What's the difference between an AAV and a cheap vent valve? I'm referring to the $3.00 1 1/2 inch vents with a one way rubber check valve that I believe are sold to vent kitchen sinks, and the more expensive $20.00 AAV Air Admittance Valves like a Studor.

They appear to do the same function. I tested both by sucking and blowing on them (new ones in the store) and they both seem to flow the same (when sucking). Both seem to open with very little effort.

The reason I'm asking - my copper kitchen sink drain (built in 1965) got plugged with 42 years of crud - too plugged to be snaked, so I cut the plugged section out and replaced it with PVC (with a Fernco to junction back to the copper). The original vent was a 15' long copper pipe that T'ed into the section going vertically down from the sink and joined a main vent (thru the roof) for a bathroom 15' away. I wasn't able to easily reattach this vent as I'd replaced the copper with PVC, so I put a cheap vent valve under the sink (T'ed in between the P trap and the vertical pipe going down into the crawl space.)

This cheap vent valve isn't doing the job - the sink drains slow. If I use a piece of wire and open the rubber check valve (pushing it open), it starts venting fine (you can hear the suction) and the sink immediately drains. It's as if there just isn't enough suction to open the rubber check valve flap, yet when I tested one in the store it didn't take very much effort at all to suck the valve open. I guess I have a hard time believing that buying the $20 Studor AAV will make any difference, but if you tell me that's what I need and it'll work I'll believe you. Just let me know why! I just don't want to spend $20 unnecessarily.

Also, would putting this vent as high as possible in the cabinet help? It's currently about 6" above the T where the P trap enters, so it's about at the same level as the bottom of the sink, maybe just a bit higher. I could get it a few inches higher, but it'll then hit the faucet plumbing. If I really need to, I could use some 90s and move it clear of obstructions and maybe get it near the cabinet top, which would be just under the countertop near the top of the sink. I'm thinking that in its current position, if the sink is draining really slow, since the sink water level is above the vent, maybe the water is backing up and filling the pipe completely all the way up to that vent check valve, so naturally it won't open.

Thanks for any advice you can give.

The cheaper aav is legal in mobile homes but has not been 'approved' by the code authority. It takes a lot of money for the approval process and they simply may not have submitted to it. As for your situation, I have seen the same situation with studor vents.

Thanks for responding Doug238. Since you've seen similar situations with the more expensive Studor vents, I assume replacing my cheaper vent valve with a Studor or similar AAV isn't the answer. What is the solution to my problem? What am I doing wrong?

As I mentioned, it seems I'm not creating enough suction to pull open the check valve, even though it appears to take very little suction to open the thing. If I unscrew the check valve and leave it loose, or totally leave it out, the sink drains quickly, but of course sewer gases can then escape. What am I doing wrong? Island sinks use AAVs all the time don't they?

You will either accept it or change the piping for the drain to at least 2" all the way to the 3"

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Originally Posted by Thrashercharged

Thanks for responding Doug238. Since you've seen similar situations with the more expensive Studor vents, I assume replacing my cheaper vent valve with a Studor or similar AAV isn't the answer. What is the solution to my problem? What am I doing wrong?

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Y'know, given that the drain works when you manually open the valve, it's possible that you simply have a defective "cheap vent valve".

Personally, I'd spend the $20.00 on the approved Studor Vent to see if it works any better than the forbidden knock-off.

Just my two pence.

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I assume replacing my cheaper vent valve with a Studor or similar AAV isn't the answer. What is the solution to my problem? What am I doing wrong?

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Both growler and Doug gave you the solution which is to replace your present AAV for one that works. OR you could complete the loop vent as Doug suggested. But I'd replace the AAV first. Just my two pence also.

Thanks for all the advice. I'll change out the cheap vent for a Studor as Growler and Speedball suggest.

I must not be seeing a post from Doug that others are seeing. Do you need special access to this forum to see all the responses? The only posts from Doug I can see are his first response that says "i have seen the same situation with studor vents." and his second response "you will either accept it or change the piping for the drain to at least 2" all the way to the 3" ". I don't see the post where he suggests replacing the cheap vent or to complete the loop vent that Speedball is referring to. What does completing the loop vent mean exactly?

This is Dougs post.

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Doug238
Ultra Member Join Date: Feb 2007
Location: atlanta metro area
Posts: 1,216
You will either accept it or change the piping for the drain to at least 2" all the way to the 3"

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Completing the loop would mean removing the AAV and running a pipe back to a dry vent. To do this the cabinet would have to come out and the return vent line run back under the floor. Major surgery that you don't want to get into. Regards, Tom

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Originally Posted by Thrashercharged

What's the difference between an AAV and a cheap vent valve? I'm referring to the $3.00 1 1/2 inch vents with a one way rubber check valve that I believe are sold to vent kitchen sinks, and the more expensive $20.00 AAV Air Admittance Valves like a Studor.

