"fred" wrote in message ...
In article , Andy Hall
writes
On Wed, 3 Nov 2004 09:32:27 -0000, "Frank Stacey"
wrote:

For various reasons I find that a plumbing job on which I have embarked
involves using plastic (HEP) pipe for various awkward runs with copper
at
either end. Am I right to assume this can be done without restriction?

In some places I am using straight metal compression couplers between
copper
and plastic with an insert in the plastic pipe. In other places I have
plastic elbows with plastic on one branch and copper or chrome plated
copper
on the other. Are there any gotchas I should know about?

Check with the manufacturers, but generally push fit fittings for
plastic are OK with copper, but not with chrome plated copper where
they are apparently prone to slide off.

If you have to use chrome plated pipe, then it is better to transition
via a compression fitting and short length of plain copper tube to the
push fit fitting.

It's also important to follow the manufacturer's recommendation and
use a proper pipe cutter for the plastic and not a hack saw.



Excuse the paranoia, but once completed most of this stuff is going to
be
under the floor of a small bathroom and very inaccessible. I dread
having
to rip out my carefully installed fittings as water seeps through the
ceiling below!!

Frank [the tentative plumber]

I agree, with all of Andy's comments, but would add that my own rule is
never to use a fitting that is mechanically weaker than either/any of the
pipes to be joined, so if I am making plastic/plastic I use plastic,
copper/plastic I prefer to use compression and copper/copper I would never
use plastic. All to do with the risk of stressing/damaging the fitting
when
pipes inevitably get moved about during fitting and in the months/years
down the line.

Can you elaborate please. What you say doesn't makes sense as all joints:
plastic, copper, brass, etc, will move in use due to expansion. In joints
were there is excessive movement it is a concern that the O ring , although
keeping a seal will prematurely wear. Osma Gold has O rings with two
contact points. The O ring shape is a "W". This may prolong wear.

You can use a plastic joints on two copper pipes. I have seen these done
successfully on cold water. You can use copper or brass pushfit fittings on
two pieces of plastic pipe. Both are better than plastic/plastic as the
metal parts, pipe or fitting, is less prone to expanding and warping with
stress or heat.

Many plastic systems develop intermittent leaks, when the pipes and fitting
expand when they heat up.