Under Sink Vent

jatoxico

Minister of Fire
Aug 8, 2011
4,334
Long Island NY
Fella's I have a peninsula sink w/ an under sink vent (no vent to the roof). Sink is draining slow but drains fine with vent out.
Couple quick questions;

If I blow into the vent it doesn't seem very restricted, do they go bad?

It's a very tight fit so my options may be limited but are there any out there that are better, maybe even lifetime replacement?

There's no size on it (Studor Redi-Vent). How do you measure the size? The OD at the threaded end is 1 7/8"
 

semipro

Minister of Fire
Jan 12, 2009
3,958
SW Virginia
If I blow into the vent it doesn't seem very restricted, do they go bad?
Hmm. If you blow into the threaded end of the vent it's supposed to restrict airflow completely. Air is only supposed to flow into the vent from above.
Sucking on the vent would a better test.
Not too long ago I looked to see if I could find a better quality air admittance vent than the one you have and I don't recall being successful.
 

jatoxico

Minister of Fire
Aug 8, 2011
4,334
Long Island NY
This is it. I was blowing into the little grids on top. I wouldn't put the threaded end anywhere near my mouth and I got the COVID vaccine!

It let air in without much difficulty but I have no reference. How is PVC pipe measured ID or OD?

1610147543459.png
 

rwhite

Minister of Fire
Nov 8, 2011
1,798
North Central Idaho
Should be measured at the inside diameter of the female end that the vent screws into. So deducting 1/8" each side for threads you are at 1.5" fitting
 
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rwhite

Minister of Fire
Nov 8, 2011
1,798
North Central Idaho
I suppose the valve could get calcified and stuck but normally when they go bad you can smell sewer gas. I've never seen one go bad as you describe. Not that it cant happen though.
 

semipro

Minister of Fire
Jan 12, 2009
3,958
SW Virginia
I wonder if your drain is partially clogged and removing the vent is enabling it to work better.
 

jatoxico

Minister of Fire
Aug 8, 2011
4,334
Long Island NY
I wonder if your drain is partially clogged and removing the vent is enabling it to work better.
Its possible. The line has a slight negative pitch 10-12' down the line just before it goes vertical and into the main.
 

Highbeam

Minister of Fire
Dec 28, 2006
18,563
Mt. Rainier Foothills, WA
Bring the old one when you get the new one. It’s most likely 1.5” with a slight chance it could be 2” but very small chance. You can buy them at Home Depot. Not super expensive.
 
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jatoxico

Minister of Fire
Aug 8, 2011
4,334
Long Island NY
I think you guys are right its a 1.5". I'll replace it, it's cheap enough but not too confident it will do much. More likely I need to put a another cleanout on the line so I don't have to pull the trap apart just to run a snake.
 

semipro

Minister of Fire
Jan 12, 2009
3,958
SW Virginia
You can also do this sort of thing for venting though I'd try to stay with the air admittance valve if you can.
1610159824637.png


1610159767581.png
 

zrock

Minister of Fire
Dec 2, 2017
1,030
bc
those vents have a flapper and seal in them so blowing in the top will do nothing. They are designed to keep sewer gasses in the pipe and not escaping. Never seen one go bad before and i would bet you are getting a blockage farther down the line. Probably time to snake it out. I just had to do mine and the blockage was 25 feet down the line where all the grease had built up..
 

jatoxico

Minister of Fire
Aug 8, 2011
4,334
Long Island NY
those vents have a flapper and seal in them so blowing in the top will do nothing. They are designed to keep sewer gasses in the pipe and not escaping.
No sewer gas smell that I noticed so it is sealing closed. My thinking was that besides sealing to keep gases in they also have to let adequate amounts of air in so blowing through the vent would let me know if that was working as it should. As I said it doesn't seem too restricted or difficult to blow into it so I think you may be right about the line itself being clogged.

What I didn't say was we had a plumber out who said it was probably the vent and that they need to be replaced after a couple years which is why I asked about that. Nice guy but he didn't seem too swift. He said there was no way he could get the vent out (it is a tight squeeze). I had it out 5 minutes after he left.
 
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John Galt

Member
Oct 22, 2019
96
W Montana
Those only last 7-10 years. Since it drains slow with the valve normally without the valve, it should all work once a new valve is installed. The main purpose of the valve is to let air enter the drain line to avoid a vacuum, allowing the water to drain smoothly and keeping the P-trap from getting syphoned dry. It has a check valve to keep sewer gas from coming in the house. Plumbers like them because they are quick to install vs the diagram pictured above which used to be the only way to vent an island sink.
 

Highbeam

Minister of Fire
Dec 28, 2006
18,563
Mt. Rainier Foothills, WA
Those only last 7-10 years. Since it drains slow with the valve normally without the valve, it should all work once a new valve is installed. The main purpose of the valve is to let air enter the drain line to avoid a vacuum, allowing the water to drain smoothly and keeping the P-trap from getting syphoned dry. It has a check valve to keep sewer gas from coming in the house. Plumbers like them because they are quick to install vs the diagram pictured above which used to be the only way to vent an island sink.
I wish they were more common. I hate roof penetrations!
 

John Galt

Member
Oct 22, 2019
96
W Montana
Agreed. I'm tying all of my vents together and running out a wall.
 

zrock

Minister of Fire
Dec 2, 2017
1,030
bc
No sewer gas smell that I noticed so it is sealing closed. My thinking was that besides sealing to keep gases in they also have to let adequate amounts of air in so blowing through the vent would let me know if that was working as it should. As I said it doesn't seem too restricted or difficult to blow into it so I think you may be right about the line itself being clogged.

What I didn't say was we had a plumber out who said it was probably the vent and that they need to be replaced after a couple years which is why I asked about that. Nice guy but he didn't seem too swift. He said there was no way he could get the vent out (it is a tight squeeze). I had it out 5 minutes after he left.
Some plumbers are totally useless... A few years back i worked at a modular park and one winter we got a $5000 water bill way higher that it ever was.. After a few days of searching i finally climbed under a tenants home and their main water line was snapped right off... and yet they tied to tell me they still had water..LOL... Had the tenant call the plumber as it was her side of plumbing that broke. When he came he proceeded to ask how i knew the line was broke as he could not see it (from standing 10 feet away from home).. he proceeded to be a real ass and ended up leaving without telling the tenant. He called the tenant and tried to say it was our job to fix it and sent her a bill and did not even go under the trailer.
 

jatoxico

Minister of Fire
Aug 8, 2011
4,334
Long Island NY
So I replaced the vent the other day and there is a small improvement but its not a night and day difference. I didn't tell the wife and she commented it seemed to be working better and it drains well enough but I need to add a clean out so I can run a snake w/o having to go under the cabinet and pull the trap.