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McAlear system

jvl1 Member Posts: 11
I have run across a home in Hamilton Ohio that has a W-M EGH-125PIN-S steam boiler that was having trouble getting steam to farthest radiator before boiler shut down on limit. Owner actually had original blueprints which showed a McAlear #758 air eliminator and return trap piped from supply line to return and each of the six return lines had McAlear vents, identified in the print as McAlear #14 (quantity 3) and McAlear #15 (quantity 3). Over the years these vents have been replaced by Hoffman #75's and the 758 was removed and tappings were capped. Everything else on system is operating properly (low steam pressure, 1/2#cutin/1-1/2#cutout, all other radiators heating properly, combustion checked, piping per installation manual etc.). I know the McAlear systems were many times vapor systems. All radiation has had new, standard radiator valves and Hoffman 17C traps installed so it is no longer operating in vapor. The only thing I can think is we are not venting the air fast enough.. Can't find anything on the McAlear vents but believe with the 758 installed as, basically, a cross over trap, that massive amounts of air were vented on start-up. Thinking they should go back with a higher capacity vents to replace the 75's, such as the Gorton #2 and maybe a Gorton "C" on the trouble radiator. Thoughts?


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    A piping diagram would help us understand the layout better.
    Increasing the venting would certainly help, and the Big Mouth is the king of capacity, As it has no float in it, I would mount it as high above the waterline as possible, and keep the pressure lower than standard, with a vaporstat and low pressure gauge graduated in ounces.
    The standard pressuretrol is pretty useless at low pressures, and when set lower, can suffer from linkage disconnect, and allow runaway pressure.—NBC
  • Jamie Hall
    Jamie Hall Member Posts: 23,419
    Is there any good reason why you can't install a crossover trap where the 758 had been, and then make sure you have good venting on the dry return? That might make a big difference. The crossover trap doesn't have to be fancy -- chances ate a 17C would be big enough. The dry return vents do have to be good and big, though!

    And I'd surely consider a vapourstat...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 16,886
    Sounds to me like this is pretty standard Vapor, using McAlear hardware. Use the Big Mouth as a crossover trap, the way we did here:


    then vent the dry returns with Gorton #2 vents, which have floats to keep water from leaving the system.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service