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Thread: Hello! I'm new, and what's with the expansion tanks?

  1. #1
    Plumbing Instructor Plumb or Die's Avatar
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    Default Hello! I'm new, and what's with the expansion tanks?

    Hi, I'm Shawn and new to the forum. I've been a journeyman plumber since 1995 in Canada, and am still learning new things on a daily basis like everyone else. I just started teaching at a technical college, which is a beautiful thing. I've installed many boiler systems and of course they always get expansion tanks, but swear to God, I've never heard of using them in a domestic water system utilizing a hot water tank, electric or gas. They're not required in either the Canadian National or BC Plumbing codes. So what's up?
    I like plumbing. Plumbing's my favorite.

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    Moderator & Master Plumber hj's Avatar
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    Default tank

    For the same reason you put them in a heating system. In a closed circuit, heating water creates a pressure rise, and it can be rather dramatic in its speed and degree. A potable water system can normally relieve the pressure to letting it escape into the city's main. BUT if the house has a pressure reducing valve, or a check valve, in the supply line it creates that closed system, and the expansion tank, if configured properly, will absorb the majority of the pressure build up.

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    In the Trades Gary Swart's Avatar
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    Default

    Just to tag on to HJ's message, if you have a closed system and do not install an expansion tank, the TP valve will trip every time the water heats.

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    Plumbing Instructor Plumb or Die's Avatar
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    Default Tanks a lot

    Thanks guys. I guess closed systems aren't too common around these parts. I've installed swing checks on houses with black municipal tube water services but haven't seen a true "closed" hot wter system before. Interesting stuff.
    I like plumbing. Plumbing's my favorite.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Default

    If you have a swing check on the incoming water, then that's as closed as you can get.

    Since the water can't back up into the main, it only has one thing it can do. and that's expand.

    When it does expand, the pressure will rise.
    When it rises enough, that's when the Pressure relief on the water heater can trip.

    The other thing to worry about though is the tube running through the gas water heaters, the added pressure bends the tube inward, and eventually can break the weld joints.
    The other thing you will need is hammer arrestors that don't water log.
    In the states, you would be installing them on the washer (h&c) dishwasher (h) and icemaker (c)

  6. #6
    Master Plumber master plumber mark's Avatar
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    Talking you ar a lucky guy...plumb or die

    I wish I could be teaching some where at a
    technical college myself......

    stick with the teaching and do the plumbing on the side
    in your spare time....


    It would be my personal preference......

    because the dumb ass apprentices I have had to
    try to train lately are starting to wear on my brain
    like a belt sander.....

    slowly melting my mind....

    teaching would probably bring me back to the living...


    but then again---I wonder who I might get to teach??
    Last edited by master plumber mark; 01-13-2007 at 05:59 PM.

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