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Thread: Water Hammer wont go away

  1. #1
    DIY Senior Member wallygater's Avatar
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    Default Water Hammer wont go away

    So far I have put two arresters on. (within 3 feet of the washing machine). One on the hot side and one on the cold side

    I then added a third one directly on the washing machine

    Brand new, LG, front loader.

    The hammer is coming from the cold feed into the coil on on boiler. all the way accross the room

    75 yr old, american standard, steam boiler, with an internal H/W coil

    It is the 3/4 copper cold feed that goes into that coil that is banging or the coil itself

    Would it be advisable to sweat in another arrester at that location??

    Does anyone think that it woud work? , before I go to all this trouble and expence.

    Also, wile I have the water off, and the pipe cut, Does anyone think it would be a good idea to insall two aresters at that location??

    This is a very loud, hard , bang. Directly at the coil location
    wally

  2. #2
    DIYer, not in the trades LLigetfa's Avatar
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    Theories abound on how water hammer works and how to mitigate it. Basically it is the inertia of mass as per Newton's three laws of motion.
    http://csep10.phys.utk.edu/astr161/l...wton3laws.html

    A 3 foot column of water after an arrester should not have much mass or inertia. Most arresters are placed at the wall stops which still have the supply hoses after it.

    If you have a very long run and if there are side branches off of it, the inertia could be reflected down the path of least resistance so additional stops on the ends of the branches may help. Hammer arresters normally have a fixed precharge that cannot be changed, so if you have unusually high pressure, that precharge may not be enough and the piston already be near the end of its range of motion. You might want to consider reducing the pressure or use small expansion tanks that can have their precharge adjusted.

  3. #3
    DIY Senior Member wallygater's Avatar
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    thank you for the replies

    I installed the aresters within 3 feet of the washing machine valves. they did nothing

    I then installed the (easy one with the threads), (made for washing machine connections), Directly onto the washing machine.

    It also did nothing to stop the hammer

    the hammer is coming from the cold water feed, to the DHW coil, in the boiler.

    about 12 to 14 feet worth of 1/2" and 3/4 " copper pipe away.

    the feed pipe into that coil is exactly where the noise is coming from

    there is a ball valve in the vicenity.

    it does not appear to be banging. it is definatly banging at the DHW coil

    Would another arrester work nest to that coil???

    would I be wasting my time ??

    is that coil banging the same way a valve in the system would be banging ?
    wally

  4. #4
    In the trades Dana's Avatar
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    What's your static water pressure when neigther hot or cold water is flowing anywhere in the house?

  5. #5
    DIY Senior Member wallygater's Avatar
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    Quote Originally Posted by Dana View Post
    What's your static water pressure when neigther hot or cold water is flowing anywhere in the house?
    I am sorry to say that I dont know. the last time I tested it was at the garden hose valve. at the time it was low. about 40 lbs i think
    wally

  6. #6
    DIY Senior Member wallygater's Avatar
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    this house has no exspantion tank. it has been poinnted out to me in the past

    we are here a very long time

    the plumbing works fine. we would hear an ocashinal pipe bang once in a while, but no big deal

    now that we have the new washer, its a problem

    i really think its the coil thats banging like i said

    i just dont want to go to all the trouble off cutting in and sweating another one of those hammer aressters if it wont work

    i plan to put it wihin 12 to 14 inches from that coil
    wally

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    Take a look at this short video http://www.youtube.com/watch?v=YgjRZq70GR4 ...the flowing water has energy (inertia). When the valve closes quick enough, it tries to keep going (conservation of energy). Instead of flowing through the now closed valve, it needs somewhere to go to dissipate that energy. This could be moving the pipe, or preferentially, moving the piston and compressing the trapped air in an engineered hammer arrestor. Most companies make various sized water hammer arrestors based on the size of the water pipe and the flow. You need enough 'space' inside the arrestor for it to absorb the amount of energy there...the bigger the pipe, the higher the pressure, and the quicker the valve closes, the bigger the arrestor needs to be. If your pipes are not anchored well, the arrestor will not be able to absorb all of the energy and the pipes will move as well. When it springs back, it can knock against something further away. SO, it's a two-pronged attack: anchor the piping AND provide a place for the energy to be dissipated (the arrestor - but it must be large enough).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    DIY Senior Member wallygater's Avatar
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    thanks. So far I have only seen one size arrester. it gets sweated onto 1/2" pipe

