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Vacuum Breaker on 2-pipe steam boiler?

I have a Weil McLain LGB-9 steam boiler in a shared 15-unit building from the 1920s. I've taken over the boiler this year after realizing how badly it was managed by contractors. I didn't know anything about steam boilers before, but there were tons of problems with it when the contractors were managing it, and I've come to realize in the last year that EVERYTHING was set wrong, starting with the pressure being set more than 10x too high at 7.0psi. Now its working almost as it should at 0.6psi -- heats everyone, almost no water hammer, gas bills are 40% less, mysterious water loss has stopped, but I'm trying to tune up the remaining minor issues. One interesting fact that might help in answering my question below is that NONE of the 60 radiators in my building have steam traps on them; the only traps are the F+T traps at the end of the condensate and main lines in the basement, back to the boiler feed tank. The condensate lines are rocket hot in the basement, but there are also no radiators down there, so the condensate lines heat the entire floor, so I'm planning to just make peace with that.

My question is: the boiler goes into about -0.5 psi vacuum after it turns off at the end of the heating cycle, while the pipes cool off. I was thinking of installing a vacuum breaker on the boiler to prevent that vacuum state, which I hope will help condensate drain more quickly back to the feed tank through the f+t steam traps at the end of the steam mains (and maybe on the condensate lines too, since there are no other traps?).

Does adding the vacuum breaker to the boiler sound reasonable?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    What, if anything, do you have in the way of main vents for the steam mains? They should open on a vacuum, unless they are one of the few older designs which are intended to NOT open. Before you add a vacuum breaker, check on that. If you do decide to add a vacuum breaker, make sure that you get one with a very low cracking pressure.

    I'm interested in the screaming hot condensate lines -- can you post a picture of the outlet for a typical radiator? There may not be a trap -- but there may well be a special fitting intended to prevent steam from passing through provided the pressure is low enough. Condensate lines should never have steam in them...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GBC_illinois
    GBC_illinois Member Posts: 104

    What, if anything, do you have in the way of main vents for the steam mains? They should open on a vacuum, unless they are one of the few older designs which are intended to NOT open. Before you add a vacuum breaker, check on that. If you do decide to add a vacuum breaker, make sure that you get one with a very low cracking pressure.

    I'm interested in the screaming hot condensate lines -- can you post a picture of the outlet for a typical radiator? There may not be a trap -- but there may well be a special fitting intended to prevent steam from passing through provided the pressure is low enough. Condensate lines should never have steam in them...

    Hi Jaime, thank you for taking the time to analyze my question! We have no vents on the steam mains, only on the condensate returns, I attached pics of those just now. Also, many years ago there was a different boiler, so I'm not sure what type of operation was intended back then. Presumably it was gravity feed, I believe, rather than pumped return.

    RE: Low cracking pressure: here's the one I was planning to get: https://www.supplyhouse.com/Watts-0556031-3-4-LFN36M1-Lead-Free-Water-Service-Vacuum-Relief-Valve

    I've also attached photos of a typical radiator, and of my temp reading on a condensate line several minutes after the boiler had shut off, showing 201 Fahrenheit; they are hotter when the boiler is on.






  • clammy
    clammy Member Posts: 3,111
    That looks like a inverted bucket trap , they do not vent much air . I have seen them used w a standard radiator trap tee off above and used to vent air back into the traps outlet piping w a check valve kinda odd and old set up . From the looks of it you should remove any drip caps and ensure there not clogged if they are then disassembly those inverted bucket traps and clean . Is your condensate pump tank vented and is the common return to it below the tanks water level if so then there’s a water seal on those dry and end of the main returns with not much to aid in venting . What’s your b dimension ,the condensate tank feed pump may not have been totally necessary you may have just needed more boiler water volume to keep the boiler w water on long calls for heat or they used it to resolve running the boiler at high presssure . I would wonder if the original system was completly gravity and through a bunch of knuckle heading ended up where it is . Check those mud legs on the drips . Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    GBC_illinois
  • GBC_illinois
    GBC_illinois Member Posts: 104
    Also Jaime, to your comment about the possible fittings in the radiator returns to prevent steam, I am aware of some of what you might be describing, but I haven't found evidence of those (or at least, I dont know what I'm looking at if I do). Back when we ran at 7psi, it was common for those residents who had their radiator thermostats turned off to still have hot radiators, because steam would come up the condensate side. So, I do think its possible that those fittings you describe were part of the original installation in 1920, I think that over time as radiators have been repaired etc, most of those fittings are gone or no longer functional.
  • GBC_illinois
    GBC_illinois Member Posts: 104
    clammy said:

