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hot water heating system expansion tank (no bladder)

JimGlose Member Posts: 3
I replaced the body gasket between the Bell & Gossett bearing assembly and the pump body last night . . . afterward, I put everything back together and started to pressurize the system. With the boiler off and cool, I drained the expansion tank a little and refilled it to where the Airtrol fitting began to spit. I turned the little nut on the fitting to stop the flow of water from the tank . . . but I think the tank kept filling with water. I did the drain/fill/spit thing a few more times with the same results.

It's been five years since I last replaced that gasket and I don't remember what to do to re-pressurize the system.

Any help is appreciated.



  • MikeSpeed6030
    MikeSpeed6030 Member Posts: 69
    The tank needed to be completely drained and vented to atmosphere - so that it is initially 100% full of air. Then re-pressurize the system, and the air will be compressed.
  • Gilmorrie
    Gilmorrie Member Posts: 146
    By just draining a dribble from the tank, you didn't get the job done. Best to vent the tank while draining. (Your Airtrol tank fitting can help break the suction.) When draining, wait for the "glug-glug-glug" sound as air is sucked into the tank. You need the tank completely drained and full of air.

  • Steamhead
    Steamhead Member Posts: 14,832
    What Mike and Gilmorrie said. I'll add that the pipe from the system to the tank should come from the air separator. This way, system air gets routed into the tank and it won't waterlog, assuming there are no automatic air vents on the system.

    I prefer this setup to the newer diaphragm tanks, since it has zero moving parts.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Mark Eatherton
  • Jason_13
    Jason_13 Member Posts: 299
    I am with steamhead on this one. The old style tanks are considered maintenance free tanks. The bladder type tanks you need to drop pressure and recharge as needed.
    Remember no auto-air vents on non-bladder type tanks.