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Radiator Vents and traps

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Disclaimer: We don’t do a lot of stream in the Midwest. A fair amount of hot water but not steam. I was following up a noise and flooding complaint. Manual filled system. Owner’s wife flooded it. We did a tune up on the boiler. Owner thought it was still flooding and some noise. I went back and flushed the 2 return drops and checked the main steam vents. Looking at the rads I noticed all but 1 downstairs and only 1 upstairs had steam vents. I thought it was odd. In my brain fart it didn’t click that this 2 pipe system should have traps. It’s not a large house, maybe 1200sq ft. I’m going back to see if there are in fact traps. Guessing maybe previous contractor added vents to make rads heat better (?). Thoughts on having both in the system. Assuming there are traps should I plug the vents and replace the traps? How best do you determine which traps are bad? Thanks for any assistance.

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  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,529
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    @Cheeze-Tech

    It's possible if they flooded the boiler they forced water into some of the vents.

    Two pipe steam is basically done 1 of 4 ways

    traps and no air vents on the radiators (most common)

    Orifice in supply valves to radiators and no traps

    Air vents on radiators and no vents (two pipe air vent system)

    No traps and no vents with a special elbow on the return connection of the radiators

    Traps can fail open or closed although failing open is more common.

    Failed closed =cold radiator, cold trap, no heat

    Failed open= plenty of heat hot trap stem in the return lines

    You should see some temperature drop from the trap inlet to the trap outlet

    Many times a radiator with a failed trap will seem fine but it will pressurize the returns and may cause other radiators not to heat and cause noise and hammering


    Cheeze-Tech
  • MilanD
    MilanD Member Posts: 1,160
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    Not enough info to accurately assess the situation.

    Is the system working fine? What's the ok pressure set at? Are there crossover traps in basement? 

    There are several 2 pipe setups. Old old ones are in fact 2 pipe vented (1900s). Returns should all drip onto a wet return, individually. Newer ones are trapped (1920s and on, roughly) and would usually have crossover traps too. There are also some that are not trapped at the radiator, but have orifices installed on the supply valve to regulate steam flow and allow for all steam to condense before reaching the return, so no need for traps even though it's a 2 pipe.  

    Vent that's missing could be legit missing (like someone plugging it bc old one dripped). Or someone added vents where there shouldn't be any, so... Anything is possible.

    Where are you in Midwest?
    Cheeze-Tech
  • Cheeze-Tech
    Cheeze-Tech Member Posts: 84
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    MilanD
    The house was probably built 1920-1950. Dry returns. Like I said after I left my brain said “what?!?” I’m going back to take a closer look to see if there are actually traps on the radiators too. Any way to tell if there are orifices or just the lack of a trap? “Crossover trap”? They look like a radiator trap but on the mains? I believe steam pressure is 1/2# ish. Boiler was replaced in early 1990’s. Any potential issues if vents on rads with traps? Located in Southern WI.

    Somewhere I’ve got “The Lost Art of Steam”. I’ll have to dig it out. Forgot I had it.

  • Jamie Hall
    Jamie Hall Member Posts: 23,313
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    Crossover traps do look like radiator traps. In fact, as often as not they are radiator traps! Just piped so that they take off from the top of the steam main, turn and go over to the inlet of the trap, and then back down to the dry return. There is almost always also drips from the dry return and the steam main to an associated wet return -- although now and then you'll just see a water seal loop down to the floor and back up.

    There really isn't much harm... sort of... to having vents on the radiators or some of them, as well as traps or orifices -- except for two things. First, they can make balancing much harder than it needs to be and second, in some systems which do have crossover traps, there must be one -- and only one -- vent location closely associated with the boiler; additional vents will defeat part of the system operation.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Cheeze-Tech
  • MilanD
    MilanD Member Posts: 1,160
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    @Cheeze-Tech

    Your best bet is to dig out the Art of Steam Heat. Most if not all info you'll need is in there. The rest is like @Jamie Hall" said. Good luck! 
    Cheeze-Tech
  • Cheeze-Tech
    Cheeze-Tech Member Posts: 84
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    Stopped back by and did some investigating. No traps seen anywhere. Nothing on the main either. Assuming orifice system. One rad valve has been replaced. The rest look to be original. Found my lost art book which has been floating around long enough it’s become a loose leaf folder. I can take out any page I need to. I’ll do more reading tonight. See attached photos and give me any thoughts. I am trying to get educated. Appreciate your responses. Main splits in two directions, ending at a radiator. 2 pipe steam with no traps and some vents has me puzzled. A couple rad need to be repitched toward drain line. Ran boiler for 20-25 min with minimal noise. How long does it take to get condensate to flow? Pressure set at 1-1 1/2 psi.






  • MilanD
    MilanD Member Posts: 1,160
    edited January 2021
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    Now, I don't think I ever saw a 2 pipe vented system with dry returns.

    Then, whoever piped this boiler didn't bother reading the instructions. Maybe can't read, period. I don't even know what that Hartford loop does... Everything is backwards. Goes to show how forgiving the steam can be... 

    System works silently? Heats up fine? Water not going wild in the sight glass? 

    Perhaps with so little venting it gets to higher op pressure quickly and that slows down steam velocity and allows the system to work despite the lack of header. It'd be interesting to see a low pressure gauge on that.

    What is this EG30? That's small. 

    If everything works fine, put your hands in your pockets and don't touch anything. Just service lwco sensor, and if over 10 yo replace it. And make sure water fill valve doesn't leak. (it's manual feed, right?)

    Other than it being flooded, any other issues? When you say "minimal noise", what do you mean?
    Cheeze-Tech
  • Cheeze-Tech
    Cheeze-Tech Member Posts: 84
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    As far as noise that’s a good question. I watched it 20-30min and heard maybe 3 clanks. Like hitting a pipe with one of those tiny hammers that comes in a homeowner all in one tool kit. She said they had been there 24 years and thought it was fairly quiet. She did mention something about it occasionally sounding like a wrench hitting a pipe, but thought it was quiet. Sometimes guests are surprised by the noise. I think they have just gotten used to it. I didn’t think the piping looked right but I had not installed one hadn’t looked up a manual yet. I’m familiar with the Hartford loop and didn’t think it or the supply was right. So what about the combo of vents/no vents. If the near boiler piping was correct would the main return vents be the only ones needed? They know the boiler is nearing the end of its life so we’ll look to correct it on the next one. Pressure gauge showed it shut off at around 2 - 2 1/2# after 20-25min.
  • Jamie Hall
    Jamie Hall Member Posts: 23,313
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    The little clinks and clanks are almost certainly something expanding and shifting. One does get used to them pretty fast -- and they can be remarkably hard to get rid of!

    If a two pipe system is piped correctly, the only vents needed are on the dry returns at the boiler -- which are really needed, and it pays to have them good sized -- and at the ends of the mains, but only if there are no crossover traps. If there is the odd radiator piped as a one pipe radiator (it happens) then that does also need a vent.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Cheeze-Tech