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vapor system

What is the real difference between a steam system and a vapor system---and how would I identify a vapor system ? What should I be looking for ?


  • Jamie Hall
    Jamie Hall Member Posts: 22,162
    Well now...

    The major difference is, of course, design pressure.  Vapour systems were designed to run on very low pressure differentials -- on the order of a few ounces -- while non-vapour systems typically were designed to run on slightly higher differentials; say a pound or so.

    One whole class of steam systems is out right away -- I, at least, have never heard of a one-pipe steam system being thought of as a vapour system!

    Then there are systems which are clearly intended as vapour systems.  The common characteristic there, if I had to pick one out, would be a lack of traps on the radiators, their function being replaced by any one of a whole raft of miscellaneous arrangements to limit the amount of steam in the radiator to about 80% to 90% of what the radiator can condense.  Usually these take the form of some kind of orifice or flow restriction, either in the inlet (maybe an orifice, may be a restricted valve opening) or in the outlet -- or both.  These systems all have in common that they won't work, or will only work very poorly indeed, if the pressure is over a few ounces.

    There are what might be thought of as hybrid systems, such as the Hoffman Equipped or several others which do have traps on the radiators, but are still intended to operate at very low pressures (again, ounces).  Usually these can be identified by one or another of the peculiar (and I do mean peculiar -- sometimes very peculiar!) appliances which are related to the system -- differential loops, mercury controlled vents, specialized valves, etc. etc.  These are vapour systems still.

    Most, if not all, vapour systems had dry returns, and the vent(s) were located near the boiler.  Most had mechanical vents of one kind or another -- often with a feature to hold a vacuum as steaming rate dropped -- but some just had a condenser for stray steam, if any, and some had nothing but a pipe into the chimney!

    Where things get interesting is when systems have been modified over the years, usually with good intentions and little understanding.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 16,468

    Gorton marketed a one-pipe vapor system in the 1920s, as well as a two-pipe one. The #2 vent we all know and love came from that design. We've seen some of their one-pipe systems.

    Broomell may have trademarked the name "Vapor" since their literature used the term extensively, but other manufacturers who also designed ultra-low-pressure systems had their own names. Hoffman Controlled Heat, Webster Modulation and Type R, Richardson 3-in-1, Thermal, Dunham Home Heating System and Return System were some examples.

    Some of Broomell's contemporaries such as Vapor Engineering (VECO) and Vapor Regulator Co did use that term though. These systems were similar enough that I wonder if they were somehow related.

    Regardless, the term Vapor came to be used for any steam system that ran at ounce pressures and did not use air vents on the radiators.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • crash2009
    crash2009 Member Posts: 1,484

    that Hoffman differential loop, that you have hanging on the chimney would suggest that yours is/was a vapor system.  Are you thinking about restoring it to it's former glory?
  • Jamie Hall
    Jamie Hall Member Posts: 22,162

    learn something every day... well, why not one pipe vapour, now that I think about it?  Just keep the pressure low and there you are!

    Thanks, steamhead!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • turbobike
    turbobike Posts: 28
    vapor or not?

    differential loop is currently part of the working system.  I don't know how much restoration my system needs..  Should I consider replacing the pressuretrol with a vaporstat?

    I have replaced all of the steam traps.  Main vent replacement is next.  I want to go with a Gorton #2, but vertical space is limited.   Can I run a 90 degree out of the top of the differential loop (where present Dole valve is) into a 12 to 18 inch long  "manifold" and then attach the Gorton  on a 90 degree (where there is vertical space).
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