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Plumbing – Water Hammer Solution?

gtoguy | Posted in General Discussion on December 7, 2005 07:09am

OK – some serious hammering has started near my hot water heater. When I close the valve just upstream of the tank, it stops. If I install a “Water Heater expansion tank” (manufactured by Watts) upstream of the tank, should this fix the problem? I already tried one of those small “upside-down brass test tube” hammer arrestors near my washing machine. It didn’t fix the problem.

It looks simple – just sweat a female fitting upstream of the cold water in side on the HWH – then screw the thing up into it. Any expert knowledge out there on the issue? Thanks in advance.

Tim


Edited 12/7/2005 2:38 pm ET by GTOGuy

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  1. WorkshopJon | Dec 07, 2005 07:14pm | #1

    GTO,

    (used to have a couple, years ago) Have you tried draining your pipes to recharge the hammer arrestors?  Over time, they water log.

    WSJ

    1. JohnSprung | Dec 08, 2005 02:26am | #4

      In the olden days, we used to put in dry risers, just pieces of pipe sticking up with a cap on top.  When the system was filled,  some of the trapped air would compress into them.  That acted as a hammer arrestor.  Then after a while, the air would dissolve out into the water, and they'd stop working until you drained and re-filled the pipes.  Depending on size and usage, that might be a few months, or even years.

      Commercially made arrestors and expansion tanks have a rubber diaphragm that's supposed to protect the air from getting dissolved out.  If draining helps, either you have dry risers, or the diaphragm(s) are leaking.

      The arrestor needs to go near the valve that causes the problem.  The hammering happens because a lot of water is moving rapidly through the pipes, and shutting it off suddenly is sort of like a train in a tunnel hitting a brick wall.  The arrestor needs to be positioned to cushion the stop for most of that weight.   

       

      -- J.S.

       

  2. JTC1 | Dec 07, 2005 10:08pm | #2

    Ditto Workshopjon's post about draining pipes to recharge arrestors, don't know about the Watts tank, but it just sounds like an overgrown air chamber to me.

    I would also look at the anchoring of the pipes in the area where you hear the hammer.

    I was working on a guy's house fixing a few problems in prep for sale. Had a totally unanchored 12' run of 1/2" pipe in a crawlspace.  The run crossed the underside of several joists.  Every time the toilet in the rear bathroom shut off from a fill - it would bang.  5 minutes and a few pipe straps fixed (silenced) a nuisance problem they had lived with for the 22 years they had lived there.

    Does the hammer occur only when water is shut off suddenly? like a washing machine solenoid, dishwasher or toilet valve?  Or does it happen when the water heater is heating?  I used to have a gas water heater that would make a racket when heating - the cure was to drain the heater down to flush sludge / scale from the bottom of the tank - needed to be done about yearly.  New home with no scale problems now.

    Jim

    Never underestimate the value of a sharp pencil or good light.

  3. Shacko | Dec 08, 2005 12:57am | #3

    Is the valve you are closing a regular stop valve? if so that would be the first thing that I would look at. A loose or defective washer will make a hell of a noise. FYI a water heater expansion tank is not a hammer arrester, hammer arresters have to be near the problem. Hope Im helping and not confusing. Luck.

  4. User avater
    BillHartmann | Dec 08, 2005 05:17am | #5

    "OK - some serious hammering has started near my hot water heater. When I close the valve just upstream of the tank, it stops. "

    What hammer is a single bang, possilby followed by a couple of ratles, when water is suddely stopped.

    I think that you describing another problem. Something "loses" in the plumb is will alternately slow/stop the flow and then release allowing more flow. It can make a noise that sounds like a machine gun up to higher frequencies where it can sound like blowing across a pop bottle.

    The big difference is that it occures when water IS FLOWING and the rate will vary by the amount of water flowing.

    Most often this is caused by a loose/missing screw on the washer on a compression valve. But other things can cause it, such as said "missing screw" that moves in the line was the water flows to excess solder that has formed inside the pipe and moving around.

    1. gtoguy | Dec 08, 2005 05:49am | #6

      The sound has just recently started and it's continuous rattling - at an even freguency - within the pipes in the area of my hot water heater. If I open up a basin faucet, it goes away. Close it, it starts back up. I thought this is considered water hammer, but I'm really just a DIY knucklehead. The house is 23 years old. Our previous house (built in 2000) had an expansion tank (about the size of a basketball, filled with air/nitrogen separated from the supply by a rubber bladder) installed on the water line near the HWH. My understanding was that this was required by code in that city. Never a problem with that house. Thanks to all for advice.

      Tim

      1. User avater
        BillHartmann | Dec 08, 2005 06:13am | #7

        You need and expansion tank if you have a pressure reducer valve or a check valve/anti-shoyn valve on the line. Many cities are now installing check valves at the meters.What happens is that after you have used a lot of hot water the tank refills with cold water and the burner start heating it up. The cold water expands and it trys to push it back out the meter. If you have a check valve or PRV then the water can't "backup" and the pressure increases and cause the safety valve to release a little water.That is what the expansion tank is for.You don't have classic water hammer nor the noise that I described.Do you have a PRV? Water softener or whole house filter?Recently some one had a similar problem to your (IIRC it was in a different forum) and the noise turned out to be a defective PRV in the city lines. It was located just outside their home in the street.

      2. plumbbill | Dec 08, 2005 07:59am | #8

        You have Good advise from the other Bill

        & some other post too

        It does sound like you might have a loose or worn out washer in one of your valves which can act like a reed in a clarinet by someone who doesn't know how to play.

      3. WorkshopJon | Dec 09, 2005 12:36am | #9

        it's continuous rattling - at an even freguency "

        GTO,

        Had a similar thing happen to me.  Traced it down to a miss adjusted toilet bowl tank float of all things.  It would open and close (Vibrate) at a certain resonance, with the ripples in the tank amplifying the affect, and draining out the overflow.  Noise came from rattling pipes came from elsewhere though.

        WSJ

        1. gtoguy | Dec 09, 2005 08:21am | #10

          Thanks- I heard the noise today and it reminded me of the movie Caddyshack. Remember Chevy Chase's character blindfolded on the practice green? "NuhNuhNuhNuhNuh....." That's as best as I can describe it. The good advice I've heard so far leads me to believe it's a worn out valve on the water softener. The amateur troubleshooting continues...

  5. gtoguy | Jan 03, 2006 05:45am | #11

    Problem solved- We have an automatic water leveling device in the backyard pool. I shut off the valve to it and the hammering went away. The leveler is fashioned like a toilet float-valve. I guess the water getting much colder with the winter-time had something to do with the very-annoying machine-gun hammering. It didn't make any noise all summer. Thanks to those who offered help.

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