ABS/Polypropylene plumbing question


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Old 01-12-05, 05:35 AM
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ABS/Polypropylene plumbing question

Good day, everyone!

I'm installing a dishwasher and have a question about the existing drainage under the sink.

The current drain pipes are ABS for a double-bowl sink. I've attached a picture below to show the setup. My question is basically, what is this attachment rising off the exiting drain pipe in the center of the picture? It looks like it could be an air gap. Is this supposed to be attached AFTER the trap? The trap is just to the right of the picture attached to the pipe with the suspicious-looking power cord draped over it.

I'm planning on either replacing all the ABS and putting in polypropylene OR just splicing into the pipe right below the air gap. I'll have to use polypropylene because a dishwasher tee is nowhere to be found when it comes to ABS. Another question I have concerning this is, if I replace the ABS with polypropylene, what do I do about the air gap? Is it necessary in this installation? Would it be best just to splice into the pipe right underneath the air gap with a polypropylene pipe that has a dishwasher tee? If I do splice into the pipe, can I have the dishwasher drainage connection AFTER a trap? Would this allow sewer gas into the house?



Any help would be greatly appreciated!
 
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Old 01-12-05, 05:53 AM
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The "attachment" is an Air Admittance valve. They let air in to facilitate drainage and are used (where allowed by code) when there is no vent line. You cannot put the dishwasher drainline after the trap due to the sewer gas coming in. Have you thought about replacing with PVC? That way there are always the fittings you may need, including the dishwasher tee. Good luck.
 
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Old 01-12-05, 07:17 AM
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Thanks for your help! I said above that I was going to try the polypropylene instead of the ABS if I couldn't splice the waste tee for the dishwasher in after the trap.

Since I'll have to changeover to a different material, how do I handle this air admittance valve? Do they make a polypropylene alternative?

[As a side note: how does the air admittance valve work? I'm assuming it's one-way to only allow air to be sucked in but to not let sewer gas in.]
 
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Old 01-12-05, 07:36 AM
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I included a link to a maker of air admittance valves so you could see how they work. Not sure what all materials they make them out of but probably any type that there is pipe types.

http://www.studor.com/index.htm
 
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Old 01-12-05, 02:08 PM
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This is great info! Thanks! I'm wondering if Lowe's sells them. I may just try to use this ABS AAV since I already have an ABS to polypropylene adapter.

Again, thanks for the help! I'll probably keep these AAV's in mind for any future plumbing projects. That's handy!
 
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Old 01-12-05, 02:15 PM
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I found something at Lowes.com called a "mechanical plumbing vent." It looks exactly like what's on my plumbing. I'm assuming it's the same thing as an air admittance valve. A rose by any other name....
 
 

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