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Thread: Existing PVC pipe a bit oval, too tight for new fitting... what to do?

  1. #1

    Default Existing PVC pipe a bit oval, too tight for new fitting... what to do?

    I am making changes to the piping layout of my existing irrigation system. I have come across some existing pieces of 1/2" CL-200 pipe that is not dry fitting into new fittings due to the OD being too large, particularly in one diameter direction. I have tried solvent gluing a fitting on one of the pipes only to have it stop 1/4 of the way into the socket, causing me to have to cut it off and start over. The specs for 1/2" PVC OD is .084". I am getting up to .086 in one direction even though I am not getting a corresponding lower reading 90 degrees around the pipe. It is as if the pipe is swollen a bit in one plane. Is that likely? It is the thin-walled CL-200 pipe and has been in service for eight years.

    Are there any standard practices for this situation. Do I just sand the pipe to get it down the the correct diameter, or what?

  2. #2
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    First off, quit trying to dry fit PVC. Even brand new PVC is not intended to be dry fit. The so called, PVC "glue" or "cement" is neither. It is a solvent that melts the top layer of PVC in both the fitting and the pipe. When the parts are slipped together, the melted surfaces fuse together and create a solvent weld. Second, you will have to cut out the flattened pieces until you get to round pipe. The thin wall is the pits, I have a system I installed in 1984 and that's what was used then. Fortunately, I buried it quite deep so I haven't had too many problems with breakage. I don't think you need to use a micrometer to test for roundness, eyeballing should do it.

  3. #3


    Gary, thanks for the reply.

    It is interesting that you do not dry fit first. Perhaps by "dry fit" you thought I was attempting to fully seat the pipe in the socket to check the fit it will have after assembly. I know you can't do that because it is a tapered interference fit.

    I have always followed the solvent manufacturer's recommendation to test the dry fit first to be sure the pipe goes about 1/3 of the way into the socket before applying the primer to see if there are any irregularities (burrs, ridges, etc.) that may impede getting the pipe fully into the socket after you apply the solvent. In fact, if I had checked the fit on the piece of pipe in question (in a hurry, you know) I would have found it didn't fit and would have saved the trouble of cutting out the fitting and starting all over. Yeah, I know it is solvent welding even though the can says "cement". Even with the solvent softening the pipe and socket, the pipe only made it 1/4 of the way into the socket.

    What I found is that the pipe had become deformed by the pressure of the PVC cutter, despite a new sharp blade. The pipe looked perfectly round to the eye, but just wouldn't go into the socket. When I checked with a micrometer, I found the deformation. It actually was a square shape, not an oval. That is why the reading 90 degrees around the pipe wasn't lower. What I did was use a hacksaw to recut the pipe. Even then, the pipe became a bit deformed (damn thin walled stuff). I squeezed the pipe a bit with pliers (using cardboard for protection) to form it back into shape. I then used a sanding sponge to smooth the end and mating surface of the pipe and it finally fit into the socket.
    Last edited by vivona; 10-24-2010 at 07:54 PM.

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