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Water Hammer Question

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  • Water Hammer Question

    What is the best way to fix water hammer in a residential system? I have seen an 8" or so 'fitting' that is designed to cure water hammer but is it better than using a capped 12" verticle length of pipe? Where is the best place to put either device? Can it go at the water heater (hot or cold or both?) or is it best to use a few say at each sink. Suggestions appreciated

  • #2
    I'm not a plumber, but I make my own with 3/4" capped tubing. These do not meet code requirements in my area (the simple manufactured one don't either). Inspectors don't care if you add them though as long as you have the code approved units on fast acting valves (washing machine and dishwasher). The code approved units are the terribly expensive ones with a small bladder inside.

    I believe the theory is that with open chambers all the air will eventually diffuse into the water leaving no air cushion. This is probably true, but it will take quite a while. I figure if noise develops you can always drain the system and recharge your homemade air chambers. All the plumbing I've done this way is completely quiet.

    Also, when sizing these things, remember that with 60 psi water and 15 psi static air pressure, only 20% of the volume in the chamber will be air. That's one area where the bladder type units excel. They can be pre-charged and maintain a larger percentage of the volume for air cushion.


    • #3
      ByteButcher is correct. Before the manufactured shock arrestors were available it was a common fix to 'build-your-own'. He is also right in that they will eventually water-log and while reaching that point their effectiveness will dwindle. THe way around that is to install two valves at the chamber, one so you can isolate it from the sstem and the other to drain the water out. This avoids having to shut down the entire system and draining it, much easier and more likely to happen on a regular basis with the valves installed. BTW, use ball valves. Install as close to the source of the problem (usually a washing machine or other equipment that has a solinoid controlled water supply) as possible and/or at the end of long runs of pipe. So if you have a main that runs through your house and all your branch lines TEE-ed off of it you can probably get away with one at the end of the line. As a minimum use the next size pipe larger than your main, so a 3/4" main the chamber should be 1" and about 12" tall is a good height for this size. There is a formula but I don't remember it. Chamber needs to be mounted vertically, the commerical pre-charged ones are not sesistive to orientation but still are better of if mounted vertically and should also have one isolation valve so they can be changed out because that disphragm inside does not last forever.


      • #4
        All commercial and residential plumbing in my area is done using self-made air chambers, and it's all code.
        As an example, if you are running a couple risers up to feed two angle stop valves for a sink, we normally sweat in a tee just below where the stops will be fitted and run a "to fit" 90 in the tee and a 12" vertical run of capped copper into that, then continue running the riser up from the top of the tee to the angle stop. Same with toilets, shower manifolds, etc. No need to buy the pre-manufactured air chambers, the DIY ones work and do the exact same thing.

        [ 05-22-2004, 01:40 PM: Message edited by: David M. ]


        • #5
          1 more thought...beware of side-by-side dual sinks like in some bathroom vanities. They are the most frequent causes of water hammers because only one sink is cushioned.


          • #6
            A "side by side" dual sink bath setup like you describe should'nt cause any more water hammer than a single faucet if plumbed correctly. If there are 4 angle stops feeding both sinks (an angle stop for each hot/cold side on both) then installing a air chamber on each line should cure the problem. If only 2 valves are feeding both sinks, as long as an air chamber is on each cold/hot angle stop then it still should'nt be an issue as long as the runs feeding the second sink are straight with minimal 90's or bends (using a tee to branch off with).


            • #7
              I think that the automatic equipment, as the diswashes,washing machines; are the most important to protect with air chambers. A well holded of the pipes, resolves an important part of the problem. I think thus.