    That looks like a inverted bucket trap , they do not vent much air . I have seen them used w a standard radiator trap tee off above and used to vent air back into the traps outlet piping w a check valve kinda odd and old set up . From the looks of it you should remove any drip caps and ensure there not clogged if they are then disassembly those inverted bucket traps and clean . Is your condensate pump tank vented and is the common return to it below the tanks water level if so then there’s a water seal on those dry and end of the main returns with not much to aid in venting . What’s your b dimension ,the condensate tank feed pump may not have been totally necessary you may have just needed more boiler water volume to keep the boiler w water on long calls for heat or they used it to resolve running the boiler at high presssure . I would wonder if the original system was completly gravity and through a bunch of knuckle heading ended up where it is . Check those mud legs on the drips . Peace and good luck clammy

    Thanks for your analysis @clammy. Here are my responses to you:

    RE: "Inverted bucket" traps? Here's the model of the traps: https://athena-supply.com/products/illinois-watts-series-g-float-thermostatic-steam-trap . They look like inverted buckets when I opened one up, but the spec sheet says F+T.... so I'm not sure? These are only a year old as they are one of the first things I replaced when I started investigating this boiler's issues. Oddly, when I opened an old one up, there was no gunk inside, clean as a whistle.

    RE: "Remove drip caps" for cleaning: do you mean the downward facing caps on the main and condensate lines, right before the steam traps? If so, I've wondered about these. I've never taken the cap off but it seems they should be cleaned at least yearly. Sounds like you agree?

    RE: Condensate tank vented: Yes, there is a pipe coming off of it vertically about 6 feet and then looping back down, open to the atmosphere.

    RE: Common return below water line? No, its above the water line usually unless the tank is full to the top, which only happens by manual addition of water.

    RE: "B" dimension and possible gravity return: I don't yet know how to measure the B dimension, but I'm reading Dan Holohan's excellent book on it. I am nearly 100% sure that the system used to be gravity return, but when they replaced the original boiler with this one, the contractors decided to put in the tank and pump to charge us more, and have something they can control themselves rather than taking the time to understand the gravity return setup. I have studied the water usage of the boiler during its cycle and how quickly condensate returns to the tank, and the tank sight glass rarely goes below 90%, even on long cycles, without any addition from the tap. So I hope to return it to gravity return operation some day, but I am thinking this will be an expensive re-piping job and the rest of the condo board may not want to "fix something that isn't broken". Do you think it would be expensive to return to gravity feed?

    Thanks again for your expertise!
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    There's another possibility besides odd devices on a radiator return -- although it might be interesting to take one apart and see if those return elbows are as innocent looking as they appear. There might also be, or have been, flow control orifices in the inlets or inlet valves.

    I have a suspicion that what we are looking at here is a vapour system which has been sadly misunderstood and mishanlded over the years. The presence of those beautiful big vents on the dry returns -- for so they are, well above the water line -- suggests that very strongly.

    Two fundamental things have probably happened to this system: first, someone installed a new boiler and failed to match the water line of the old one, happily drying out some or all of the wet returns. Then someone decided to crank up the pressure...

    I honestly doubt that adding a vacuum breaker is going to make any difference at all. Probably won't actually hurt anything, but I don't see anything in your various comments which suggests you need one.

    I agree too with @clammy -- those blue things look much more like bucket traps than F&Ts. You do need either one or the other, since you clearly have steam in the returns where it doesn't belong, but they do work differently.

    Do you have any way of running the system at an even lower pressure? Like a vapourstat? I wonder if the steam escaping into the returns -- which is a problem, though it doesn't seem to be giving you much trouble at the moment -- could be reduced by doing that.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GBC_illinois
    GBC_illinois Member Posts: 104

    There's another possibility besides odd devices on a radiator return -- although it might be interesting to take one apart and see if those return elbows are as innocent looking as they appear. There might also be, or have been, flow control orifices in the inlets or inlet valves.

    I have a suspicion that what we are looking at here is a vapour system which has been sadly misunderstood and mishanlded over the years. The presence of those beautiful big vents on the dry returns -- for so they are, well above the water line -- suggests that very strongly.

