Water hammer combined with fluctuating pressure

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by kavehnj, Feb 20, 2013.

  1. kavehnj

    kavehnj New Member

    Feb 20, 2013
    Paris On Canada
    Hi Everyone,

    First timer to this forum. I have an issue in an upstairs bathroom, when the hot water is turned on there is banging in the pipes combined with a complete loss of water pressure which returns with a bang and then loses pressure again (and repeat).

    Will the installation of a water hammer arrestor neer the shower faucet cure my problem or is there some other thing(s) i should try 1st?

    Thanks in advance!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Water hammer is caused by moving water moving things when it stops abruptly (like when you shut off a fast acting valve - some toilet valves, ice makers, washing machines, etc. contain fast closing valves that typically cause water hammer). So, it doesn't sound like that's your problem. I will say that some brands of shower valves do call for arrestors to be installed.

    It sounds like you have a pressure balanced anti-scald valve and that there's some air in the lines. Normally, any air in the supply lines gets purged once you open a valve, and then isn't an issue any more. If you're on a well, you may have an issue with the pump injecting air or even some gas from the well itself. If you have a new water heater, sometimes the anode rod will react with the water to produce gas, and that is relieved when you use some hot water. In that case, you'd need to replace the anode with a different metal one that won't react (or treat your water).

    Do you get a spurt of air when you open any other hot water valves in the house?

    A pressure balanced shower valve requires the inlet pressure to be fairly even between the hot and cold supplies. If there's air on one side, it can slam the pressure balance spool valve and shut off both supplies until they become balanced again. The valve is just trying to do its job, and if it is really air, you need to address that first, then things should return to normal.
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  4. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Aug 9, 2009
    Sounds like a loose faucet washer. Is there a particular faucet that causes the hammer when being used? If so that would be the first place I would be looking for the loose washer.

  5. Jerome2877

    Jerome2877 In the Trades

    Aug 25, 2009
    Yep loose washer is my guess as well.
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