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Reccomended Pressuretroll Settings

I adjusted the 2nd (right troll in attatched pic, avatar pic is our boiler) pressuretroll top screw before looking at what the setting was at historically, and am now wondering what the best setting should be for each for our single-pipe steam boiler. We can also make adjustments per the prior reccomendations, but haven't gotten to that yet due to water heater replacements being a priority recently. The left one looks like about 1psi cut in with a 1 psi differential on the wheel inside, and the right one is at about 2 psi cut in with the same 1 psi differential. Any thoughts on adjusting them further?

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,253
    They look like their wired in series...are they????1 could be an operating control and 1 could be a high limit control.

    Or 1 could be lo-hi fire and 1 could be a limit control.

    Look for model #s on the controls and how they are wired. Then we can determine what they do. Are they both PA404A??
  • cubicacres
    cubicacres Member Posts: 329
    edited January 2018
    With the 3 pictures attatched, they look like the same model to me. I think like our old boiler, one was the operating control & the other the higher limit control? I think that's considered series if on the same line, one a bit higher than the other per the photos.

    For our background understanding, does the one on the left just above the pigtail (higher up, closer to the boiler, first "in-line") let the boiler fire above 1psi cut-in and with the 1 psi dial setting turn off the boiler at 2 psi when vents have closed? And if this one fails, does the other one act as a backup at 3 psi cut-off with the same 1 psi differential dial setting & 2 psi cut-in selected with the top-screw?

    Why bother with a low pressure cut-in setting at all, instead of just a high-pressure cut-off?

    Does cutting off when pressure builds stop the boiler from running wastefully? We saw pressure reach about 3psi then seem to shut off on low water or pressure, but we couldn't be sure what cut it off. The tekmar told us the room was warm enough at that point, so maybe adding pressure to the system doesn't give more heat to the rooms anyway (or would make them overheat)?

    I think we'd want each troll to have a seperate pigtail as well?




  • Jamie Hall
    Jamie Hall Member Posts: 17,047
    Well let's see here. Seems to me we've been here before...

    First off, the pressuretrol (or 'trolls) are really safety devices. In most systems, however, they serve to shut off the pressure when the system is full of steam and delivering all the heat it can; no point in running the boiler after that. So, typically, the main (or only on many systems) pressuretrol is set to cut off the boiler at around 1.5 psi, and cut back in at around 0.5 psi. Or slightly higher. That would be the one you have set at a 2 psi cutout right now. The other pressuretrol is very much a safety device, and will cut the boiler off above some higher pressure -- in your case, about 3 psi.

    The reason for a separate cut in, or differential, is that there must be a difference between where the pressuretrol cuts off and where it cuts in. Otherwise, when it cut off and the pressure drops even a little tiny bit it would cut right back in, which is hard on the equipment.

    That help?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Fred
    Fred Member Posts: 8,518
    It would seem to me that if they are wired in series, if one fails to open on higher than set pressure, the other would trip and shut the boiler down. If that's the case, then I would expect both to be set for Cut-In at .5 PSI and one (either) can have a Differential of "1" and the other a Differential of maybe 1.5. Actually both could be set exactly the same, if so desired.
    The one issue I see is that they are both tied to a common pigtail so if that pigtail gets clogged, neither will cut out or possibly even cut-in. Each should be on separate pigtails, on different tappings.
  • cubicacres
    cubicacres Member Posts: 329
    edited January 2018
    Thanks. We did intend on measuring them & checking our gauge per the last post reccomendations (and getting a 2nd pigtail the installers took back with them before we knew as much), but adjusted the higher safety one on the right before we could get to that & got concerened when the screw came off the top without us remembering what it was set at. We just set it 1 psi higher then the one on the left at 3psi cut out with a 1 diff. for now.

    If our tekmar is showing the indoor sensor is keeping the room warm enough at 1.5 psi, does that extra few minutes of run time that moves the pressure up to 2.5-3psi range before it shuts off (on low water or pressure-we're not sure) just compact the steam in the lines & "waste it" if the vents are already closed? Is this the efficiency idea of keeping it as low pressure as possible(minimal burner run time to provide adequate heat to the rooms)?


  • Jamie Hall
    Jamie Hall Member Posts: 17,047
    You got it...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England