[NA]Home plumbing[NA]

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
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west Texas
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Dave Taylor
I have a small problem at home and it has led me to research AAVs (air admittance valves).
The kitchen sink was draining slowly so I had the line to the septic snaked. Plumber said he found nothing blocking the outflow so he looked around and took off the Oatey AAV and the sink drained normally. I ran to the hardware store and got a new one, put it on and the sink would not drain again. He started to unscrew the new AAV and as soon as he started, the sink drained ok.
In typical local repairmanship fashion, that was offered as the fix; leave the AAV partially unscrewed. I am unlikely to leave it at that.

So, my understanding of AAVs is that they don't really allow the sink to drain by letting air in, there is already a roomful of air on top of the sink water. What they are designed for is to prevent a slug of water from pulling the p-trap water out, which means sewer gas could enter the home (in the absence of a roof vent).

If so, why is this sink experiencing these symptoms??

Let's say it's the cheap Oatey 39012 valve and I want to upgrade to one that will open more readily. The Oatey spec sheet does not give its opening pressure. One called the Sioux Chief says it is sensitive to 0.01" (of what? water? mercury?). The only other one I can find is a Studor which says -0.010PSI.

No, I cannot do away with the AAV and install a 'normal vent' in this location.



*http://www.siouxchief.com/products/drainage/residential/turbovent?template=P3SpecSheets

http://www.studor.net/documents/0400-0004-092013 Mini-Vent.pdf
 
That is a weird issue for sure.....

The "Auto Vent" works exactly as you describe, prevents the P trap from being sucked dry......

Did the fixture drain fine in the past?
 
Yes and no, Ben. It has worked well 99% of the time for the last 17 years.
Occasionally I would have a buildup of grease/food particles which I was able to clean out by attaching a garden hose to a fitting under the sink, blasting downstream.
PS this is all 2" PVC, and 20' to the septic tank, with three 90° bends to get there.
 
Let'sgoflying! said:
Yes and no, Ben. It has worked well 99% of the time for the last 17 years.
Occasionally I would have a buildup of grease/food particles which I was able to clean out by attaching a garden hose to a fitting under the sink, blasting downstream.
PS this is all 2" PVC, and 20' to the septic tank, with three 90° bends to get there.
Click to expand...

You mean just this branch is 2" ??:dunno::dunno:..

You need at least 3" line from any toilet to carry solids to the septic tank. Surely there is a 3" if not a 4' line going into the tank??:dunno::confused:
 
denverpilot said:
Any chance you've plugged up a main drain air vent on the roof?
Click to expand...

Nate makes a good point... if the roof vent is restricted,then having to run the auto vent wide open and un restricted to vent the entire system will explain your issue..
 
I thought those air valves are used when a roof vent doesn't work - like on a kitchen sink mounted in an island. You can't have a vent pipe there because there is no way to hide it inside a wall. So the vent valve gets mounted under the counter. The vent allows air into the drain line so the water doesn't pull any suction from above. That's why the sink drains freely when you unscrewed the valve. But the second purpose of the valve is to prevent sewer gas from coming into the kitchen, on a normal vent it goes out above the roof.

I don't know the likelihood of two bad valves. Is there a dishwasher attached to that drain? Does is drain properly?
 
denverpilot said:
Any chance you've plugged up a main drain air vent on the roof?
Click to expand...

I would not suspect so as all the other drains in the house work 100%, I can run water down them all day long and it disappears quickly. What is a good way to test the roof air vent?

N801BH said:
You mean just this branch is 2" ??:dunno::dunno:..
You need at least 3" line from any toilet to carry solids to the septic tank. Surely there is a 3" if not a 4' line going into the tank??:dunno::confused:
Click to expand...

The line from this sink, disappearing into the slab is 2". There are waterclosets of course but they are rather remote from the kitchen sink and I am certain they are 4". There is an outdoor cleanout near the septic tank that is 4".

Matthew said:
I thought those air valves are used when a roof vent doesn't work - like on a kitchen sink mounted in an island. You can't have a vent pipe there because there is no way to hide it inside a wall. So the vent valve gets mounted under the counter. The vent allows air into the drain line so the water doesn't pull any suction from above. That's why the sink drains freely when you unscrewed the valve. But the second purpose of the valve is to prevent sewer gas from coming into the kitchen, on a normal vent it goes out above the roof.
I don't know the likelihood of two bad valves. Is there a dishwasher attached to that drain? Does is drain properly?
Click to expand...

That is the situation, there is not a reasonable way to run a hidden vent pipe through a wall so they used these AAVs. No dishwasher.

Thanks for putting your brain power to this, I am thinking of just trying a different brand AAV for now, maybe the spring is too strong on the Oatey.
 
Let'sgoflying! said:
What is a good way to test the roof air vent?
Click to expand...

Water hose...but other than an animal in the vent there isn't much chance of a plug there...unless one of your neighbors is mischievous...
 
Air admittance valves allow air to be pulled into the pipe, right? When you loosen yours and the water flows, is air actually escaping to allow the flow?

I suppose you can test by plugging the sink, filling with water, removing the AAV, pulling your hand over where the AAV goes, then pulling the drain plug for the sink. Is your hand being sucked on to the opening, or is pressure pushing past your hand? If the drain line from the sink is plugged, be prepared that water might come out from AAV port if it is not high enough (above level of water in the sink)

Also, for the heck of it, test the AAV when off by trying to suck and blow air thru it. It should only allow "suck". It is possible it was made wrong.
 
Garden hose in the roof vent....hmm.
I suppose due diligence would include someone monitoring the vents/sinks etc for overflow.
 
Let'sgoflying! said:
Garden hose in the roof vent....hmm.
I suppose due diligence would include someone monitoring the vents/sinks etc for overflow.
Click to expand...

yes, yes it would...but then those drains would already show as at least partially plugged...
 
Clark1961 said:
yes, yes it would...but then those drains would already show as at least partially plugged...
Click to expand...


Keep in mind.... Stuffing a hose into the roof vent will build up enough pressure to blow out (most) obstructions .. Every foot equals .43 PSI of head pressure...;);)
 
Let's say I decide to try a different aav.
And to be really sure it will open I will find the easiest opening one; the one that responds to the least P differential.
Should I choose one with a small DFU or a large DFU?
 
a1e197e7782b066ed2092bfd678fcce2.jpg


cc8fdc604f73c9b5b2fcada16851a5da.jpg
 
Oatey says the plumber installed the wrong AAV; the 39012 is a "Vent" for use in Mobile Homes Only. They offered the correct AAV pn. I have done so and the sink passes the drain test.
 
Let'sgoflying! said:
Oatey says the plumber installed the wrong AAV; the 39012 is a "Vent" for use in Mobile Homes Only. They offered the correct AAV pn. I have done so and the sink passes the drain test.
Click to expand...

That is a new one on me... I assume they have two different seat pressures???:dunno::dunno::confused:
 
Let'sgoflying! said:
Oatey says the plumber installed the wrong AAV; the 39012 is a "Vent" for use in Mobile Homes Only. They offered the correct AAV pn. I have done so and the sink passes the drain test.
Click to expand...

Good job Oatey.
 
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