They appear to do the same function. I tested both by sucking and blowing on them (new ones in the store) and they both seem to flow the same (when sucking). Both seem to open with very little effort.

The reason I'm asking - my copper kitchen sink drain (built in 1965) got plugged with 42 years of crud - too plugged to be snaked, so I cut the plugged section out and replaced it with PVC (with a Fernco to junction back to the copper). The original vent was a 15' long copper pipe that T'ed into the section going vertically down from the sink and joined a main vent (thru the roof) for a bathroom 15' away. I wasn't able to easily reattach this vent as I'd replaced the copper with PVC, so I put a cheap vent valve under the sink (T'ed in between the P trap and the vertical pipe going down into the crawl space.)

This cheap vent valve isn't doing the job - the sink drains slow. If I use a piece of wire and open the rubber check valve (pushing it open), it starts venting fine (you can hear the suction) and the sink immediately drains. It's as if there just isn't enough suction to open the rubber check valve flap, yet when I tested one in the store it didn't take very much effort at all to suck the valve open. I guess I have a hard time believing that buying the $20 Studor AAV will make any difference, but if you tell me that's what I need and it'll work I'll believe you. Just let me know why! I just don't want to spend $20 unnecessarily.

Also, would putting this vent as high as possible in the cabinet help? It's currently about 6" above the T where the P trap enters, so it's about at the same level as the bottom of the sink, maybe just a bit higher. I could get it a few inches higher, but it'll then hit the faucet plumbing. If I really need to, I could use some 90s and move it clear of obstructions and maybe get it near the cabinet top, which would be just under the countertop near the top of the sink. I'm thinking that in its current position, if the sink is draining really slow, since the sink water level is above the vent, maybe the water is backing up and filling the pipe completely all the way up to that vent check valve, so naturally it won't open.

Thanks for any advice you can give.

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Just a quick follow-up to this thread, and hopefully if someone with the same issue is doing a search it'll help them too!

I replaced the cheap AAV with an expensive Studor, and it did no good, so that didn't help at all. Result - I re-plumbed the entire line from sink to 3" main sewer line - replaced the 1.5" line with a 2" line and gave it more slope (fall). When I cut into the 1.5" line, I found it totally plugged with just a dime size hole for water to go through. I'd just snaked it too - apparently a 1/4" snake doesn't really twist all that much inside the pipe, at best it just wallows a dime size hole out.

The original plumbers in 1965 put a funky bend with 2 90's in it (in 1.5" copper) in order to make a cleanout. This was the real problem, and why the blockage would eventually happen. If they'd just used 2 45's it might have been OK, but the 2 90's was just too much - it worked fine when new and clean, but give it a few months or years, and once those 90s got a bit clogged, it was catastrophic from that point on. Also with the 2 90s, it lifted the pipe about 4-6" higher than then level of the 3" main sewer line, giving me less slope (fall). So I capped that off, and went straight into my 3" main sewer with a 2" line, and gained some slope (fall) and lost the cleanout. I figure if it does get slow again - I really don't expect it to - I can take off the AAV under my sink and snake with a 1/2" snake.

Oh - and I did put my AAV at the highest point, just under the lip of my sink, so if it does get stopped up, the water level would have to be at the top of my sink to get close to shutting off the AAV.

Again, thanks to all the veteran plumbers who responded and helped me out!

Oh - one more thing to avoid confusion - I actually put in 2 AAVs - one in the original location straight off the main pipe going vertically down - this one is lower than the sink level - I kept it there so I had something I could easily unscrew to run a snake straight down. I put another off this main pipe (using a 45) that runs high to the sink lip level, the idea being if I do get a massive clog, it'll remain open while the other lower one (that I intend to snake through) may close off due to the water level.

Regarding my initial question about cheap and expensive AAVs - the owner of the local plumbing supply store (that all the pros seem to use) said for a single kitchen sink, the cheap AAV was fine - said this was a grey area in local code on whether it met code or not, but I'd need the Studor if I was venting more than just that sink. He said "I just make more money on the expensive one". He did say that the Studor had a superior check valve design though.

I'll add on more thing just to answer my initial questions in case someone is searching for this very topic. As to why my AAV wasn't opening and allowing air in (if I manually pushed the rubber check valve open the sink would then drain better), the plumbing supply store owner said my pipe was so clogged, and the slope so small (almost flat) that the water velocity just wasn't fast enough to create enough suction to pull open the AAV check valve (neither the cheap nor the expensive one).