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Waterlogged Compression tanks

Just visited a job site where two large 80 gallon compression tanks are getting filed with water . It seems every 3 weeks or so after tanks are drained they refill and must be drained. The installer added a water meter to the fill and less than a gallon of water has been added in the 3 weeks since they were last drained, but tanks are nearly full. The system has NO air separator at all and the line to the expansion tanks is directly off supply header.  The tanks show no evidence of any water leaking at all.

I am thinking that the tanks either have pinhole leaks in the tanks or perhaps the gauge glass washers are leaking air. Any other clues... AS I indicated there is no visible water leaks and no evidence on the meter of water added.  The contractor wants to replace the tanks with a single large bladder type expansion tank. I also encouraged them to add a Micro-bubble type air separator.



  • SWEI
    SWEI Member Posts: 7,356
    More info

    are these bladder tanks, or air-over-water?  If less than gallon of water has been added, what happened to the system pressure? 
  • Prisco Panza_2
    Prisco Panza_2 Member Posts: 12

    They are air or water tanks and the boiler pressure rose to 45 psi so the contractor changed them to 50 psi valves
  • SWEI
    SWEI Member Posts: 7,356
    When did this start happening?

    is there a time in recent memory when this problem did not exist?

    How old is the system?  How many stories is the building?
  • Prisco Panza_2
    Prisco Panza_2 Member Posts: 12

    Three story building and this began about three months ago ?
  • RJ_4
    RJ_4 Member Posts: 484
    exp tanks

    Go to the main wall jan. 9  2014          compession/exp tanks
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    edited March 2014

    Someplace, some where in this system, usually at the top of a riser(s) there is an innocent looking automatic air vent. THAT is your source of trouble. It is allowing the cushion from the expansion tank to be expelled.

    Find them, and eliminate/disable them, or as your friend said, set diaphragmatic tanks and an air eliminator and move on.

    These systems are a lot simpler than one would think. If it is a bladder less tank, then NO AIR ELIMINATORS CAN BE ANY WHERE in the system.

    If it is a bladder type of tank then you MUST have air elimination. Trying to cross pollenate these two very different systems never results in a good experience.

    I'd almost bet that if you ask the maintenance department, they will tell you where the previous contractor installed all of the auto vents trying to get rid of an "air" problem… And he did get rid of the air problem, but now you have a water logging problem, and they are related. Putting a 50 pound relief valve on it is the LAST thing I'd recommend be done. I hope the boiler vessel is rated for that pressure, otherwise he just bought a boat load of liability.

    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.
  • jumper
    jumper Member Posts: 1,619

    Somehow hydronic systems breath. When they lose air PRV feeds additional water. Shut off makeup water and see how soon pressure drops. I prefer gas over water expansion tanks. Here's an idea to consider. First make certain that automatic air vent operates properly, that is it doesn't pass liquid. Then connect outlet from the vent to expansion tank. You can use small flexible tubing.
  • icesailor
    icesailor Member Posts: 7,265
    Compression tanks:

    Did the maintenance personnel add a 50# relief valve a and raise the pressure in the system to 50#? That's way to high for a 3 story building. The higher pressures in the system will accelerate the absorption in the expansion tank.

    A great source of air loss in expansion tanks is if you have one of those combination drain and vacuum fittings that let you let air into the tank while draining it. They usually have some sort of plug with a tapered end. After years of use, the ground joint faces get dinged up. I always wrapped them with Teflon Tape.

    If you think the gauge glass rubber sleeves are leaking, hit it with high quality gas leak detector. If it bubbles, its leaking.

    More important, if you can isolate the system from the boiler, make sure that the pressure reducing valve is working properly. Like if it is set for 12#, that it opens around 12# and shuts off at around 12#. If it doesn't open until the system pressure drops to 5#, like ME mentions, any auto vent above the boiler will suck air and create problems. If its an old CI 30 YO fill valve, replace it. I've seen a lot of quirky fill valves drive someone nuts.

    And if the "maintenance" folks are so smart, rig them up with a place to connect a air hose with a air compressor so they can add air to the expansion tank and "pre-charge" the expansion tank. A big mistake for some is to drain the tank with a tank drain. Then, start filling the expansion tank while a vacuum exists. Instead of having the tank as 1/3 air (on the top), you can fill it with 2/3's air. Mark the gauge glass between 1/3 and 2/3. It will give them something else to do besides drink coffee and look at the women.

    You may have to explain the finer points to this. Like opening a drain to let the excess water out of the system.
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