In-Line Vent vs. Air Admittance Valve?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by dzd9fy, Jul 8, 2010.

  1. dzd9fy

    dzd9fy New Member

    Messages:
    27
    Location:
    Michigan
    What is the differnece between these two, and what is the recommended use for an S trap in a basement lav? I am looking at the Oatey 3901 In-Line and the Oatey 39016 AAV if that helps..... Thanks!!
  2. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    If you have a S trap there is no point in venting it anyway.
  3. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    The 3901 is just an air admittance valve, el cheaop version. Make sure if you put on ANY aav that it is installed vertically.
  4. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    Where would you put a vent on an S trap that would make any difference. If you vent the lateral that it dumps into it still has no effect on the S trap siphoning. If you put it at the only place that would prevent siphioning, which would be the crown of the trap, then you have an illegal crown vent.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    They are essentially the same, regardless of what they call them. You CANNOT vent a true "S" trap. You can only use an AAV to keep a "P" trap from becoming an "S" trap.
  6. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,358
    Location:
    Yakima WA
    S straps are illegal under every code, the reason being, they are not vented.
  7. dzd9fy

    dzd9fy New Member

    Messages:
    27
    Location:
    Michigan
    Ok, thanks for the clarification on the differences between the two.

    I am a bit confused on the comments that since it is an S trap it cannot be used, so looking for some insight here. Given the trap is where it is, has worked well for the past 10 years we have been here and guessing since the house was built [1950], what is the suggestion since this is burried under the cement?

    Also, how and why would one use this valve vertically on a P trap? That makes absolutely no sense to me....
  8. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    S traps used to be used, but are very prone to the trap siphoning dry, so are not allowed today. To install the aav, you could possilby santee off the vertical, turn up with an elbow, and put the aac there. Being below the flood rim, this could be problematic. Maybe a wye and a 45 to take if vertical? I would be interested in an inspectors take on this,
  9. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    The only way to do it and be compliant would be to come vertical out of the floor into a sanitary tee with the aav on top of the tee and a P trap into the fixture. As long as the S trap remains there is no code compliant way to vent it.
  10. dzd9fy

    dzd9fy New Member

    Messages:
    27
    Location:
    Michigan
    ok..... so should I just leave well enough alone? It has been working fine, I was just thinking this would be something that would be a good improvement to a less than ideal, and now not permitted use.

    Thanks guys!
  11. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    Yep, let it be. If you notice any odor, run a bit of water in the sink. called priming the trap in the old days.
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