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3 Pressuretrols ??


Newbie here, illustrious new President of the Board, trying to understand the steam system in a 25-unit co-op in Toronto, ON, dating from 1925.

We have a Weil McLain 1280 boiler, tended by an honest-to-pete Engineer. The only trouble is, he's a wind-tunnel engineer, not a steam engineer. He's got us running at 7 to 9 psig, because "some of the top floor rad's are cold". I've read Dan's Lost Art book, and a lot of other resources, and I know we can do better than swelter in January and pay through the nose all winter.

I am convinced that 90% of our traps are bad, and I know for sure that a lot of Danfoss thermostats have failed, or are the wrong type for the enclosed cabinets, and/or have been installed in the wrong orientation (vertically, above the supply pipe). Mr. Wind Tunnels is keen and generous, but I am not confident in his work.

I'm trying to understand the controls on the boiler, and I'm confused. There's three Pressuretrols. One, with a mercury switch, is obviously the safety, set for higher pressure. But there's two others, set for different pressures, that both connect to the same gas-burner controller. What's going on here?? Please see attached photos. Pressuretrol #1 is set around 5 psig (I've been cranking it down from the 7-9 range); Pressuretrol #2 is set much lower; Pressuretrol #3 is the safety, set at 12.5 psig. All three controls connect electrically to the gas-burner control. What's the purpose of #2, and why is it set so much lower than #1?

Also, when I turn off the whole system, I hear the sound of running water draining into a floor drain, from pipes that originate at the boiler. This makes me think that the condensate is flooding the boiler and overflowing. (We have a condensate or boiler-feed pump on the system, it's not just gravity return; the condensate receiver is also fed by a water-softener supply, so I think it might be a boiler-feed rather than just condensate. See photo. Note, there's two electric motors/pumps? operating on this condensate receiver -- what's that about??)

Anyone's help greatly appreciated. Any recommendations of steam expertise in Toronto GREATLY appreciated!



  • tim smith
    tim smith Member Posts: 2,498
    Pressuretrols & settings etc

    Looking at the pics helps a little, I would say you should be able to reduce your pressures dramatically. The 3rd pressuretrol is probably for lo hi lo operation of the burner. In other words the one that is set at the lowest range probably is the low fire setting. When pressure reaches it's setting then the burner reduces firing rate to reduce cycling/increase efficiency. My guess is that you are correct that you need to rebuild/replace traps. Main air vents may be bad causing steam to not get to further reaches of system fast enough before rest of system is ready to shut down. This could also explain the flood back of condensate on shut down. Numerous items here to check. Try posting this on the wall above w/ a heading of Steam problems, (your city) help. Good luck, Tim
  • Hi Stuart

    Here's some info (in the second half of the article) that might help.

    The lowest set pressure controller (the low/high fire control) will be the one that has to match the system in your building the closest, as it actually regulates the minimum pressure that it takes to reach every radiator in the coldest weather. Picture the steam pressure rising from a cold start in very cold weather. The pressure will rise to fill the farthest away radiators and keep rising until the low/high fire control flips, and the boiler goes to low fire. Now, under heavy load, the pressure begins to fall and that last radiator or two lose steam, and lose the ability to heat. This would indicate that this controller is set TOO low. Your occupants would notice and tell you about this condition. This control needs to be set such that there is still steam at every radiator when it flips back to high fire, at the bottom of the low fire part of the cycle. It's a pretty fine line. The radiators in question won't become cold, they'll just underperform in the coldest weather, making it hard to troubleshoot. They'll always be the same radiators, though. In this way, they'll be different from trap failure symptoms.

    Once the low/high fire control is set, the high limit control only needs to be set a small amount higher than that pressure, so that the boiler has a small cushion of pressure range to coast into when going to low fire, before the pressure begins to fall again. in low load conditions, the boiler will go to low fire, which is still more than enough fire, and fairly quickly cycle off. It needs to be set high enough only to prevent the off cycle drop in pressure to not trip the low/high fire control back to high fire (meaning that those last radiators have lost steam again) during the burner purge cycle, before it fires back up. Once you find that sweet spot on the pressure cycle, the controls can be set around that number.

    Evaluating a Steam System

  • Stuart Rogers
    Stuart Rogers Member Posts: 48

    Thanks, Tim. I've reposted as you suggested.

    Obviously, I will have to read up on this lo-hi-lo operation -- I have not encountered any mention of it in my readings so far. My guess is it's not operating properly anyway, since the burner has only two states, full blast and off, and the pressure stays only in the 7-9 (now 5-7) psi range.

    Thanks again,
  • Stuart Rogers
    Stuart Rogers Member Posts: 48

    Noel, thanks so much for your reply and the link to the article (I take it you're the author?). I will go over it carefully; I've also had a look at some of the other pages of that site, and there will be useful info there too. As I replied to Tim, I obviously need to gain an understanding of this lo/hi firing business to start with.

    Thanks again,
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