Where is the weir?

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  #1  
Old 08-01-07, 06:11 PM
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Where is the weir?

This is a pretty novice question. . . but can any of you tell me where the weir of a trap is?

this link -> http://www.plumbinglessons.com/sup/trap.htm seems to imply that it is the lowest part of the trap, where the seal is created.

but this website -> http://www.ilga.gov/commission/jcar/admincode/077/07700890ZZ9996kmR.html
makes me think it is at the end of the trap where the drainage "spills over."

Which is it, a or b? (Or "C" - none of the above)

I am trying to make sure my vent starts above the weir, but i dont know what i am suppossed to be checking it against.

Thanks

-Ben
 
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Old 08-01-07, 06:23 PM
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here is a non-plumbers take on your q.

the weir is the portion that makes the seal. In the one that you state places the weir at the lowest point is your misunderstanding. What is states is the water in the one drawing is below where the seal would be created, which is the weir. That, to me, says the weir is higher than the water in the drawing.

The upper portion of the "U" shape section of the pipe, from what I can understand, is the weir. That is the portion that actually causes the seal when filled with water.
 
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Old 08-01-07, 06:33 PM
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ok. then i should make sure my vent starts above the top of the U, right?
 
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Old 08-02-07, 07:06 AM
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With the way plumbing is done in "p-trap" arrangements (typical under kitchen ands bathroom sinks), - the horizontal tube part of the p-trap goes directly into the "T" fitting of the combination drain (down)/vent (up) pipe.

So in a nutshell. the center of the entrance of the vent pipe is in line with the center of the horizontal member of the trap.
 
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Old 08-02-07, 05:31 PM
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http://www.ilga.gov/commission/jcar/admincode/077/07700890ZZ9996kmR.html shows the proper way. The crown weir is were the sewage flows out of the trap seal into the drain.

Although the pic in the above mentioned link doesn't show it, this also applies to any trap, even a toilet.
 
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Old 08-06-07, 06:10 AM
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that picture helps for a sink/shower weir. but now i am a little confused about the toilet weir.

as i understand it, a toilet's trap is built into the toilet fixture itself and the drainage pipe comes straight down then over horizontally to join the stack, making the beginning of vent pipe significantly lower then the trap. this picture illustrates what i am thinking:

www.usinspect.com/plumbing/Images/28_4g.gif

Where am i thinking wrong about this?
 
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Old 08-06-07, 06:37 AM
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What are you thinking wrong about?

In most new construction plumbing of sinks they try to 'dry vent' the drain and are able to do so according to the other poster's submited weir diagram.

With toilets, it would be impractical to have the trap come out exposed behind the back of the toilet-through the wall. So technically we may be dealing with a section of waste/vent pipe 1 or 1 1/2 feet of 'wet venting' of the toilet, where the size of the pipe is so large that there would never be any risk of loading up that section of pipe, solid with water, to create an unwanted syphon out of the toilet bowl, all by itself. And the drop through the floor probably helps assist the syphon flush action of the toilet.
 
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Old 08-06-07, 07:07 AM
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ok that clarifies it. I think i was being legalistic in thinking that the vent HAD to begin above the trap. But I understand your explanation. thanks!
 
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