    Two fundamental things have probably happened to this system: first, someone installed a new boiler and failed to match the water line of the old one, happily drying out some or all of the wet returns. Then someone decided to crank up the pressure...

    I honestly doubt that adding a vacuum breaker is going to make any difference at all. Probably won't actually hurt anything, but I don't see anything in your various comments which suggests you need one.

    I agree too with @clammy -- those blue things look much more like bucket traps than F&Ts. You do need either one or the other, since you clearly have steam in the returns where it doesn't belong, but they do work differently.

    Do you have any way of running the system at an even lower pressure? Like a vapourstat? I wonder if the steam escaping into the returns -- which is a problem, though it doesn't seem to be giving you much trouble at the moment -- could be reduced by doing that.

    RE: "Suspicion about formerly a vapor system": I agree with you. Another fun fact, I've found an old disused steam main that leads outside the building. The city I live in had an old steam plant about 1/4 mile away many years ago, and I suspect at the beginning, we got our steam from them. Why else would a steam main lead outside?

    RE: "Misunderstood and mishandled over the years": I agree too. What I've realized is that a shared condo building with a boiler system like ours, where no one is really "in charge", cannot just call random HVAC contractors to fix heat issues. They won't understand how the totality of the system works, and will just try to replace a part or change a setting to satisfy whatever the call concern was and collect the $. I have no clue how we got up to 7psi, but looking back through some old invoices from contractors, I suspect that over the years, residents called with complaints of being cold, and the unfortunate so-called "solution" was to turn up the pressure.

    RE: "Can we run at even lower pressure?" Maybe, but I think I'm approaching the brink, given the roughly 250' of pipe length to the farthest radiator, which I've measured out. According to what I've read from the Dan Holohan book, this probably means I need at least 5oz of pressure, and the bottom of my differential is already near that. I currently have a vaporstat control, but its the 5 psi one. We had a Pressuretrol before, but once I realized we could run at much lower pressure, I changed it out for this 5psi Vaporstat, because I was worried about getting the 1psi version just in case we needed to increase pressure. Now that we have history of everyone being well-heated much below 1psi, I'm planning to eventually get the 1psi Vaporstat to have finer control. Any decrease in pressure is a tough thing to test, because I have to survey the other residents about their heat to make sure the new lower pressure didn't stop their radiators from working.

    I did notice that when I formerly ran the boiler at around 1.5psi, and even with my F+T (or bucket, whatever they are) steam traps, I had steam billowing out of the tank vent, but that has ceased now at 0.6psi.

    Good to know that you don't think the vacuum breaker will hurt, I might try it anyway.
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    Condos are a bear. I'm glad you are taking it on -- brave man. To sort of encourage you: you seem to have gotten it to the point where it is working, and people are happy, and you're not losing much water. It may not be working as it was originally intended to, but there is much to be said for taking a step back, once it's working at least, and doing other things with great deliberation and thought.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    GBC_illinois
  • Pumpguy
    Pumpguy Member Posts: 654
    Have you had a problem with the vacuum in the boiler pulling water from the vented boiler feed tank and overfilling the boiler and maybe header too?

    The way this is piped, this would certainly happen when a vacuum develops in the boiler.

    Are you sure you get this vacuum happening and your gauge is reading correctly? The usual gauge for the boiler would be a 30-0-15 compound vacuum pressure gauge, and a 0-3 PSI or less gauge piped in parallel for setting your vaporstat.
    Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
    Website: www.nashjenningspumps.com

    The first step in solving any problem is TO IDENTIFY THE PROBLEM.
  • GBC_illinois
    GBC_illinois Member Posts: 104
    Pumpguy said:
    Have you had a problem with the vacuum in the boiler pulling water from the vented boiler feed tank and overfilling the boiler and maybe header too? The way this is piped, this would certainly happen when a vacuum develops in the boiler. Are you sure you get this vacuum happening and your gauge is reading correctly? The usual gauge for the boiler would be a 30-0-15 compound vacuum pressure gauge, and a 0-3 PSI or less gauge piped in parallel for setting your vaporstat.
    I’m actually not sure the vacuum causes any problem at all; I just have a hunch that perhaps it slows the condensate from draining back to the tank after the boiler shuts off. As far as I know, it can’t pull water from the feed tank automatically, since there is a pump in between. 