    I have 3/4 copper at that DHW coil. I agree that i could use a bigger one there

    can i install two of them at that location?? will that be the same as one big one ???
    wally

  9. #9
    Moderator valveman's Avatar
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    Many times the inlet size of the hammer arrestor is too small for the water to enter fast enough. For this reason I prefer a standpipe or a riser. This is simply a tee prior to the valve that closes, with a section of the same size pipe sticking up a couple of feet with a cap on the top. There is usually enough air in the water, which will rise to the top of the riser pipe. The air in the top of the riser is the cushion you need to stop the water hammer, and using the same size pipe has an opening large enough to catch the pressure wave.

    Another easy fix is to throttle the ball valve and reduce the flow rate and velocity filling the washing machine or toilet. They will fill slower, but this eliminates the water hammer when the valve shuts, as there is considerably less velocity.

    With the strong 60 PSI constant pressure in my house, I have to throttle the valve to all the toilets to stop the water hammer when the toilet float valve closes. The toilets fill a little slower, but not enough to make much difference.

  10. #10
    In the trades Dana's Avatar
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    Valveman wins the kewpie doll! Teed air-filled 3/4" pipe risers for water hammer arrestors at or near the water hose connections is probably going to be the right solution here. You need to be able to isolate it from the rest of the system so that you can drain it down with the hose valve should it ever become filled with water, but it should work just fine with 40psi static pressure.

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you don't want to continually be adding air to a riser pipe, seek out an appropriately sized arrester. Tests have proven that any air trapped in the riser will be absorbed by the water movement in fairly short order. Unless you have an air valve at the top and a compressor or pump, it rarely empties fully, and who wants to drain their system down on a regular basis? It just stirs up debris, clogs filters, aerators, check valves, etc., and often doesn't work...think finger over the end of a straw...the water, once it gets into a riser, doesn't like to come out! If your pipes are flopping around without support, you will likely need to anchor them, otherwise, none of the patch jobs you perform will work.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  12. #12
    Moderator valveman's Avatar
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    A bladder tank type arrestor will work, as long as it has the same size opening as the pipe. They are just a lot more expensive than a riser pipe. I don’t have trouble keeping air in my riser pipes. I think the air in the water finds the high spot (riser) when the flow stops, and keeps plenty in the riser. Kind of like air accumulating in the high spots of an irrigation line. I have more problems losing air through the Schrader or air valve in the top of the riser than anything. So I just glue on a good cap instead.

  13. #13
    DIY Senior Member wallygater's Avatar
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    ok thanks.

    I already have two hammer aresters installed directly before both the hot and cold supply lines to the washer

    i also have a third hammer arester installed directly on the cold inlet to the washing machine

    none of these three aresters have had any effect at all on th hammer

    my question is: will a fourth arrester work if i install it where the actual noise is comming from (the DHW coil, on the cold side.)
    wally

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    Okay, lets backup here. Water hammer occurs when the water is shut off, not during, or when the water is turned on. Is it actually ONLY making the noise when the WM turns off the water? Is it more than one bang? Does it happen EVERY time the WM turns the water off? Does it make noise if you set to only use cold, or only when hot is being used? Can you see the pipes moving when this occurs? Did you anchor anything? Unless you destroyed the arresters when you soldered them in, they generally solve the problem IF it is truly a WM related water hammer. It's hard to diagnose without being there.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  15. #15
    Moderator valveman's Avatar
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    Did you try reducing the flow with the faucet? Make the WM fill slower and you won't hear the hammer on valve close.

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