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Hoffman no.1 differential loop leaking

Hello all,
Looking for some insight into an issue a friend is having with their steam system. They have a Hoffman no.1 differential loop that is leaking. He had his Plumber come by and put some pipe clamps on to stop the leak. If you're looking at a cutout of the loop like in Dans lost art book, the right side pipe has begun to leak. Right through the wall of the pipe. I suppose my question is, is this repairable? Can I carefully cut both sides of this loop as to not cut the inner pipe and cave out the existing pipe from the top and bottom portions of the loop? Then install new pipe with unions between top and bottom portions of the loop? I haven't seen the system yet. I only have one picture that he sent. Going to check it out this weekend. Wondering if anyone has ever dared to take one apart and make a repair. If you advise against repair, what would a good course of action be to take on this. Please advise. Any information would be very much appreciated. I've attached the only pictures that I currently have.


  • New England SteamWorks
    New England SteamWorks Member Posts: 1,520
    Where is your friend located? Perhaps we can help.
    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems
  • Steamhead
    Steamhead Member Posts: 16,901
    What @New England SteamWorks said.

    If the Loop is shot, the system can run without it if you change the Pressuretrol to a Vaporstat whose maximum setting is 16 ounces.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • plumber6120
    plumber6120 Member Posts: 9
    Thanks for the replies. I've seen both of your work on this site and it's pretty amazing. I'll run it by him. We are in the Ithaca, NY area. Finger lakes area. Might be a long haul for you to get here though. I do plan on helping him with this. I worked on one pipe steam systems in Brooklyn, NY for seven years. Two pipe is new to me but I understand it. I'm going to look at the system this weekend and see what it looks like as a whole. ill post more pictures and questions once I know more. Thanks for the help!!
  • Jamie Hall
    Jamie Hall Member Posts: 23,443
    Steamhead said:

    What @New England SteamWorks said.

    If the Loop is shot, the system can run without it if you change the Pressuretrol to a Vaporstat whose maximum setting is 16 ounces.</blockquote

    Yes you can take those things apart. That is to say, they were screwed together in the first place. However... that was a long time ago, and it may be reluctant, to put it mildly. I think I might be inclined to give that a try -- but if it didn't work you can indeed take it out of the system completely. Run a vapourstat at a cutout of 8 ounces and a differential of 4 ounces (verify with a good low pressure gauge!) and reroute the dry returns directly into the wet return and the boiler. You can take out the steam feed from the header completely. Leave the main vents as is.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England