe banging seemed to stop. The thing is though that PSI 65 did not bang any pipes prior to the bathroom remodel.

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    Master Plumber Redwood's Avatar
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    There is either debris in the pipes or a loose washer on a valve somewhere...

  5. #5
    DIY Junior Member Carri's Avatar
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    Thank you for the replies. Four more questions please...

    Do you think it is possible to fix the pipe banging without the use of these vertical pipe pieces?

    If the upstairs vertical pipe piece is useless (picture one in first post) should it be removed?

    If these vertical pipe pieces stay in place, will we need to drain the lines periodically to prevent the banging from coming back?

    Could the pipe banging have been prevented in the first place?

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    A hammer arrester is an engineered device with a sealed air chamber (a piston or bladder - yours has a piston separating the air and water). It works until it fails, and that should take many, many years. The first one is an old school air chamber...open to the water, and very quickly all that air will disolve into the water stream as it passes, and be useless. Shutting and draining the lines usually won't restore the air (think finger over the top of a straw). SO, shortly, it will be come useless. It could stay, but it isn't doing anything.

    Water hammer is caused by moving water stopping rapidly, causing the pipe to continue to move via inertia until it hits something, like a hammer, and you hear the noise. A constant vibration is usually caused by either some debris bouncing in the pipe against something that is then restricting the flow, and the pipe then vibrates. As noted, if there is a valve with a loose washer, that washer can vibrate as water passes, changing the water flow, similar to some debris. You may have to remove the aereators from the faucets, maybe the cartridges, and the toilet fill valve then turn the water on to see if you can dislodge any debris.

    Make sure all shutoffs are fully opened, and if not 1/4-turn ball valves, you might want to consider changing them to that type (1/4-turn valves don't have traditional washers and have less restriction).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    Master Plumber Redwood's Avatar
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    Quote Originally Posted by Carri View Post
    Thank you for the replies. Four more questions please...

    Do you think it is possible to fix the pipe banging without the use of these vertical pipe pieces?

    If the upstairs vertical pipe piece is useless (picture one in first post) should it be removed?

    If these vertical pipe pieces stay in place, will we need to drain the lines periodically to prevent the banging from coming back?

    Could the pipe banging have been prevented in the first place?
    yes, it doesn't matter, no because it hasn't solved the problem, probably not

  8. #8
    Moderator & Master Plumber hj's Avatar
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    The real problem that what you describe is NOT conventional water hammer which occurs ONLY when a faucet or valve is closed suddenly. It does not happen while water is flowing, so we cannot tell what the cause was, or why the arrestor "cured" it.

  9. #9
    DIY Junior Member VernK's Avatar
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    The arrestor, in this case, added a "spring" to the system and maybe luck just had it that it was just the right rate to damp the vibration

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    Homeowner Thatguy's Avatar
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    If the arrestor works under all conditions can we say logically say that there are pressure waves in the system?
    Regarding "full blast", turbulence must increase with fluid velocity, right?

    Was the banging once per second, 5x per second. . .?
    Are the pipes clamped at the recommended intervals?
    Last edited by Thatguy; 10-16-2010 at 06:46 PM.

  11. #11
    George the Plumber Gsalet's Avatar
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    Don't forget about pressure balance shower valves with check stops, If debris gets in the stops it will cause the pipes to bang when anything is turned on randomly.

  12. #12
    Homeowner Thatguy's Avatar
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    So if the problem were debris the noise would have stopped anyway if the plumber just waited.

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    Moderator & Master Plumber hj's Avatar
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    Debris is the least likely source of the noise and would have been evacuated as soon as the water was turned on and the faucets used, anyway.

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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by Thatguy View Post
    So if the problem were debris the noise would have stopped anyway if the plumber just waited.
    Well it would stop if the debris/loose washer was flushed out or, removed...
    Right now the arrestor is dampening the pulsations that are still there or, the debris moved to where it is not a problem at the moment.

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    Homeowner Thatguy's Avatar
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    I guess the next logical step is to buy a pressure gauge for a few bucks and see what it says.

    Also try turning off the water using a washing machine, which valves work very fast, and see if that brings back the banging.

    Try as many different ways as you can to bring back the problem so as to provide troubleshooting clues.
    Or hope that the problem never returns. Hoping is free, even in this economy.

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