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Matthias Member Posts: 22
Hello Steamheads - I am looking for an answer for this vaporstat movement. Pigtail is filled with water but it's rocking like crazy. The main setting was. At 16 oz and differential was at 16 oz. I changed it to 6 oz main w/ 4 oz diff based on previous threats I read. However, the boiler kept going in and off via the vaporstat. See the video.


  • BobC
    BobC Member Posts: 5,230
    When startung up from a cool boiler, about how long does it take for the vstat to cut out? Then how long does it stay off, and how long does it un before cutting off again?

    If the boiler is oversized it's normal for it to cycles, maybe a minute or two on and then off for a like time.

    Is the pigtail clear?

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Matthias
    Matthias Member Posts: 22
    Thanks for your comment @BobC. It takes roughly 15-20 minutes before vaporstat cuts out. It'll stay off for 15-45 sec and run for a minute or so till it cuts out again. We cleaned the pigtail and primed it.
  • Jamie Hall
    Jamie Hall Member Posts: 17,103
    A low pressure gauge would be very helpful to the diagnosis... I don't see the video, so I would ask: is the movement of the mercury bulb smooth, or is it rather jittery, jouncing back and forth? If it is the latter -- which is not at all uncommon -- it is responding to instantaneous, short term variations in the steam pressure. These occur for any number of reasons, and are unavoidable.

    There is, however, a solution: a pressure snubber. Grainger has them, as do a number of other folks. It would be placed between the top of the pigtail and the vapourstat inlet. A word of caution on them: the filter type, which is entirely satisfactory for the purpose, does have a tendency to clog and should be replaced annually.

    As to the timing of the problem -- both in terms of run time before it starts, and cycle timing after it has started. The run time is good. That suggests you have at least adequate main venting on your system. The within cycle timing, however, tells me that the boiler is significantly oversize for your system -- at least half again as big as it needs to be. You might consider having a qualified tech. down fire it, if that option is available.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 8,959
    This vaporstat had the mercury jiggles also. approx 4-8 oz operation.
    The double pigtail cured it, note the support bracket off to the steam riser. (not my welded header BTY, but no water hammer from the water pocket)
    JUGHNE Member Posts: 8,959

    Maybe a better shot.