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Amber 04-14-2008 04:43 PM

Moving kitchen sink - how far can vent lines travel?
I need to move my kitchen sink (and dishwasher and disposal) to an outside wall. I determined I have enough room to provide a 1/4" downward slope per foot the drain travels. The supply seems simple enough. I understand I need to insulate pipes on the outside wall.

I do not know what is required in moving the vent lines. Can they go horizontal 11 feet including around a corner? Even if I put a new roof vent above the new location, I can't vent straight up because it will be in front of a window. One suggestion I got was to use the mushroomy thing used in trailers but I fear that might stink (and is illegal?)

Thanks for your help.

glennjanie 04-14-2008 09:49 PM

Hello Amber:
Plumbing codes are different in each state but your 11' vent will be much b3etter than none at all. The only problem is, it sounds like you will be running this vent inside the cabinets, whereas a vent is not supposed to go horizontal until it is 6" above the flood rim of the highest fixture on that floor; and the vent should run in an uphill grade to provide for drainage of condensation in the pipe.
It may be possible to run the drain 3' or so to the side of the sink, then run the vent up through the roof and the drain down through the floor at that point. Of course, each penetration of the roof is another potential leak, so the vent could be run up to above the top plate then across to the main vent. The vent can be run up to 25' in this manner. This could be much more comfortable to run than draining through the cabinets.

majakdragon 04-15-2008 09:28 AM

That "mushroomy" thing is called an Air Admittance Valve and they are normally used for island sinks in all types of homes (not just trailers). They are a one-way valve that allows air in to facilitate drainage. Most, but not all, areas allow them. You would need to check Local Codes. Studor is one brand I am aware of and have used in many new construction homes.

glennjanie 04-15-2008 11:34 PM

My experience with air admittance valves: they use a small spring to close the valve when there is a positive pressure in the drain-waste-vent system, and the spring allows the valve to open when there is a negative pressure or vacum in the system. In the process of draining the kitchen sink you may have pressure and vacum at different times; sometimes alternating up to three times. Sewer systems have alternate acidic and caustic liquids and sometimes gasses which will rust and dissolve the spring, disabling the mechanical regulation of the valve.
The code in my state disallows any mechanical traps or vents.

triple D 04-17-2008 10:46 PM

Just wondering....
Can you send us a picture of current plumbing location, and future location? Might help in offering more precise advice, we're always here to help, or at least make ya lol. Good luck....

mstplumber 05-03-2008 01:28 PM

Actually, a Studor brand Air Admittance Valve uses no springs. It has an ingeniously designed seal that opens under negative pressure in the pipe to allow air into the system and closes under positive pressure. If your local code allows it you can feel comfortable using one, I have installed literally thousands with very few failures. If they do fail you will smell a sewer gas odor and can just replace the AAV (Air Admittance Valve). One thing to be careful of is to use Teflon tape on the threads instead of pipe dope. If you get any pipe dope inside it could interfere with the seal. The same goes for PVC glue.

I am a little concerned that you are going to run your supply lines in an outside wall. Insulation provides no heat and may not protect your pipes if it gets really cold. A better solution might be to bring the supplies up from the bottom of the cabinet if this is possible.

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