Reply To: Water expansion tank

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Avatar photoSylvanLMP


    Originally posted by Harold Kestenholz:
    Absolutely right about that, Sylvan. I am still puzzled about this post. I was not aware of non-diaphragm expansion tanks being used on such installations. I have never used or sold one for this purpose.


    Harold HOW do you know this Person doesnt have a “bladder type” and thinks its a non bladder one he has?

    REMEMBER a lot of folks call a boiler a furnace and a boiler a hot water tank so WE are at a total disadvantage not actually seeing what folks are talking about

    Certainly ASME high-pressure vessels are used commercially, but I am still curious about this use on a residential system. Piped so the expansion tank is above the heater, air bubbles separating from the water as it is heated would collect any air and hydrogen produced in the process, so purging would not be necessary until hydrogen collects. The tank would have more than enough air; so the tank in this post must be too small. Then I would not encourage a smoker to purge the tank. If this is an old boiler expansion tank in use on a water heater, I expect to hear the report from a long distance at any time.

    Answer Sylvan

    Harold again thinking like US Heating guys we know any steam boiler GREATER then 15 pounds working pressure is considered HIGH PRESSURE

    We also know any hot water boiler operating at 160 POUNDS and a temperature of 250 degrees is STILL considered low pressure according to ASME section IV and NBBI

    Now lets take a pressure vessel like a hot water tank RATED to 300 pounds and a Normal working pressure of 125 and a pressure relief of 150 pounds.

    If for some reason this tank does become slightly air bound ZOOM PRESSURE BUILDS very FAST even if you did have a an “expansion tank” to take up for the pressure temperature relationship,

    I doubt very seriously it could handle all this excessive presure build up.

    Remember even a hydronic system does NOT expand that much ( like a vapor system as water is hard to compress).

    With the new devices to prevent back syphonage the need for any type of expansion tank is now needed more then ever before.

    X TROL makes one for just hot water tanks for expansion during non peak hours when the city water preesure can increase by over 30 pounds PLUS compounded by heat here goes your pressure temperature relationship.

    Your thinking like a heating guy looking for the stradification of air buddles in a closed system.

    A domestic hot water system lets in FRESH water constantly hence MORE oxygen and more buddles so this is not really the problem in this system we are concerned about as every time a faucet is opened good bye bubbles ESPECIALLY on the upper floors.

    On LARGE domestic hot water systems I have been known to install a automatic air vent like a Hoffman 78 rated for 150 PSI @ 250 degrees BUT I lower the T&P to a 125# model even though I know the Hoffman can with stand pressures up to 450 PSIG.

    This is only for my very large commerical accounts would I need this kind of protection for possible air pockets as I hate having my bronze circulators cavitating as they can build up lots of heat and go BOOM.


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