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Vapor system problems

Tambrass Member Posts: 3
I have an old Vapor system that is not heating evenly. (half of the Rads. are hot and the other half are cool). This is a two pipe system with the inlet at the top of the rad with a Arco valves, and the outlet without any traps. The boiler is installed with a standard Pressuretrol (operating at about 1.5 lbs). I intend to replace this to a lower pressure control (to operate at about 10 oz.). The system has a few devices on the return side that no one seems to know what they are, one is made by "Moline":
I feel this is an Air eliminator. There is also another device: , The system is piped as the attached drawings show. Need to stop water hammer and get the whole system to heat. Any Ideas??...


  • Jamie Hall
    Jamie Hall Member Posts: 17,103
    No wet returns?

    Step one is going to be to get the pressure down -- probably no more than 6 to 8 ounces cutout. These systems are very sensitive to pressure.

    Then I would wander around and see what the temperatures in the dry returns and mains are, to see if I could find anywhere where steam is getting into the dry return -- or not getting through in the steam mains.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Tambrass
    Tambrass Member Posts: 3
    Wet return from after "air eliminator" back to boiler. The area on my drawing labeled as " all piping inside wall is unknown" transitions to a wet return.
  • Steamhead
    Steamhead Member Posts: 14,844
    edited March 2018
    This is a "Moline Heat" system- one of many variations of Vapor/Vacuum heating. The radiator shutoffs should have orifices in them to equalize the flow of steam.

    The shutoffs on the return connections are just there in case you have to remove a radiator and run the rest of the system, as for painting the wall behind it etc.

    The huge device in the first pic is a diaphragm-operated valve that closes to hold the system in vacuum, which in the coal-fired days would allow the steam to be generated at lower temperatures.

    The second device looks like a float-and-thermostatic trap which would have been added later.

    From the diagrams, I'm thinking the air isn't getting out of the system. If the air can't get out, the steam can't get in. Try opening the hand valve near the diaphragm valve and see if the air starts coming out. If it does, you've found the problem.

    See chapter 15 of Lost Art for details. And post some more pics!

    Where are you located?
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • AMservices
    AMservices Member Posts: 597
    In your drawing with the device you call a "3 way trap"
    That is a steam ejector.
    It has a direct steam supply, the bottom connects to the end of the dry return and then goes through the big can (or the condenser) before passing through the diaphragm air eliminator/vacuum valve.
    When steam enters the ejector, it starts condensing, makes a natural vacuum and sucks air out the return.
    Air gets ejected, steam gets condensed before it hits the vacuum valve.
    Does the steam ejector ever get hot? Might be clogged with sediment. No moving parts.
    Steam should go straight for the ejector. If you can get the steam there first, everything else will heat faster.
    No traps is a good thing, but the supply valve needs to be throttled so all the steam is condensed before it gets in the dry return.
  • jumper
    jumper Member Posts: 1,713
    I always wondered about Moline ejector. Motive steam pressure is puny but required pressure increase is also modest. Very good engineering. Suspect Moline didn't go mainstream because there's so little equipment to sell.
  • Tambrass
    Tambrass Member Posts: 3
    Interesting. I'm In Pittsburgh PA. Thanks.