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boiler expansion tank Operating/Air Flow Valve

I have an old valve on my gas hot water boiler expansion tank. Is it supposed to be 'sealed' at the bottom and water flowing down but stopped by the end cap OR is it ok there's no end cap and the valve turned off? I thought it was supposed to be off but the expansion tank is not hot at the bottom at all. The pipe leading up to the tank isn't hot all the way up to the expansion tank either. Also I noticed the valve bottom seems to have had sealer on it for a steel end cap. So I was thinking maybe it's supposed to have a cap and the valve on so water/air can flow in tank. Or maybe this a type of valve closed or open it lets water/air flow thru it from the top and side but only closes/opens the bottom part.

I'm having minor psi problems and I think there's air in the system. After 5 different heater men I am trying to figure this out for myself.

So my main question is does anyone know what kind of valve this is? And is it supposed to be 'on' or 'off'


  • newagedawn
    newagedawn Member Posts: 586
    edited December 2017
    need a bigger pic to see
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • Michael60622
    Michael60622 Member Posts: 9
    Here is side view.

    And it does say "Operating and "Air Charge". I think it's on Air Charge now.

  • Jamie Hall
    Jamie Hall Member Posts: 22,147
    Still can't really see it -- but sort of guessing from what I can see... it looks as though the purpose of the valve is to shift between connecting the tank to the system, so it can operate as an expansion tank in the usual way, or to open the tank to drain -- perhaps even in such a way that it doesn't drain the system at the same time, which would be rather nice of it.

    The idea of the expansion tank is that it should be about half full of air when the system is at operating pressure. Then it provides a space for the water to expand as it heats, without changing the pressure all that much.

    If it should get waterlogged -- lose all of the air -- you would need to shift that valve to drain, drain all the water out, and then shift it back to system and bring the system pressure up with adding a little water.

    I'm not going to go out on a limb and tell you which way to turn it to connect to system or drain... easy enough to find out!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Michael60622
    Michael60622 Member Posts: 9
    That sounds right to me Jamie. I think this valve is supposed to let you turn off the water going to tank so you can do whatever to the tank. Maybe this valve has to be turned all the way over one way or all the way the other? I can't find any info about it.

    The thing that makes me think something is up is the pipes leading up to the black expansion tank aren't hot all the way up. And the expansion tank is ice cold on the bottom. Also that bottom pipe looks like it had pipe sealer on it once upon a time for a cap.

    I tried to open the valve and get a pex pipe up thru the valve to make sure the expansion tank has air in the top. And the water got real hot fast. It got so hot so fast I had to turn the valve back off.

  • Jamie Hall
    Jamie Hall Member Posts: 22,147
    Water doesn't flow into or out of the expansion tank in any great quantity -- a little bit in as the system warms up. A little bit out as it cools. I wouldn't expect the tank -- or the pipe leading to it -- to be hot or even really warm, particularly in a cool basement.

    Is there a sight glass on the side or end of the tank? There often is. If so, if the water level is about half way up the glass -- more or less -- you've got enough air and water in there.

    And if the pressure on your system is holding reasonably steady, the tank must be open to the system and doing it's job.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 14,534
    The valve says "operating" and "air charging" so it should be kept in the operating position. In the operating position the boiler is connected to the expansion tank and the third connection to the valve (the open connection) is closed. When you turn it to "air charge" you should be isolated from the boiler and the valve opens to the expansion tank so you can drain the tank of water and let it refill with air and the open connection is open

    At least that's the way it looks to me
  • Michael60622
    Michael60622 Member Posts: 9
    hrmm well it seems like that valve is bisexual. I tried turning it to operational and keep turning and turning it and the water flow slowed down big time. But it didn't totally stop. I think that's why there was a cap on the bottom they didn't want to replace the slightly faulty valve.
    Now the pipes leading up to the expansion tank and the valve are hot. The heater was running at 29ish now is at 20ish psi.

    Your a genius.