plumbing and vents

[joedirt63]

Hi guys, i have a question . Working on mom's kitcken sink. this not a mobile but i figure the plumbing should be same principle. Ok replumbed the kitchen sink drain pipe to a main drain (4 inch). old one was 1 1/2 metal pipe block solid for about 3 ft. ran 2 inch pipe from the main drain to the base of sink .then down to 1 1/2 pipe. now the old set up had just 1 roof vent in this section. the bath is on the oposite side of the house and has it's own drain and vent. apperently this kitchen was and add on. well any hooo. the drain goes down through the floor ,then straight to the main drain,aprox 12 feet with a 6 inch drop(slope). prob i have is the vent thing. Installed one just like i have on my m/h, when you fill the sink up and then pull the plug it goes down slow , as if it where blocked,but take the vent cap off and wooosh . feel pos pressure when i take the cap off. now this is a neg pressure cap, is there a pos pressure cap too? or is there a prob that i overlooked or created? I can run the water to wash dishes and stuff and it doesn't seen to back up thanks

[Greg]

I would think that if you have pressure when you remove the vent and not a vacuum there is a vent problem further down the line. Is she on a tank system or municipal. Any outside vents or ground vents?

Greg

[joedirt63]

hi greg she's on a municiple sewar. and the only vent i know of in that part of the drain was the one i bypassed with the rerouting. the house has 2 mains it seems and this one in question is closest to the street. don't see anything that looks like a vent out side on the grounds. my father-in -law was playing with this issue for years in this house, every time we did something it worked for a while then went right back to the same thing . figure if i did a straight run to the drain,without all the twist and turns, would eliminate clog points. plumbers got paid by linier ft of pipe used i guess. the original lay out made no sense.

[Greg]

You may want to check with the sewer dept. and see if there is supposed to be a vent anywhere between the house & the street. I have seen areas that use a ground vent, not sure if your's is the case or not.

Greg