"Chip C" wrote in message
ups.com...
Have replaced some of the 1" cast-iron piping on the inlet and outlet
of a hot-water rad: new valves and new sections of vertical pipe that
come up through the floor, which in ignorance of the proper term I'll
call the riser nipples. One is 6.5" long, the other 7". They go into
the old elbows just below the subfloor. Those elbows and some of the
pipes that feed them are viewable - not really accessible - from below
through a hole in the basement ceiling.

So I need to screw the new valves onto the new nipples, and the new
nipples into the old elbows, tight enough not to leak, *BUT* the
valves have to line up to the rad (which isn't in yet). Alignment is
in conflict with tightness. This would seem to be a problem inherent
with threaded pipe, wherever a right-angle bend has to align?

I used white plumbing tape on the new nipples (a plumber I trust says
it's equivalent to pipe dope) and screwed it all together pretty
tight. Now that the system is pressurized, I believe there is a very,
very slow leak where one of the new riser nipples goes into the old
elbow. There is no dripping water but there is definite moisture on
the flange of the elbow around the new nipple.

But if I tighten it, the valve won't line up with the rad. I really
don't think I'm going to get a whole turn on the valve and nipple. I
could maybe get a quarter turn on the nipple, but then I'd have to
back the valve off by that much, which could make it leak. And I
really don't want to put a lot of force on any of it being unable to
effectively brace the elbow from below.

Am currently trying to think good thoughts all day in hopes that it'll
be dry by the time I get home.

What advice?

Use pipe dope rather than tape.

You can tighten pipe joints HARD. So don't be afraid to tighten it to where you
need it.

Bob