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To owners of Vapor systems..

tmw Member Posts: 56
My Arco Model K is designed to run on 3oz. I don't know if this means that it's acceptable to climb a few ounces and cut out, for example, at 6oz after a 20 or 30 minute run while warm (or perhaps cut out at 6oz after a 50-60 minute run if system is cold),  or stay at 3 oz until t-stat is satisfied.

I've read a bunch of posts from folks who run at very low pressures, but can't seem to find any info on whether these systems cycle off-on, or stay at low pressure until t-stat is satisfied.

I'd be grateful if a few of you would share your experiences. Are these systems supposed to find an equilibrium where steam generated=condensation formed and just stay at a certain pressure? If so, every time you open or throttle down a radiator do you change the equilibrium?


  • haaljo
    haaljo Member Posts: 112
    Article on low pressure

    This article is about pressure:


    I have a plain old one pipe system. This heating season I cannot raise pressure according to my 3 pound gauge. The gauge flutters above zero but doesn't even reach one ounce. Don't have to add water so no leaks. Filled the boiler to the top and no leaks.

     I made a manometer. The water level drops two inches when the radiators start to get hot. Then the water level returns to the normal level when the radiators are competely hot. So, maybe that means the pressure is about one ounce?

    In any case, all the radiators get hot and the boss is not complaining about comfort or noise. Perhaps, the burner needs to be cleaned and adjusted (underfired). Bottomline is if your system is working well at 3 ounces, why would you want to start cycing on pressure?
  • haaljo
    haaljo Member Posts: 112
    Low pressure concern

    Good question,

    Intersting that you didn't get responses so I'm responding again to update the thread . You have to ask your question not only to owners of vapor systems but also the Pro's. My guess is the Pro's would say 3 ounces is fine and to leave alone.

  • Joe V_2
    Joe V_2 Member Posts: 234
    Mine runs at 3 oz...

    to 5 oz before satisfy the t-stat.  I have a 1.5 to 15 psi pressuretrol set to cut off at 1.5 psi.  The only time the pressuretrol has ever turned off the boiler was when I had  a -10 degree night timeset back.  But usually, the burner runs upto 25 minutes at 3-5 oz until the t'stat is satisfied.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314
    Joe thats how it should run

    the pressure trol is more of a safety shut off if the boiler is properly sized. That is if you are happy with how the heat is distributed and the system is quiet aside from normal combustion related noises.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Joe V_2
    Joe V_2 Member Posts: 234
    edited March 2010
    I know

    And I'm very happy with it. Runs flawlessly and the cat loves laying on the radiators.

    I still think I'll put a vaporstat on it next heating season because during that one event I described, so much condensate returned at one time, water came out of the return's vent. 
  • Jamie Hall
    Jamie Hall Member Posts: 22,947
    for what it's worth...

    Hoffman equipped vapour system; 7,000 square foot 1810 - 1890 museum/house, very complete records.

    The heart of the Hoffman system was the differential loop and the draught controller.  The draught controller was a beautifully sensitive device which controlled the draught over the fire to hold about 3 ounces pressure, assuming that someone had fed enough coal to it.  The differential loop activates at 8 ounces, more or less (and still does!).  The loop was a protective gadget, and functioned if the draught regulator hung up, causing the pressure to rise.  Without it, it was possible to back the water out of the boiler; what it does is put live steam into the returns, and pop the water back in.  Clever.  No moving parts.  On the original coal boiler, I don't suppose it ever got tripped (that was before my time!). 

    Now the system runs at about 2 ounces until all the traps close, which normally never happens (only happens after a big setback).  The vapourstat is set to cut out at 7.5 ounces and cut back in at 1 ounce.  If there has been a big setback (or the oil company has run me out of oil...) the system will cycle on the vapourstat after about 50 minutes or so of running, and keep doing that until the thermostat is happy.  I run a three degree setback, and the system doesn't have to run that long normally.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • tmw
    tmw Member Posts: 56
    Terrific responses..

    It looks like my system is now in a fairly decent state of tune..stays at 3oz for 20-25 mins. in the morning after a -3 deg. setback. Then cycles off on t-stat. Will stay at 3oz for 50 minutes if need be after a larger setback. 

    Let's hear more from vapor system owners!
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