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Two Pipe Vapor System With Hoffman Differential Loop Valve

I'm replacing an old steam boiler that utilizises a Hoffman Differential Loop valve and piping system. I know that I should leave the Hoffman valve and piping alone since removing it can cause many problems. My question is when tying the condensate line back in do I still use a hartford loop on the new boiler? There appears to be one now, but the condensate line that comes up out of the floor and enters the line that goes to the boiler from the Hoffman valve is quite high. In Dan's book he mentions that we need to lower the water line from the original. If so, do I lower the building condensate line connection to that pipe from the Hoffman valve to the new boiler, in essence making a new hartford loop and lowering the water level or would I make a new Hartford loop on my new boiler by tying the exsiting condensate line from the old boiler into my new equalizer just below the water line,as per the manufacturers recomendations? 


  • Steamhead
    Steamhead Member Posts: 16,728
    edited December 2009
    It might be simpler

    to set the new boiler up on blocks.

    What you're trying to avoid is lowering the water level below the loop seals (points where drips from steam main and dry return are teed together). If you do this, steam can jump from the steam main to the dry return, which will equalize the pressure between the two. If that happens, the radiators will not heat since they will have equal pressure at their inlets and outlets.

    For the steam to move, there must be a difference in pressure. High pressure goes to low pressure, even if the difference is only an ounce.

    Oh, and that buried return line is probably leaking. Replace it.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Jamie Hall
    Jamie Hall Member Posts: 22,932
    Water level

    Do NOT lower the water level.  Do NOT raise the water level.  Set the new boiler on whatever foundation it needs to have its water level at the same height as the original.  I would put Steamhead's comment much more strongly: it isn't that it might be simpler, it is flat out essential that you not lower the water line, as the risk of going below the loop seals is too great.  Further when you raise that buried return line, keep an eye on the loop seals on it.  You do not want to raise the water level, either, as that will interfere with drainage (those dreaded A and B dimensions).

    Do (or don't, as the case may be!) that and all should be well...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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