    The gauges I have do clearly indicate a vacuum, but even if they didn’t, another way I’ve verified this is by opening the sightglass blowdown valve. Normally, this would drain the water out of the sightglass (onto the floor, in our case), but during the vacuum condition, it sucks air up into it and prevents the glass from draining, sounding like someone drinking the last sips of water through a straw. 
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    If it ain't broke, don't fix it.

    On the condensate returning to the tank. Unless condensate is actually hung up in the piping somewhere, this should not be a problem. The pump from the receiver should be controlled by the boiler water level only -- not the level in the condensate tank (if it's controlled by the condensate tank, that's bad). If that is so, the boiler water level is not affected by condensate return time.

    Additional makeup water should be controlled by the condensate tank level, and should go into the condensate tank. There should be an overflow on the condensate tank as well as the vent on the tank.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 16,830
    1- This is some sort of orifice vapor system. The original radiator valves had restrictors (orifices) which would keep the radiators from completely filling with steam as long as the boiler pressure was kept low enough. You mention that at least some of the radiators have thermostats on them- if these are part of the shutoff valves, you probably need to add orifices. Tunstall makes them.

    2- Those are definitely Illinois F&T traps, as mentioned earlier. The thermostatic portion is under the cap on the top.

    Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    GBC_illinois
  • GBC_illinois
    GBC_illinois Member Posts: 104

    If it ain't broke, don't fix it.

    On the condensate returning to the tank. Unless condensate is actually hung up in the piping somewhere, this should not be a problem. The pump from the receiver should be controlled by the boiler water level only -- not the level in the condensate tank (if it's controlled by the condensate tank, that's bad). If that is so, the boiler water level is not affected by condensate return time.

    Additional makeup water should be controlled by the condensate tank level, and should go into the condensate tank. There should be an overflow on the condensate tank as well as the vent on the tank.

    It is as you say: Pump is controlled by boiler water level only, and makeup water is controlled by condensate tank level. Perhaps the vacuum breaker will have no effect (my guess is 60% likely it won't), but I've become obsessive about perfecting the boiler's operation, and I want to ensure that the condensate drains as quickly as possible. If it doesn't help, I'll return it :-)
  • GBC_illinois
    GBC_illinois Member Posts: 104
    Steamhead said:

    1- This is some sort of orifice vapor system. The original radiator valves had restrictors (orifices) which would keep the radiators from completely filling with steam as long as the boiler pressure was kept low enough. You mention that at least some of the radiators have thermostats on them- if these are part of the shutoff valves, you probably need to add orifices. Tunstall makes them.

    2- Those are definitely Illinois F&T traps, as mentioned earlier. The thermostatic portion is under the cap on the top.

    Where are you located?

    Thanks for your analysis, @Steamhead. I believe that ALL the rads have thermostats on them, mostly this model: https://www.supplyhouse.com/Danfoss-013G8252-RA-2000-Operator-Valve-Mounted-Dial-w-Remote-Sensor

    Any reason why we need to add orifices, if the radiators are heating fine? I know the condensate line should not be filled with steam and hot, but if it was not, we would need to find another solution to heat the basement. So it seems like unless the steam-filled condensate line is causing a specific issue, I'd rather leave that alone. I have turned down the boiler pressure to such a low level that I believe it is not *as* filled with steam as it was.

    I'm in Champaign, IL, a 15-unit residential coop building built in 1920!
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,516
    @Fdarby82

    Make sure the vacuum breaker you use either a swing check valve (Y pattern) or you can get steam vacuum breakers from Tunstall Associates, Chicopee, MA.

    I am not sure the Watts vacuum breakers are steam rated
    GBC_illinois
  • dopey27177
    dopey27177 Member Posts: 887
    Those green steam traps have or should have thermostatic element on the top.
    Look at the hex nut on the top of the trap. That location is the air vent portion of the steam trap.

    \If the boiler is operating OK and water is drawn out of the condensate receiver the vacuum of .5 inches is not a problem. Do not fix what does not need fixing.

    As to the vacuum breaker any quality check valve can be used to break the vacuum.

    If you install te check valve or a boiler vacuum breaker run pipe from the outlet of the fitting to a pail on the floor. Some times the devices leak a bit so te pail will keep the water form wetting the floor. More importantly by running the drip pipe to a pail you be assured that if the device fails steam or water will flow oto any electrical controls.

    Jake
    GBC_illinois