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Radiator air vent on a two-pipe system?

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davidski
davidski Member Posts: 11
in Strictly Steam
This is my first heating season with a two-pipe steam system. I have on radiator (horizontally the furthest away from the boiler) that has an air vent attached to it -- the only radiator in the house with an air vent. As I understand it from here and reading Dan Holohan's work, there shouldn't be a need for an air vent on a two pipe system (presuming the main air vent is working properly, which it seams to be).

This particular radiator doesn't heat well (heats at top but takes forever to fully heat), which I presume is a failed steam trap. I'm working on replacing that, but have noticed that when the boiler kicks in that air vent certainly does expel a lot of air. I'm guessing this is also indicative of a steam trap problem (air can't return, so it's using the air vent).

Are there any other explanations for why an air vent would get installed on a two-pipe system? Should I remove and cap off this vent, focusing attention to make sure the steam trap is working correctly? Appreciate the advice!

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  • Jamie Hall
    Jamie Hall Member Posts: 23,330
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    Odds are pretty good that it's a failed closed trap, and some bright soul put the vent on to "fix" it. Which would account for the slow heating. Not only does the vent have to get rid of the air, but the condensate may be building up in the radiator, limiting its capacity.

    Step one would be to replace the trap innard -- no need to replace the whole trap, unless it is something really strange. Then check the pitch of the return line to make sure that condensate can drain freely. Then go from there.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    davidski
  • davidski
    davidski Member Posts: 11
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    Thanks, Jamie! Glad to my diagnosis isn't totally off. Any thoughts on the keywords to search for on SupplyHouse (or other sites) for the parts to cap this off? Do I want to be searching for a vent plug and is there a standard size I should be searching for? A photo of the current vent is attached.



    At the risk of overloading this thread, I think I may have gotten the wrong trap mechanism for my Barnes and Jones trap. The photo below shows the cap of my B&J trap, which has a female thread on the top, while the replacement mechanism I ordered just has a spring at the top and no way to ensure things stay lined up while screwing in the cap. I don't see any other style tops searching on SupplyHouse though. Am I doing this correctly? It was a bear and a half getting cap off and I'd like to get it put back together properly.



    Original cage pictured below:



    Overview of cage cover and proposed replacement parts:


  • JUGHNE
    JUGHNE Member Posts: 11,062
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    Did you get a new extended height cap for the new cage units?

    The spring will hold the unit in place, be sure to clean the seat of old trap body.

    It is suggested to apply anti seize compound to the fiber washer on the cage unit and seat to prevent sticking if you remove it again.

    All rad vents are simply 1/8" NPT, put a brass plug in there if you can find one.
  • davidski
    davidski Member Posts: 11
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    Ah, no, I did not get a new cover/cap for the cage units. I'm not seeing any hits on extended height covers for B&J traps on supply house. Any pointers/links you could send my way to get the right part?

    Anti-seize compound is standing by. I don't want to go through that process of trying to free the cover again if I don't have to! :smile:
  • Steamhead
    Steamhead Member Posts: 16,856
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    Next thing to check is the air venting from the steam mains and dry returns. If that radiator vent is expelling a lot of air, then the air is not being vented from the right place, which is usually near the boiler.

    Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • davidski
    davidski Member Posts: 11
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    I'm in central MA. I've had New England Steamworks out for start of season inspection and a bit of maintenance. I like the owners there -- they've just had a hard time getting good techs and I'm eager to do what I can myself and save a service call if practical.
  • JUGHNE
    JUGHNE Member Posts: 11,062
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    If you try a dry fit, IIRC the spring should have to be compressed about 1/2" to engage the cap threads.

    The spring holds the bottom of the unit against the existing (clean) seat.

    I would anti-seize the cover threads in addition to the fiber gasket, both sides.

    6 point socket works best for these caps.

    Also if the air vent has a float in it, then rotating it upside down will close the port.

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