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The lag boiler overfilling with the lead boiler on & visa versa

Tom_65 Member Posts: 2
There is 2 Kewanee 36 HP boilers each is fed with their own pump from the receiver tank. The feed line goes up about 10' and then over to their respective boiler. The system is set up to rotate boilers every 12 hours. While there I witnessed the lag boiler with a full sigh glass and the lead boiler at normal level switch over. As soon as the lag boiler started to build pressure the sight glass went to a normal level and the lead (now the Lag) boilers sight glass fill completely up. There are 2 check valves in each of the condensate lines from the pump to the boiler. When I went from lead to lag with the ball valve on the condensate line closed to the new lag boiler the problem went away. I am considering installing motorized valves in the condensate line to eliminate this problem unless there is another solution.


  • Tom_65
    Tom_65 Member Posts: 2

    I forgot to add that both boilers have vacuum breakers installed on them.
  • Jerry Boulanger_2
    Jerry Boulanger_2 Member Posts: 111
    The lead boiler

    is steaming into the lag boiler, where the steam condenses and fills up the lag boiler.

    Simplest solution is to install traps off the drip line on each boiler a couple inches above the normal water line. This will prevent the water level in either boiler from ever getting too high.

    It's all in Dan's 'Lost Art'.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Jerry is right

    a "skimming trap" is often done. Sometimes in addition I have used an equalizer between the boilers below the water line so if one skimming trap hangs up the other will keep level. I learned that from Ray Stevens, Rest His Soul. An Engineer's Engineer. And a Dead Man.
  • Here's a method

    that is in the Burnham Heating helper with F&T traps and Motorized Globe valves. Hope this helps.

    Glenn Stanton

    Manager of Training

    Burnham Hydronics

    U.S. Boiler Co., Inc.
  • Overfill boilers


    I used the exact pipe arrangement that Glenn posted for the F&T traps in the drip headers, on a set of Burnhams I installed in the local Penn State Uni. Campus about 20 years ago, and it has worked flawlessly ever since.

    Glenn’s diagram says it will maintain the water level in the unfired boiler and it does. Actually, when the water level goes above the trap it will simply unload to the condensate tank and maintain the water at the elevation of the traps in both boilers, regardless if the boiler(s) are running or off.

    Good Luck Tom,

    And Merry Christmas to all

    Ed Carey
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