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Author:
gmum (IL)
This has been in service for 50 years. Both fixutres (in separate rooms) drain quickly. They both connect to same horizontal branch. Each do not have a separate vent however, the horizontal branch connects to the main lateral there is a 4" main stack about 6' away.
When the tub drain, when it empties I get a few gurgles from the sink on that same line. Im thinking adding an AAV to the trap arm on the sink.... is that going to stop the gurgling?
Edited 2 times.
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Author:
North Carolina Plumber (NC)
IF there is a vent downstream on the lateral, then yes an AAV will stop the gurgling. The tub drain is creating a vacuum and is pulling air thru the sink drain causing the noise you hear. The AAV will allow air to enter the system and the sink drain will not be affected.
If there is not a vent downstream the noise is likely being caused by a positive pressure , and the noise you hear is air being pushed up thru the trap, if that is the case then an AAV will not help at all.
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Author:
gmum (IL)
Since the tub is siphoning the sink trap (gurgle) does that mean the tub is not adaquetely vented thru the main stack?
And if I add the AAV to the trap arm of the sink, does that now mean the tub is completely vented thru it? And is that a bad thing?
And finally, if its positive pressure I assume that mean a sewer blockage... and in that case, positive pressure would also have slow draining or backup associated with it?
To test: whether its positive or negative pressure...and if the AAV would work, I could simply remove the trap from the sink for a moment and see if the gurgling still occurs? Is that correct thinking?
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Author:
KCRoto (MO)
The easiest way is to remove the trap and use a cigarette lighter next to the outlet. If the flame pulls toward the pipe opening, it is negative pressure and the AAV will help; if it pushes out, it is positive. Don't burn yourself or your property.
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Author:
gmum (IL)
the lighter test I think showed it sucking in (negative pressure).
So I put an AAV on the sink trap arm. It no longer gurgles! However, I can hear the AAV chirp a tiny bit instead.....I guess that goes with the territory of an AAV?
-- Does this confirm I had a negative pressure issue instead of positive?
-- When there is positive pressure, like when my town jets out the sewers, does that damage an AAV?
-- Was my setup as I describe above vented at all, with just the main stack venting that branch from 6-8' away?
-- Am I masking a clogged main stack vent?
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Author:
KCRoto (MO)
yes
no
probably not sufficiently
Unlikely. Corrosion buildup, or debris buildup in pipes can restrict airflow as well, and lines that are flat, or have a sag don't vent properly when the water level in the pipe rises during use, especially heavy use.
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Author:
gmum (IL)
thanks for answering my questions.
Last night I also notice a difference in the speed of draining / siphon of the tub drain... the siphonic action spins much faster around the strainer. That's why I was concerned that this is masking a bigger issue (ie main vent stack restriction or another restriction down stream?).
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