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one pipe job

928 Member Posts: 3
ok I am not going to give up ! working on a low psi one pipe steam job in Phila

new boiler all new one pipe adjustable (Heat-Timer Vari Valves) steam vents.

I have the pressure as low as the Honeywell control will allow (it came with the boiler)  I tried to use a Vapor Stat because that is what Dan will say to use however this is where I am FUZZY. The Vapor Stat is a Honeywell L408J-1009 Main scale 0-16oz  differential scale from 2-16oz. I feel like a dummy because I can not figure out this subtractive part. I tried numerous combinations and could not prevent the boiler from short cycling.  All the radiators are pitched. Also replaced the main steam vent at end of main. Any help would be greatly appreciated



  • Paul48
    Paul48 Member Posts: 4,469
    edited March 2013

    How well is the boiler sized for the system? It may be new, but is there enough main venting?
  • Jamie Hall
    Jamie Hall Member Posts: 19,139
    They can be tricky.

    Setting a vapourstat is not a problem; the main scale sets your cutout, and then you subtract the differential scale setting from that to get the pressure at which it will cut back in.  For example, if you main is set at 12 ounces, and the differential at 4, it will cutout at 12 and cut back in at 8.

    Now comes the interesting part: in some installations, it may be necessary to install a snubber (I forget where I got mine...) just underneath the vapourstat, as vapourstats are more sensitive to brief pressure fluctuations due to bubbles bursting and the like than are pressurestats.

    And, as Paul notes, how's your venting?  And how well is the boiler sized to the load?  Weak venting can cause problems early in a cycle, but if the short cycling is only happening towards the end of long run -- say coming out of a setback -- it is probably slightly oversized.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 928
    928 Member Posts: 3
    one pipe steam

    that a good call. only one main air vent and I think the boiler is over sized. I am going to get the EDR and show contractor my findings
  • 928
    928 Member Posts: 3
    one pipe job

    only one main vent and I think the boiler is over sized for the radiation. I am going to measure the EDR. I am helping a contractor out. I did have him install all new one pipe steam vents (Vari-Valves) and I do have snubbers I will try it now that I have a better understanding of how to adjust the VaporStat

    Thank You
    STEAM DOCTOR Member Posts: 1,500
    one pipe

    The vaporstat may not be the problem(as mentioned). There are many things that can cause excess pressure with will lead the stat to do its job(i.e. shut the burner when the pressure is too high). Bullhead T's can cause increases in pressure. Undersized near boiler piping can cause too much pressure. An oversized boiler can cause too much pressure. Inadequate venting can lead to higher pressure. A 0-3 pound gauge would be a great idea. On a different topic vari-vents are ill advised. The high venting rates can lead to some radiators hogging steam from other rads.In addition they preform poorly in holding back water in wet steam situations(eventhough an air vents job is not to hold back water anyway).
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