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why main vent failed again?

bruce_21
bruce_21 Member Posts: 241
I replaced my customer's main vent which was leaking 3 years ago. Now the new one is leaking. What can be going on?It is on the end of a 3" main that is about 85 feet long. What size should I use for the next round? The old one sits on a 4" nipple but the top of the vent is already close to the floor above so I can only add about 3-4 inches to the riser at best.

Comments

  • Fred
    Fred Member Posts: 8,542
    What kind of Main vent do you have on there that is only 3 - 4 Inches?
  • bruce_21
    bruce_21 Member Posts: 241
    Hoffman 4-A
  • Fred
    Fred Member Posts: 8,542
    That's barely a radiator vent at .133 CFM at 1 ounce of pressure. A 3" main, 85 feet long should have 5 or 6 Gorton 2's or 3 Barnes and Jones Big Mouth vents. With such a small orifice, it probably get crap blown into it and can't close. It must take forever for steam to get to the end of that main. Probably half your fuel bill goes towards evacuating air from the main.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,350
    probably 3 things can damage a vent.

    Water hammer
    Dirt
    Running the steam pressure too high
  • bruce_21
    bruce_21 Member Posts: 241
    What is difference between gorton #1 and #2 and B&N big mouth in terms of speed of air elimination? I can't yet find cfm specs on them.
  • Jamie Hall
    Jamie Hall Member Posts: 22,967
    Very roughly a factor of 2 from #1 to #2 and the from #2 to the BigMouth. I personally think @Fred 's recommendation is overkill -- but a couple of BigMouths might be a good idea. They should fit...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Fred
    Fred Member Posts: 8,542
    I don't know @Jamie Hall , 85 ft of 3" main is a lot of air but 2 Big Mouths is certainly a lot better than the one Hoffman 4A on there now.
  • Jamie Hall
    Jamie Hall Member Posts: 22,967
    Fred said:

    I don't know @Jamie Hall , 85 ft of 3" main is a lot of air but 2 Big Mouths is certainly a lot better than the one Hoffman 4A on there now.

    Oh yeah. That 4A might just as well not be there!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 11,021
    What size is the 4" nipple? There is a limit to the air that that the pipe can pass.
    I would put a 90 on that and then add nipples/tees for vents.
    The 90 could prevent debris from getting into the vents.
    The assembly you build needs to slope back to the 4" riser to drain.
  • BobC
    BobC Member Posts: 5,473
    To add some perspective one Big Mouth has about 16 times the venting capacity of that Hoffman 4A. I don't think your plumbing supply will have it so order it through this site or -

    https://www.amazon.com/Barnes-Jones-Big-Mouth-Vent/dp/B01F26P13C/ref=sr_1_1?ie=UTF8&qid=1515068372&sr=8-1&keywords=big+mouth+vent

    That thread is 3/4 inch so you will have to adapt if your dealing with a 1/2" nipple. Also a 1/2" pipe can support only 2 Big Mouths.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Neild5
    Neild5 Member Posts: 163
    At 3 oz
    Hoffman 4A 0.266 CFM
    Gorton #1. 0.700
    Gorton #2. 2.200
    Big Mouth. 3.600
    Open 1/2 pipe. 4.80
    Open 3/4 pipe. 9.00

    These numbers are from the white paper by Gerry Gill and Steve Pajek.
    Circa1902Canucker
  • Shalom
    Shalom Member Posts: 165
    Does anything need to be screwed into the outlet on the side, or just leave it as is?
  • Fred
    Fred Member Posts: 8,542
    Shalom said:

    Does anything need to be screwed into the outlet on the side, or just leave it as is?

    The references given for "Open Pipe" is simply to show capacity. You can not leave the vent pipe on a steam system open. It must have a vent on it that closes when steam hit it.
  • bruce_21
    bruce_21 Member Posts: 241
    Thanks to everyone for the tremendous help!
    I think I will get 2 big mouths and some 3/4 fittings and make a swing joint on top of the 4" nipple so I can counteract the slight pitch of the main to insure these not so cheap vents don't get done in by condensate.
    I saw a picture of the big mouth on a website that shows a 3/4 female opening on the side of the big mouth. Is this what Shalom is referring to?
  • Fred
    Fred Member Posts: 8,542
    That threaded opening on the back side of the Big Mouth is left alone. The body of the Big Mouth is designed for other applications besides a vent.
  • Shalom
    Shalom Member Posts: 165
    Yeah that was what I was asking about. I thought maybe you had to connect a short nipple or something there, so that dust or whatever doesn't get into that side opening.