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Mouat Vapor Heat Steam Traps

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Need some help on an older system. If we choke back on the header valves the radiators get warm, and if we open the header valves the result is worse.

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  • Steamhead
    Steamhead Member Posts: 16,902
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    Tom, the first thing I'd check

    is whether the dry return is somehow being pressurized. The usual cause is bad traps, but if the boiler has been replaced it might be a piping problem too. Look for connections between the steam main and dry return that used to be under water with the old boiler, but are now exposed with the new boiler's lower water line.

    Does this Mouat have thermostatic traps or water-seal units?

    Also, what pressure are you running, and is the boiler grossly oversized?

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  • steve_6
    steve_6 Member Posts: 243
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    we work on mouats

    all the time .not quite understanding your question though. Mouat had both thermastatic and water seal traps
  • gerry gill
    gerry gill Member Posts: 3,078
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    hi ya steve,

    sounds like when he throttles the king valves everything is fine...least thats my take..gotta be blowing thru a radiator and pressureizing the return..by the way, with mouats you need to downfire the gas...mouats boiler simmered.
    gwgillplumbingandheating.com
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • steve_6
    steve_6 Member Posts: 243
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    just a few more things

    First off leave those king valves open. T.G. Mouat designed his system too run at 3 ozs. or less at the boiler. that means like Gerry said you have to downfire the boiler to get it to run at that pressure which is how they accomplished this on a coal boiler with a damper regulator. Next is that mouat designed his settable radiator valves to work with his water seal radiator traps. The key in this system is to set all the radiator valves so every radiator heats at the same rate and that those valves are throttled and set to allow just the right amount steam into the radiator that it could condense therefore preventing steam from blowing through that trap and into the dry return. If the radiator valves can"t be throttled and set , they should be replaced with an oraficed valve only. Mouat still used these settable valves when he changed to Mouat / Ideal style themostatic traps.
  • AndrewS
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    Fitting type used on Water type traps?

    I found that one of my old Mouat water traps was leaking from the large nut which attaches the pipe from the radiator to the trap.  I soaked the nut with WD40 for a day and then spun it off.  The pipe appeared to have a small ring on it .. at 1st I thought it might be a backing ring for a packing of some type.  But it seems fixed to the pipe.  I viewed Gill's pdf which shows a cut away of the trap and it seems to have a chamfer for a packing. 



    But no packing or remains of one with the current valve fitting.  So is it more of wedge type fitting that just needs a good cleaning and tightening? 



    thx



    - Andrew
  • AndrewS
    Options
    Fitting type used on Water type traps?

    I found that one of my old Mouat water traps was leaking from the large nut which attaches the pipe from the radiator to the trap.  I soaked the nut with WD40 for a day and then spun it off.  The pipe appeared to have a small ring on it .. at 1st I thought it might be a backing ring for a packing of some type.  But it seems fixed to the pipe.  I viewed Gill's pdf which shows a cut away of the trap and it seems to have a chamfer for a packing. 



    But no packing or remains of one with the current valve fitting.  So is it more of wedge type fitting that just needs a good cleaning and tightening? 



    thx



    - Andrew
  • Jamie Hall
    Jamie Hall Member Posts: 23,446
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    The very first thing

    I'd look at is your pressure.  If you are not using a vapourstat, the probability is excellent that the pressure is too high.  Like... way too high.  As has been said, a Mouat runs at 3 ounces or less -- which is hard to achieve, even with a vapourstat, never mind a pressuretrol.  If there is even one water seal left somewhere in the system, the first time the pressure goes too high it will blow, and the dry returns will get steam in them, and you're out of luck.



    Check that first.  Then check Steamhead's comments on a return which was supposed to be wet and isn't any more -- a dismayingly common situation.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • AndrewS
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    Yup, it has a vaporstat

    Yes, the system is set up properly with a vaporstat and is set for

    several ounces.  As I'm in Cleveland, I had Gill stop by a few years ago

    and check the system over.  At that time we had the wrong thermostat

    type which prevented the boiler from firing at a low rate.  He changed that out and the system works quite well now.



    I

    cleaned up the fitting, removed the corrosion which had accumulated,

    and tightened the nut on the water trap.  This seems to have solved the

    leak issue.   



    I re-opened the Mouat valve and the top of the

    radiator is hot while the bottom is somewhat cooler.  You can feel a

    little heat in water trap. 
This discussion has been closed.