Water hammer
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Thread: Water hammer

  1. #1
    Join Date
    Dec 2008
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    Ontario Canada
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    Water hammer

    I'll start by saying I'm not a plumber and I do very little plumbing. I do lots of hydronic heat, HVAC and ref work, but try to stay away from plumbing, I need some help with water hammer.

    Replaced a tank for a friend (of course). Removed a natural draft tank located in centre of house, and installed powervented tank 6' away on outside wall. Changed no other plumbing, 3/4 in and out of tank.

    Before install, no water hammer (I know this as I lived there a while). After install crazy bad water hammer on ALL fixtures, hot AND cold, even when the toilet shuts off! Tried installing 2 of those little Oatey water hammer arresters in both the hot and cold mains, as high as possible and close to tank, did little to suppress the problem.

    With tank valves shut off, no water hammer at all. With air pockets in the lines, the hammer goes away, but once all the fixtures are are operated, and the air is gone, it's back.

    I know I could put a bigger shock arrester in and likely stop the noise, but I really want to FIX the problem

    I'm at a loss, any suggestions?

    The tank is not %100 level, but its fairly close, could that effect it?

  2. #2
    Join Date
    Mar 2011
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    How many BTU's does the heater require. How many gallon's are in the tank. How many fixtures are in the house. What size expansion tank did you install. What type of faucets are in the house and are there any old fixtures with washers for valve shut off. How about single handle faucets. Do you have a pressure regulator. And finally what is the water pressure.

  3. #3
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    Have you tried draining the entire system then refilling slowly?

  4. #4
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    Around 20,000 BTUH I think. I will double check
    60 gal
    1 single valve kitchen sink
    Dishwasher
    2 valve bathroom sink
    2 valve shower
    Washing machine
    2 toilets
    Water pressure is 40-60 psi ish (have to put valve on to check)
    I should note, hammer is delayed after shutting off faucet. Close sink, count 1, 2, BANG

    Arresters are just little guys (the kind you buy at Home Depot) about the size of a roll of quarters. I'll do some research and grab more info

  5. #5
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    Quote Originally Posted by AccurateHT View Post
    Have you tried draining the entire system then refilling slowly?
    No, what would that do?

  6. #6
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    Morgan Hill Ca.
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    Just a stupid thought...


    Did you check to make sure the dip tube was on the correct side? Or there at all? should be on the "cold side".
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  7. #7
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    What about the expansion tank. It is usually a code requirement. And what brand of water pressure regulator do you have installed and what is the model number.

    Also check that all the washer's in the fixtures are in good condition. I have seen many times where they are old and not seated correctly which will cause this symptom.

  8. #8
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    Jul 2007
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    Quote Originally Posted by LKJoel View Post
    No, what would that do?
    May not make a difference but if fast fill is displacing water in an important air stub a slow fill will correct it.

  9. #9
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    Dec 2008
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    Did not verify dip tube, good suggestion

    All houses here run off of city pressure and don't have reducing valves. I lived here 3 years, never so much as a tap. Now, it's really loud.

    All fixtures are low flow. This is a small war time house. 1200 ftsq. nothing extravagant here at all

    Next step for me is to remove valves from tank, check dip tube, install bypass between hot and cold lines with shutoff between and preform more tests to see if its the tank or house

  10. #10
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    Quote Originally Posted by AccurateHT View Post
    May not make a difference but if fast fill is displacing water in an important air stub a slow fill will correct it.
    Possible, I helped him do a lot of plumbing changes before the tank changeout. So maybe not, but will play around

  11. #11
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    I would isolate all the faucets and toilets and see if that makes a difference.

  12. #12
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    Quote Originally Posted by alcomech View Post
    I would isolate all the faucets and toilets and see if that makes a difference.
    You mean isolate and test 1 by 1?

  13. #13
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    Turn off as many fixtures at there shut offs located under the sinks, cabinets, etc. and see if there is a fixture in particulate which is suspect.

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