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expansion tank piping

brad johns
brad johns Member Posts: 5
I went to Dan's seminar here in Milwaukee a while ago and he touched on how an overhead expansion tank without an Airtrol fitting can pull air back into the system, but I cannot for the life of me remember the reason, if someone knows it off the top of their head and can refresh my memory that would be great. Thanks.


  • Empire_2
    Empire_2 Member Posts: 2,343
    Hey Brad.........

    Since air can be absorbed in water, some means of restricting the flow (gravity circulation) from the tank into the system is needed. This device will also allow the passage of air in the system to go to the tank. In a nut shell the device stops the migration of cooler water which is entrained with air from re entering the boiler.

    Did that help?

    Mike T.
  • Big Ed_3
    Big Ed_3 Member Posts: 170
    Air Migration

    First remember cold water absorbs air, hot water releases air and hot water rises while cold water falls

    In the riser that connects to the expansion tank . Usual a 1/2" copper pipe . A small current will form with in that pipe , Caused by rising hot boiler water and cooler expansion tank water . It small enough to pass with in that single 1/2 " pipe .

    The air depleted warm water rises up in to the tank , then cools off , The cool water will absorb some air from the tank . Now when that cool tank water is caught up in the riser current back to the boiler , it will be heated up and release the air .

    The air end up in that first "Trouble" radiator where some one installed a auto vent . Now when the airs all gone,,,,,,,,,,,,,,,,you know the rest.
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