PVC dry fit tightness (interference)

[Tim Meneely]

Will a joint fit more loosely (deeper) with solvent than it does dry?

I'm using a Sioux Chief 884-PTM TKO closet flange (new, PVC, solvent weld) inside a 4-inch PVC pipe (Charlotte pipe, new). The flange readily slips about 1/2 inch into the pipe, but then it starts to stick. Using what I think is reasonable force I can dry fit it about 2 inches, which is still a half inch or so from bottoming out. To dry fit it the rest of the way would require a hammer or something.

I have three questions:

• Is the flange supposed to bottom out inside the pipe?
• Will the two fit more readily when I have primer and solvent on them? (I think they will, but counting on that is scary - what if they don't?)
• Should I do something to prep the two to make them slide together, for example use a little sandpaper? (This seems like a bad idea).

Note that I'll transition from new PVC to existing 3-inch copper using a Proflex coupling a few inches away from the 4x3" PVC elbow. While I trust the coupling and it's supported, I'm reluctant to bang on the PVC too hard.

I haven't glued anything yet so have all the freedom in the world.

Thank you,
Tim

 

[Jadnashua]

The socket in a pvc fitting is designed to be an interference fit. When you make the connection, the combination of the primer and the cement literally melt the surface of the pipe and fitting, and allow the pipe to be easily inserted to the bottom of the fitting. Then, when the solvent evaporates, it becomes solvent welded together. If you dry fit things, you will come up short. You need to account for the depth of the socket when figuring out the length of the pipe in between joints.

Note, because of the taper in the fitting, if you don't hold things in place until things start to solidify...the pipe will back out of the fitting some on its own. Also, when inserting the pipe, it works best to turn the pipe (or fitting) about a 1/4-turn to help spread and even out the now liquid plastic and ensure you get good coverage.

 

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[Tim Meneely]

Thanks, jadnashua. I have worked with PVC before, but only in 2-inch and smaller, and I don't remember having to adjust more than 1/8" or so. I suppose the interference is easier to overcome on the smaller size.

It still worries me that I just have to trust that it's gonna go the whole way into the fitting when there's solvent... A screw-up during closet flange installation would be hard to recover from (subfloor, tile, etc.)

Thanks,
Tim

 

[Terry]

They won't bottom out unless you've primed and glued them. You swerve them in with a smear. Measure as if they go in all the way; they will.

 

[Reach4]

It still worries me that I just have to trust that it's gonna go the whole way into the fitting when there's solvent... A screw-up during closet flange installation would be hard to recover from (subfloor, tile, etc.)

While the glue will work well, there are alternatives to glue. Read up on compression closet flanges. They would let you work slowly and not worry that you would do the glue wrong.

It is not my intention to talk you out of the glued flange. I was just pointing out an option.