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Author Topic: Moving kitchen sink - do I need an air admittance valve?  (Read 1656 times)

Phil Hyde

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Moving kitchen sink - do I need an air admittance valve?
« on: September 19, 2016, 11:00:21 PM »
We are remodeling our kitchen and discovered that the drain line has an air admittance valve.  Being in such close proximity to a vented drain pipe from the grey tank, is the air admittance valve necessary?  Eliminating it would make for a cleaner installation of the new cabinets.

NOTE: In the picture, the sink is on the left.  After the remodel, the sink will be about 18" closer to the vent stack.
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markhodges78

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #1 on: September 19, 2016, 11:22:25 PM »
Do you need it. .. No should you leave it... yes why because it will help your sink drain. The vent for the gray water is for odor, to aid in draining the tank, and to allow the air to escape the tank as the tank starts filing with liquid ..The tank vent is down line from the sink so it will do nothing to aid in the sink draining

MYRV2

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #2 on: September 25, 2016, 10:16:39 PM »
Do you need it. .. No should you leave it... yes why because it will help your sink drain. The vent for the gray water is for odor, to aid in draining the tank, and to allow the air to escape the tank as the tank starts filing with liquid ..The tank vent is down line from the sink so it will do nothing to aid in the sink draining

I thought it was so the draining water wouldn't syphion the p trap water???
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Gary RV_Wizard

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #3 on: September 26, 2016, 09:22:01 AM »
The plumbing code required it, so it's there. If there is a vent stack very close by, it's probably not strictly necessary, but plumbing history has shown that having the AAV avoids vent problems.

Quote
I thought it was so the draining water wouldn't syphion the p trap water???

It is. It does not help odors to escape - just the opposite. It's purpose is to let air IN, not to let vapors out. However, air must be able to enter when the tank is drained, so the AAV can help with that (but the tank vent stack is the primary source).
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markhodges78

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #4 on: September 26, 2016, 09:37:23 AM »
Yes that's why I said aid in the sink draining it will create a vacuum and suck the water out of the P-trap if the vacuum is strong enough. if the vacuum is not strong enough to pull the water then it will make you think the sink is stopped up  because it will drain slow...


The plumbing code required it, so it's there. If there is a vent stack very close by, it's probably not strictly necessary, but plumbing history has shown that having the AAV avoids vent problems.

It is. It does not help odors to escape - just the opposite. It's purpose is to let air IN, not to let vapors out. However, air must be able to enter when the tank is drained, so the AAV can help with that (but the tank vent stack is the primary source).

Phil Hyde

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #5 on: September 26, 2016, 09:58:46 AM »
Thanks for all of the replies and helpful information.  Despite our wanting to have a cleaner installation, we've decided to just leave the vent in.
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MYRV2

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #6 on: September 26, 2016, 10:04:52 AM »
Thanks for all of the replies and helpful information.  Despite our wanting to have a cleaner installation, we've decided to just leave the vent in.

great thread...it will be helpfull
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JoeFatz

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #7 on: October 05, 2016, 08:43:44 AM »
why don't you cap off the old location and put a pro vent under the sink in its new location, same result as what you have now, be sure if you do use a pro vent you install it above the height of the sink drain so it operates properly.
http://www.lowes.com/pd/Keeney-Mfg-Co-1-1-2-in-Plastic-Mechanical-Plumbing-Air-Admittance-Vent/1069119
http://www.homedepot.com/p/Sure-Vent-1-1-2-in-x-2-in-PVC-Air-Admittance-Valve-39016/100201861
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Phil Hyde

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #8 on: October 05, 2016, 10:29:22 PM »
why don't you cap off the old location and put a pro vent under the sink in its new location, same result as what you have now, be sure if you do use a pro vent you install it above the height of the sink drain so it operates properly.
http://www.lowes.com/pd/Keeney-Mfg-Co-1-1-2-in-Plastic-Mechanical-Plumbing-Air-Admittance-Vent/1069119
http://www.homedepot.com/p/Sure-Vent-1-1-2-in-x-2-in-PVC-Air-Admittance-Valve-39016/100201861

We're moving the sink over about 18" from it's current location.  Shortening the drain line. 

I appreciate the height comment - that makes sense.
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Lou Schneider

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #9 on: October 05, 2016, 11:43:44 PM »
Beware of sharing the tank's vent stack with a drain.   It works in a fixed dwelling because there's nothing but water going down the pipe.

But in an RV holding tank the vent has to be kept clear.  If it's blocked by a full pipe of water flowing into the tank, there's no place for the displaced air to get out and the drain will slow and stop flowing until the tank burps itself.

I ran into this with a Sierra 5th wheel that plumbed the tub drain into the grey tank vent stack.  If I had more than a few inches of water in the tub, it would drain a bit and then stop as if the tank was full.  Capping the tub drain for a couple of seconds to let the tank burp would let it drain again.

This was only a problem when the dump valve was closed.  When it was open, the tub drained as it should.

You may wind up with a similar problem if you empty a sink full of water into the grey tank vent line.
« Last Edit: October 05, 2016, 11:49:44 PM by Lou Schneider »

Rene T

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #10 on: October 06, 2016, 07:12:18 AM »
Beware of sharing the tank's vent stack with a drain.   It works in a fixed dwelling because there's nothing but water going down the pipe.

But in an RV holding tank the vent has to be kept clear.  If it's blocked by a full pipe of water flowing into the tank, there's no place for the displaced air to get out and the drain will slow and stop flowing until the tank burps itself.

I ran into this with a Sierra 5th wheel that plumbed the tub drain into the grey tank vent stack.  If I had more than a few inches of water in the tub, it would drain a bit and then stop as if the tank was full.  Capping the tub drain for a couple of seconds to let the tank burp would let it drain again.

This was only a problem when the dump valve was closed.  When it was open, the tub drained as it should.

You may wind up with a similar problem if you empty a sink full of water into the grey tank vent line.

Lou, if you look at his picture, the existing sink drain is plumbed to the vent pipe. If they never had issues before, I think they would be fine now as long as they do install a air admittance valve.
I guess a question to the OP would be how the sink drained before starting this project.
« Last Edit: October 06, 2016, 07:14:16 AM by Rene T »
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Phil Hyde

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #11 on: October 06, 2016, 09:35:40 AM »
I guess a question to the OP would be how the sink drained before starting this project.

Never had any issues.
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JimTheSoundman

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Re: Moving kitchen sink - do I need an air admittance valve?
« Reply #12 on: October 07, 2016, 10:33:30 AM »
You can certainly eliminate it, but without it your sink will make that "glub glub glub" noise when it drains.   It's similar to when you are getting bottled water out of a dispenser with one of those upside down 5 gallon plastic bottles.   That is the same as your sink without the air intake valve.

 

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