Moving kitchen sink - do I need an air admittance valve?

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
Phil Hyde

Phil Hyde

Well-known member
Joined
Sep 5, 2011
Posts
654
Location
United States
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.
 

Attachments

  • 14391023_10208912199021059_8977648052493464387_n.jpg
    14391023_10208912199021059_8977648052493464387_n.jpg
    69.6 KB · Views: 64
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
 
markhodges78 said:
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
Click to expand...

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

I thought it was so the draining water wouldn't syphion the p trap water???
Click to expand...

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).
 
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...


Gary RV Roamer said:
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).
Click to expand...
 
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.
 
Phil Hyde said:
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.
Click to expand...

great thread...it will be helpfull
 
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
 
JoeFatz said:
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
Click to expand...

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.
 
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 Schneider said:
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.
Click to expand...

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.
 
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.
 
You must log in or register to reply here.

Latest posts

Members online

Total: 782 (members: 27, guests: 755)

Forum statistics

Threads
131,915
Posts
1,387,331
Members
137,666
Latest member
leblanc77
Back
Top Bottom