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Air Eliminator

Roland_18
Roland_18 Member Posts: 147
Hi All,

I know this is a noob question, but here goes. Why are air eliminators almost always shown with an expansion tank screwed into them?



Can air eliminators, such as a Spirotherm jr, be used without the expansion tank?



I'm not advocating eliminating the expansion tank. I'm just curious whether additional air removal devices can be used with a system that HAS a properly installed and operating expansion tank.



TIA, Roland..............

Comments

  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Air separators and expansion tanks.

    I am not a pro, but you certainly need not connect an expansion tank to your air separator; the separator will work no matter where the tank is.



    It seems to me that the air separator has a connection  to the expansion tank has little to do with the tank  but because the makeup water feed is usually between the tank and the separator. The rationale seems to be that the air in the incoming water might as well be removed right away, rather than circulated around the system until it finds the air separator. It would be convincing to me unless I asked this question:  "Just how much air comes into a system with the gallon a year (guessing here; maybe it is less) of makeup water?"
  • moneypitfeeder
    moneypitfeeder Member Posts: 249
    edited August 2011
    here goes

    Hopefully a pro will weigh in if I'm off base here. My air eliminator is piped to a boiler return trap. The return trap, much like a expansion tank, does not expel air on its own. So they give it a "vent" and because it also can separate the water and send it back to a return is called an air eliminator. Why are you looking to add another air eliminator?
    steam newbie
  • LarryC
    LarryC Member Posts: 331
    Air Eliminator location

    Aie eliminators are used in hot water systems to remove dissolved air trapped in the water.  Air is less soluble as the water temperature goes up.  Therefore it makes sense to install the air eliminator where the water is the hottest.  The two hottest locations are on the top of the boiler and immediately coming out of the boiler.



    Air bubbles are easier to remove when the water velocity is slower.  That is why you will find air eliminators on the top of the tanks used for boiler and piping hydraulic separators.



    Air also comes out of solution at lower pressure.  If you are pumping away from the point of no pressure change, then the expansion tank should be the lowest pressure location in the closed system.  Combine two functions at one location.  Make the pipe wide to slow down the water, add a connection for the expansion tank, and add a connection for the air eliminator.



    Since air bubbles are less dense than water, you will sometimes also find air separators in place of vents at the top of risers for distant radiators.



    Recap: hot, slow, and low pressure water is the best places for air to come out of solution.  If you need to remove the air, those are the places to do it.



    PS  I am not a heating professional but I like the subject.
  • Charles Johnson
    Charles Johnson Member Posts: 24
    Good post Larry

    Great post, esp coming from a non pro!



    Just one thing to add, if the feed water is piped in anywhere but the point of no pressure change (expansion tank), the pump turning on can change the static fill pressure.



    So yes, tank, air eliminator, and feed should be piped in at the same place in the piping, upstream of the pump.
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