Air chamber--drop elbow vs drop tee?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Neptune, Nov 3, 2012.

  1. Neptune

    Neptune New Member

    Messages:
    5
    Location:
    Illinois
    Why does it seem customary to install an air chamber as a water hammer arrestor using a brass drop elbow with a tee fitting beneath it to branch off to a separate arm, like a saquaro cactus? Wouldn't it be easier just to use a brass drop tee and extend the piping up to form the air chamber? When the stub out the wall is just a copper pipe, it seems common to do this with just a sweat fitted tee.

    I'm aware of the debate as to whether air chambers are useless, anyhow, but I intend to install one for the feed to a new toilet, just in case. I want to make sure I'm not overlooking something on how this should be done.
    Last edited: Nov 3, 2012
  2. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,987
    Location:
    NW Ontario, Canada
    Are you talking about a low-tech hammer stop that is just open-ended? Those will waterlog over time as the air gets absorbed. They should be mounted on the top of a Tee so as to collect any air that may be in the water stream.

    The better hammer stops have a piston with a pre-charged, closed air reservoir that are not prone to waterlogging so the air supply need not be replenished by accumulating air. They can and should be installed as you say, with an elbow so as to not accumulate air, thereby keeping the O-ring seal on the piston lubricated.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,641
    Location:
    Cave Creek, Arizona
    Three things;
    1. You already know that air chambers are only effect for a short time, until the water absorbs the air.
    2. It is almost impossible to recharge an air chamber, regardless of what anyone tell you about turning off the water and draining the pipes.
    3. A toilet is the one fixture that seldom, if ever, needs an air chamber.
  4. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,987
    Location:
    NW Ontario, Canada
    1. Assumes low tech, not pre-charged piston type.
    2. May depend on how and where they are installed.
    3. Very true.
  5. Neptune

    Neptune New Member

    Messages:
    5
    Location:
    Illinois
    Thanks for your observations.

    I agree that an arrestor of any sort is probably not necessary, but I happen to have on hand a drop ear tee but not a drop ear elbow. So, I'm thinking--why not just use that and add another 14" of pipe with a cap, just to cover old school practice?

    This, then, led me to wonder why you see the "cactus arm" configuration so often, which takes extra fittings and joints, and not nearly as elegant as using a tee.

    Maybe the answer has nothing to do with flow characteristics or the like, but simply that plumbers typically have in their trucks a supply of drop elbows but not drop tees!
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,004
    Location:
    Bothell, Washington
    It's been a long, long time since I've installed an "air chamber"

    In the plumbing code; if there are installed, there must be a way of draining them down.
    What is approved is hammer arrestors. In a tight (closed) system, those would be installed on quick closing valves.
    Ice Maker
    Dish Washer
    Clothes Washer

    All of these have solenoids.

    And yes, a hammer arrestor can fail too.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,641
    Location:
    Cave Creek, Arizona
    quote; 1. Assumes low tech, not pre-charged piston type.
    2. May depend on how and where they are installed

    1. Mechanical styles are "shock absorbers" NOT air chambers
    2. A filled air chamber is like a straw with your finger over the end of it. The liquid will NEVER drain out until air can get into it, and there is NEVER enough "pressure" to force air in, AND even if there were few systems are installed so that ALL the water can be drained.

    As far as the location, good hydraulics specifies that the inlet to the shock absorber be in line with the direction of water flow.
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