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expansion tank connection side down question

ron Member Posts: 407

found this statement in a previous post however long ago

Consensus seems to be connection side up
IBR Guide: "Always mount the tank with its system tapping UP, never on its side or upside down. This ensures the diaphragm will always be wet, avoiding cracking due to drying out of the elastomatic."

mounting with threaded connection up, such as with using the old taco air scoop (which is the only way you can do it with a taco air scoop) then when the bladder in the tank fails the tank will fill with water and offer no compressible air buffer to manage water thermal expansion.

but if you mount the tank upside down, so to speak, with the tank connection on the bottom, then technically you don't even need a bladder in the expansion tank right? Because if the bladder does fail the air is going to be pushed upwards into the tank is it not and there's no where else the air can go? So isn't the argument of how the diaphragm not being wet and cracking and drying out kind of a mute point if you mount the tank upside down?

With the expansion tank mounted vertically and connection side down, regardless if the inner bladder or diaphragm is good or not won't the tank function indefinitely... until it rusts out and springs an leak externally?
Alan (California Radiant) Forbes


  • If only they made see-through tanks where you could see what the diaphragm was doing and where the water level is in different mounting positions.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • Jamie Hall
    Jamie Hall Member Posts: 21,095
    Far as I can make out it should make no difference, and seems to make no difference. Keep in mind that one side of the diaphragm is always wet and the other side -- you hope -- is always dry, no mater which way up the thing is. Old style compression tanks didn't have a diaphragm, so they had to be mounted with the system connection on the bottom -- but because they didn't have a diaphragm, they also had to have some ingenious way to keep the right amount of water in them.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 10,564
    I feel that if the water and air can come in contact then some air will go into the water.
    As that water slowly is moved in and out of the tank (as heated and expanding) and passed thru any device designed to remove air, eventually that head of air would be absorbed into the water and be expelled from the system.

    For the same reason an old school compression tank system should have no air removal devices in the system. The design is such that any air would end up in the compression tank.

    And the compression tank had a lot more "air head" than a small expansion tank has.

    Although adding air to a bad bladder tank that is mounted fitting down would be a short term fix.
  • hot_rod
    hot_rod Member Posts: 19,266
    Zilmet shows all position mounting. Amtrol mentions horizontal with proper support. I don't think life expectancy changes with position?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EBEBRATT-Ed Member Posts: 13,427
    Seems to me that hanging down is more correct. Horizontal could trap air on the water side
  • MikeL_2
    MikeL_2 Member Posts: 422
          Dan posted on this subject in July 2006 with input from Amtrol. They recommended threaded connection up at the time.