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Smawgunner
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# Posted: 29 Jun 2015 08:58pm
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This may not apply to cabins but since most of us on here are fairly handy, maybe some of you have some experience with these valves. Basically I'm remodeling our kitchen and have an island with a sink (main kitchen sink) that cannot be vented. I have one waste stack in the house that is vented through the roof. I also have a bathroom upstairs that already has one of these valves. The system seems to be working just fine with no slow drains etc. Our house is pretty small. Would you be afraid to put two of these in a small house system?
Thanks!!
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Don_P
Member
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# Posted: 29 Jun 2015 09:58pm
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No, just bear in mind it is a mechanical valve, subject to failure. Look there first if your nose knows something is amiss.
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bldginsp
Member
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# Posted: 30 Jun 2015 12:12am
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Air admittance valves, or 'Studor vents' as the brand name goes, only do one half the function of a plumbing vent. All they can do is let air in, and they prevent it going out.
When you flush the toilet or pull the plug on the sink or tub, a vent does two jobs. First, as the initial rush of water enters the waste lines, the vent gives the displaced air somewhere to go. If that air has no where to go it gurgles up past the trap (sometimes) and you get sewer gas in the house, which is unhealthy.
Then, as the rush of water from the sink continues down the pipe, the vent does the second job, which is to prevent the trap from being siphoned, leaving it dry, which again lets gas in the house. The vent lets air in the pipe as the water flows away to take up the displaced area.
Admittance valves do the second job, not the first. Probably the second job is the more important of the two, to leave the trap with water in it. In most circumstances the first job of giving displaced air a place to go as water comes in is less necessary because if the water is not flowing quickly there is enough room in the pipe for displaced air to move to a different vent. But siphoning can occur with relatively little water flowing because it creates a bit of a vacuum in the pipe, enough to siphon the trap. At least that's how they explain it to me.
Most building departments don't accept them for this reason. You can instal a foot vent in a kitchen island which is a bit tricky but solves the problem, then you are not relying on a little plastic flapper valve in the Studor vent to keep sewer gas out of your house.
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bldginsp
Member
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# Posted: 30 Jun 2015 12:26am
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But to address your basic question, "would you be afraid to instal two of these in your house" I think it's important to realize that with Studors your venting for the fixture with the Studor is relying on the other vents in the house to discharge displaced air when the water first enters the pipe. Point is that if you are relying on your other vents, but most of those are Studors, you have blocked off a lot of the capacity of the venting system as a whole to discharge air. In older houses they installed a central 3" vent stack that most vents were attached to, which lets a lot of air move easily. If your other venting is limited I'd reconsider. But I would never use a Studor vent anyway, just cause it's a compromise, and I don't like compromising on basic health functioning of plumbing.
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