When does a p-trap become an s-trap?
Hello,
I would like to fix two problems with my sink drain: 1) increase the drain speed, and 2) reduce noise. In the figure, I show the current configiration and it shows that I need to deal with a wall drain oulet that is quite low. I am wondering if changing to the proposed configuration (right part of the figure) would essentially create an s-trap. What I want to know is when a p-trap becomes an s-trap. If the drain pipe in the wall is vertical, then this means that at some distance from the p-trap, it is ok to have a vertical pipe, provided that it is vented. How far is this distance? Would my configuration work if the distance “D: is long enough? How long?
Thanks a lot.
Louis
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Replies
Is the pentagon-shaped thing in your diagram an air admittance valve?
There has to be a tee with the top of the tee going to a vent that is positioned so that there is a continuous layer of air between the trap and the tee; ie the arm of the tee can't be lower than the trap. The air admittance valve counts as a vent so this is legal if you have an AAV there. If you don't it's not.
If you don't maintain a layer of air you get issues with a vacuum being created if there is heavy flow.
Noise and low flow is probably best fixed with a bigger pipe. The pipe in the wall should be at least 1-1/2", often the trap is quite a bit smaller. Upgrading the trap to a larger diameter will probably help.
Yes, the pantagon-shaped object is an air admittance valve.
Thank you
OK. Do yourself a favor and match the size of the pipe in the wall.
Sounds good, my impression for the noise was that the drop was simply too long and when those little drops fall they land in the p-trap water from such a height that it is noisy. I was thus thinking of breaking this long drop. I will change the bathroom szed pipes (1 1/4) to a kitchen size (1 1/2).
Thanks
Louis
Try the butyl rubber tape I mentioned below. I’ve used that successfully in the past to quiet down noisy traps. It’s a high mass dampening material, somewhat similar to MLV sheet but moldable and sticky. It works well for this application.
Bill
AAV won't fix a slow draining sink since it can only "add" air to the drain not take it away. The reason it is slowly draining is either the air of water in the pipe downstream of the sink is not moving out of the way fast enough. With a well functioning drain, the air in front of the water draining down would move into the main stack which vents outside.
Slow drain is either clogged drain, clogged main stack/vent or sagging branch where this drain connects to the main stack.
The vertical part of the drain that is in the wall (not the part from the sink to the trap) should be at least 2”. You need a SANITARY TEE to transition the horizontal piece after the trap into the vertical run.
If your sink is draining slow, I’d check if the pipe is clogged with gunk (snake and/or drano), if it’s sloped 1/4” per foot in horizontal sections, and if it’s the right size pipe, in that order. Correct as necassary any problems you find.
If your main concern is noise, get some butyl rubber tape and wrap it around the trap and vertical pipe section in a spiral, molding it into a solid mass on the outside of the pipe. Butyl rubber tape will help a lot with noisy drain traps like this.
Bill