On Fri, 22 Jan 2010 02:45:13 -0600, Richard J Kinch
wrote:

My swimming pool pump quit, and the new one is just slightly longer, so to
connect it in the space available, I need what in steel pipe you would call
a threaded nipple, except in 2-inch PVC pipe. That is, instead of gluing a
PVC male adapter, which would add too much length. Swimming pool plumbing
has to be all plastic due to the chemistry of the water.

Now Home Depot threads steel pipe, with a nice powered pipe threader on the
plumbing pipe aisle, but when I asked them to thread some PVC they
practically called me a pervert. They said the only way to get threads on
a PVC pipe was to glue on a male adapter, and you can't thread PVC pipe.

However quite a few bits of the PVC pool plumbing appear to have been
threaded on-site. And interestingly, the classic Ridgid 12R pipe threader
has replacement dies specifically for PVC:

http://ridgid.com/Tools/Hand-Threader-Die-Heads/

So is threading PVC pipe an unnatural abomination like the top industry
experts at Home Depot, in their orange aprons, assert? Or just not often
worth the labor versus a glued fitting?

All the threaded PVC I've seen in process piping was schedule 80. I've
never witnessed PVC being threaded on site, but I'm not aware of any
reason it can't be as long as the pipe wall is heavy enough. I wonder
if the thread form is modified to account for the PVC's physical
properties? Threaded PVC joints are more prone to leaks than
metal-metal joints and must be made up carefully to avoid leaks.
Fittings with metal inserts are available to minimize the problem.

--
Ned Simmons