Why do I need vents? (How about AAVs?)

talkingdog · Jun 20, 2007

Well, I should emphasize that I am confusing this thread by showing off all those new gadgets. This is the latest stuff, and I've never seen it used on the actual site.

Usually you see the standard 40, 50 and 75 mm gray PVC pipe, elbows, etc.

Now, as for the smell of sewer gases inside other people's house, I can't say I've noticed that. A friend of mine, who DIYed his whole house, and the plumbing, too, with a proper vent system, says that he can smell it, and it's just more factor in the overall poor indoor air quality.

talkingdog · Jun 20, 2007

You won't appreciate how high the standards are in the US until you see how the rest of the world lives.

Sponsor · 2022-01-29T12:20:58-0800

Geniescience · Jun 21, 2007

in a post above, metric pipe sizes are given; they are not oversized so you do not have that extra layer of protection,

in all those diagrams and pictures, we never saw YOUR layout. That will enable plumbers to answer your main question, as to where to vent. One real vent is cheap insurance. AAVs are even cheaper insurance, and they work best when the house has at least one real vent. In your new house the plumbing is to be all on the same floor.

if no-one in Japan has vents, and no-one in Japan has sewer gases (which can smell very foul!) in the house, then what is happening?

david

talkingdog · Jun 21, 2007

I'll post a floorplan, but I don't have proper plumbing plan yet. I'm not asking you all for a free design, though, just an evaluation of whether I can get away with going heavy on the AAVs, from a commonsensical POV.

Now, I did some more research on AAVs, and the "preventions of noxious odors" is listed as one of the benefits on the Japanese promo. Just because I can't smell it doesn't mean it isn't there.

Jadnashua · Jun 21, 2007

Whne water moves through a drain, it can create vacuum and pressure. The vent allows things to flow without disrupting the seals on other traps. An AAV is a one-way valve (assuming it is working right), it lets air in, but not out. Because air might need to move both ways, it can't be the only vent in the system.

talkingdog · Jun 21, 2007

Thanks, that's a very succinct and clear summary of the problem. Fortunately, in my design there is a pipe chase that goes all the way up to the ridgepole, so that would be a natural place to put the main vent, in the case of using AAVs elsewhere.

talkingdog · Jun 21, 2007

There's a good little photo essay on this page, which shows all the rough plumbing in a house, including a second floor WC, with funny looking silver insulation that I think is soundproofing. The white rounds outside are the traps, for sewer and rainwater.

At the bottom of the page is a Durco AAV installed under the kitchen sink to alleviate the noise
http://myhome-a.hp.infoseek.co.jp/kyuhaikan.html

GrumpyPlumber · Jun 21, 2007

Terry and "Talkingdog",
Now that I think of it..I know what that set-up is...it's VERY new...I remember an experimental commercial building in my state going up a few years ago....rumor was it was getting some new Japanese single pipe self vented plumbing.
I'd heard the horizantal drains were sized and shaped an unusual way to allow air to pass over the drainage...it was a strange nonconcentric shape.
Last night as I was looking at the diagrams it was nibbling at the back of my mind...thats what I was looking at.

"Talkingdog" strike all I said about venting with your system...what you have going in is state of the art (as long as it's what I think it is), currently seeking code approval in my state

talkingdog · Jun 22, 2007

I dunno, I've looked pretty carefully at the language they are using in promoting that equipment and I don't see them hyping it as a replacement for venting.

Here's what it says:

---
egg-shaped header section
--shape ensures air layer
--transport ability improved
--rupture prevention
--stoppage prevention

high placement of 50 mm inlets
--prevents backflow

---

I think that air layer in the header probably helps with the vacuum/syphon issue you mentioned. But the language they are using is not the same language used in talking about venting, so I would infer that it's probably overly optimistic to think this will substitute for vents.

I spent a lot of time thinking about this today and concluded that the reason we don't have a vent requirement is probably building code politics, rather than a sound technical reason. Can't repeal the laws of physics.

Geniescience · Jun 22, 2007

talkingdog said:
egg-shaped header section
--shape ensures air layer
--transport ability improved
.... helps with the vacuum/syphon ...

no, it IS a vent internal to the pipe, the egg-shaped cross-section IS an advantage both for transport of water + solids, and to allow air to move backwards (against the flow) to replace the volume left when water moves out. If we don't call it a vent, then we can call it a form of venting defined in the true sense of allowing for water and air to replace each other as one moves in one direction and the other in the other direction. With round pipes, oversizing them is not good, since it means that the drain water gets slowed down a lot by the friction against a flatter and flatter bottom; solids get droppped sooner and never get scoured away. So a narrow egg shape is highly intelligent design! You can't change the laws of physics. You work with them.

Even if each individual pipe is not shaped egg-y, the system seems t be designed to provide some (or sufficient) capacity to feed air backwards against the flow. In the diagrams, some key devices were egg shaped. That may be sufficient. Mere hard thinking won't resolve the question as to whether or not it is sufficient; more serious calculations and tests will deterine that. I would figure Japan has done that.

David

GrumpyPlumber · Jun 22, 2007

Talking....what genius just said exactly...that pipe is sized and shaped wqith an "air pocket" specifically for "self" venting...what you might do is look on the manufacturer site for referrals to existing structures...this stuff is VERY new....none of us will have much info on it...best to find the source - someone who has installed it..or a building owner/ maintanence dept that can tell you first hand how well it has held up.

talkingdog · Jun 22, 2007

Can I ask a related question?

Page back up to the first illustration. There are seven different catchment pits (what I referred to before as "traps") outside the house. Each fixture exits the house and has its own catchment.

Do you use the same system in US plumbing? Since the air freely exits and enters these pits, don't they also have some impact on the venting situation? I get the impression that this number of catchment pits is code required here, and it seems a little excessive. I can't find the same thing in the US plumbing literature I have here on my desk.

GrumpyPlumber · Jun 22, 2007

talkingdog said:
Do you use the same system in US plumbing?

NO, we vent through the roof to avoid the smell lingering.
Good catch on that question.

talkingdog · Jun 25, 2007

Further question on AAV and secondary venting, the following is from the Durgo manual:

>>An open vent pipe is needed to discharge the
air drawn in through the Air Admittance Valves
and to eliminate any possible positive pressure
in the DWV system. It is also necessary to vent
at least one vent to atmosphere in certain
jurisdictions to faciliate the entire DWV system.

>>In single-family housing developments, every
tenth house is usually equipped with an open vent
pipe located downstream. Since no cold air is flowing through the end of the sewer pipe, the risk of freezing is reduced in shallow runs of pipe.
<<

I'm not sure I understand the language used here. In the first line it says "an open vent pipe is needed," then in the next sentence it says "at least one vent to atmosphere," then finally it says "open vent downstream." Are all three of these the same thing, namely a vent riser that sticks up into the air. Or, for instance, does "open vent downstream" refer to a catchment pit such as I mentioned above?

talkingdog · Aug 27, 2007

I finally got my hands on Toto's system plumbing catalog, in which the above-mentioned egg-shaped header is listed. Whew! The prices are astounding.

Six port header lists for $450, and the flexible plastic elbow for exiting the waste lines from slab lists at over $200. Holy cow.

GrumpyPlumber · Aug 28, 2007

Welp...that might explain why it hasn't caught on in my state just yet...ouch.

Why do I need vents? (How about AAVs?)

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