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Thread: air lock

  1. #1

    Question air lock

    After a shower or after the dishwasher or clothes washer run, I get a very rapid but fairly quiet hammering sound in the pipes. Running cold water from almost any outlet once or twice will stop the sound; but it comes back the next shower or wash.

    Any ideas as to cause and, more importantly, cure for this noise??

  2. #2
    Join Date
    Apr 2008
    Houston, TX

    Default Re: air lock

    I am really not exactly sure on this one, but a thought...

    You may need an expansion tank on your water heater. This is a small tank (about gallon sized) that installs inline with the plumbing just above the heater. It has a bladder inside filled with air. When an appliance uses the hot water, the water heater turns on to heat the water back up to the setting of the thermostat. Laws of physics tell us that when you heat water, it expands...thus ever so slightly expanding the pipes, but enough to allow them to rub against a joist or other support. When you open the cold water tap, you release that excess pressure in the system. Installing the expansion tank compensates for the, well, expansion. This could solve the problem, but you may need to consult with a plumber on this one.

  3. #3

    Default Re: air lock

    The water heater has an expansion tank. The noise seems mostly to be be in the cold water pipes, in that running cold water usually stops the noise.

  4. #4
    Join Date
    Feb 2008
    Nashville, TN

    Default Re: air lock

    i think you may to install a water hammer arrestor. It sounds as if air is coming in through the cold water lines and then causing the water lines to burp the air causing the sounds. This may or may not work, but I think if it is installed near the fixtures in question it may help. Process of elimanation. Good luck.

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