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compression/expansion tanks

rohanrohan Posts: 1Member
I just got into an agency that never had a maintenance program. I have come across a few commercial boilers of varying BTU's that have compression tanks with gauge glasses. Each one is completely filled with water. I'm debating whether I should install airtrol tank fittings and attempt to maintain proper water/air levels or change the tank over to a diaphragm expansion tank. Any insight would be appreciated.
overkill is under rated


  • SteamheadSteamhead Posts: 12,039Member
    Diaphragms are moving parts

    and will eventually fail. Airtrol fittings are not. I'd go with the Airtrols.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
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  • Mark EathertonMark Eatherton Posts: 5,833Member
    Never thought I'd say this, but….

    The old tanks you have, IF properly set up, are going to work best for you. Look around the system. If you find any automatic air vents, close them off or better yet, eliminate them.

    And yes to the use of an Airtrol fitting.

    With this style of tank, you must NOT have any automatic air vents ANYWHERE in the system. It will expel the cushion and the tanks will water log.

    If you go with the diaphragm or bladder, you MUST have air separators/auto air vents…

    Regardless of which direction you go, be sure an install a drain valve between the tank isolation valve the the tank for proper service.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • M LaneM Lane Posts: 123Member

    Keep in mind that if you get into ASME ratings (over 200 MBH) , your expansion tanks would be very expensive.
  • RJRJ Posts: 484Member
    exp tank

    I agree with Mark,   The benefit of the compression tank is that any air  that may get into system from after any repairs will end up in tank if installed correctly.  diaphram or bladder tanks do not afford this. Bell and Gosset makes a number  of valves that shoud be installed on the compression tank,  airtrol fitting, tank fitting and drain valve.  I would normally have to drain the tank at least once during the heating season, and check the guage glass gaskets for leaks.
  • icesailoricesailor Posts: 7,265Member
    Compression tank leaks:

    All good advice. The two biggest places I found leaks on compression tanks are on the upper part of the gauge glass and if they use any kind or vacuum breaker fitting to drain the tank. A generous amount of Teflon Tape and Teflon Paste on the threads and seat of the plug does wonders. Leak detector on the upper part of the gauge glass is helpful. But the leak is so slow, it's hard to tell. Take out the gauge glass and replace the rubber rings. Lube up with synthetic grease.

    If there's white dusty scuzz on the glass at the top or bottom, change the gaskets. Change the whole glass for that matter. Then, you need a cutter. If you don't have one, buy one. Don't buy the cheapest one. The better one isn't much more and cuts properly every time.

    If you want to make life easy for yourself, add a boiler drain to the tank in an appropriate place (if you have a gauge glass) and charge the tank with compressed air. It may be a "Exercise" to do it, but you can pre-charge the tank to 1/3 full of water with the proper pressure without doing a lot of unnecessary work.

    It worked for me.
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