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Thread: AAV with basement ejector pump

  1. #1

    Default AAV with basement ejector pump

    I know this is not a popular or recommended set-up but I've inherited it, and I have a problem with it...
    The pump is for a shower. For whatever reason the pump does not use the roof vent that the sink and toilet use.
    Anyway, sewer gas sometimes escapes from the AAV when the pump operates, and I think it only happens if the bathroom door is closed and the extractor fan is running, presumably due to the lower air pressure in the room. I have replaced the AAV twice so it's not a faulty vent.
    The set-up looks like this diagram (from Studor), except that there is no connection between the vent pipe and the drain outlet. My question is, is that significant? Would that make the vent more effective so that we don't have to leave the door open to take a shower?

  2. #2

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    Not sure I subscribe to the lower-air-pressure-in-the-room theory.

    When the ejector pump (not fan) is running, it is pulling air IN from the vent to displace the liquid it's expulsing. You shouldn't get stink from the vent until after it stops and then only if the vent stays stuck open. The churn inside the bin can cause some stinky air to be pushed out of crevasses in the lid during flushing or ejecting if it's not properly sealed.

    I think you only notice it when the door is closed bkz the stink doesn't diffuse and escape the room.

    I'd check that the lid is sealed and that the vent operates. You shouldn't need a loop from the discharge back to the vent port. Such a vent would not assist the pump in displacement. I think that vent is only there to prevent bypassing drainage from siphoning out the column of water that holds the check valve shut. But if you have a good cv, you shouldn't need that column anyway.
    (important note: I'm not a pro)

  3. #3

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    Thanks for the reply prashter.
    I'm 99% cerain that the problem occurs only when the bathroom door is closed - the smell is very noticeable around the whole area if you open the door afterwards so I don't think there's any way we could miss it.
    I agree that it doesn't seem right that an extractor fan would cause enough of a pressure differential to pull gas back out of the vent. I guess there could be a leak around the lid so I'll check more carefully.

  4. #4
    Master Plumber master plumber mark's Avatar
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    Talking vapor locking air vents.....

    the problem is that auto air vent on
    the sewage pump
    it just wont ever work right


    you might say that the pit is "vapor locking "
    (my technical term) when it has to pump out
    the sewage,,,,, it is sucking down on that auto air vent
    and not able to get enough air,

    so its probably siphoning the trap to the shower or lavatory....


    the only solution
    and if you could even run something as small
    as a 3/4 pvc inch pipe up to tie into the main stack vent
    or get a pipe outside the back of the house
    ( of course the bigger the pipe the better)

    to equalize the atmoslphere in that pit
    the problem will never return.....

  5. #5
    DIY Member pump's Avatar
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    Default

    I will have to agree with Master Mark on this one about the mechanical vent not ever working right!

    With all of our pump systems, we never, ever recommend a mechanical vent with any of them!

    ZP

  6. #6

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    It's a Zoeller pump by the way...

    The gas is definitely coming from the pump/AAV area, not from any of the other traps. It's in a closet so there's no mistaking the source.

    Is it conceivable that the difference in pressure between leaving the door open or closed affects the operation of the AAV?

    (BTW, I realise no one would never recommend this set-up, I'm just trying to explore all options...)
    Last edited by Chippy; 10-24-2006 at 01:14 PM.

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default pump

    1. The only pressure differential that would affect the AAV is if the room were at a higher pressure then the valve would open. A lower room pressure would force it even tighter closed.
    2. If the connection were made between the discharge and the vent, the water would just circulate in a circle.

  8. #8
    In the Trades kordts's Avatar
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    Default

    What part of it's the AAV don't you understand?

  9. #9

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    When the smell is bad, do you notice that the traps are dry? If yes, then MPM has to be right. If no, then MPM, doesn't that conflict w yr conclusion?
    (important note: I'm not a pro)

  10. #10

    Default

    No, traps are definitely not dry, I don't think Mr smartass kordts wants us to discuss the subject any more though. Too bad, I'm still kind of interested in why leaving the door open seems to make the system work
    (kordts - I KNOW it's the AAV, a-hole, that's why it's in the subject)

  11. #11
    In the Trades kordts's Avatar
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    Hey Chimpy,
    nice mouth, ya kiss yer kids with that? I am merely trying to reinforce the good advice given that an AAV on your installation won't work. You need to install a VTR. Lose the 'tude, Chimpy.
    Last edited by kordts; 10-26-2006 at 08:55 PM.

  12. #12

    Default

    Best to ignore comments you perceive as smartass. Nobody wins.

    Anyway, I'm puzzled now. IMHO it seems like it's not a vaporlock problem, else you'd have some dry traps.

    Have you tried sealing the lid better?

    When I first installed my basement 'pit, I left the lid off for a few weeks to observe and test. I noticed that whenever something was added to the pit, the odor was stirred up. Even if you just used the sink. That's what makes me think it's a lid-seal problem for you...
    (important note: I'm not a pro)

  13. #13
    Plumber Cass's Avatar
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    Quote Originally Posted by prashster
    Best to ignore comments you perceive as smartass. Nobody wins.

    Anyway, I'm puzzled now. IMHO it seems like it's not a vaporlock problem, else you'd have some dry traps.

    Have you tried sealing the lid better?

    When I first installed my basement 'pit, I left the lid off for a few weeks to observe and test. I noticed that whenever something was added to the pit, the odor was stirred up. Even if you just used the sink. That's what makes me think it's a lid-seal problem for you...
    If the lid is sealed then the AAV won't work right. If the lid is not sealed the AAV still won't work right. A sewage ejection pit must be vented to the atmosphere outside the home through the existing vent system or by its self.

  14. #14

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    Quote Originally Posted by Cass
    If the lid is sealed then the AAV won't work right. If the lid is not sealed the AAV still won't work right. A sewage ejection pit must be vented to the atmosphere outside the home through the existing vent system or by its self.
    I understand. But the AAV doesn't appear to be airlocking, as evidenced by his full traps. If it were pulling in air from the lid gaps, then it's unlikely that odor would be emitted from the pit.

    I think he should seal the pit first, try the pump. If then his traps are being sucked, he'll KNOW it's the AAV.
    (important note: I'm not a pro)

  15. #15
    Plumber Cass's Avatar
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    With an AAV installed and the plumbing system air tight when he flushed a toilet the toilet would drain until it (the pit) had enough pressure and it would stop then the water in the bowl would start to back up. If the pump turned on the pit would depressurize and then suck air through the AAV until the pump stopped..

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