Danny D:
No, the way I read that Lasco article, you should not be using EITHE
pipe dope OR teflon tape on plastic pipe threads.
You should be using a thread sealant meant for plastic threads ONLY.
The Lasco article really should come out and say that pipe dope is no
the same thing as thread sealant meant for plastic threads. It dance
around that point by saying that pipe dope hardens whereas threa
sealant for plastic pipe threads doesn't, thereby allowing it to b
pushed into leakage paths by the water pressure inside the pipe, thereb
blocking that leakage path. It also says that pipe dope and teflon mak
the threads slippery, thereby reducing friction and causin
overtightening, whereas a thread sealant meant for plastic threads won'
do that.
Putting the thread sealant on the male threads, then wrapping them wit
teflon tape is just as bad as using teflon tape only. The thickness o
the teflon tape you put on is going to increase the spreading force o
the female fitting making it more likely to split.
From my reading of that Lasco article, you should apply thread sealan
meant for plastic threads to your male plastic threads only, and the
screw on the female plastic thread. Tighten to finger tight and then n
more than two full turns after that.
If you've already used teflon tape on your threaded plastic joints, an
there's no splitting or leaking, I would just leave them as is. But, i
future, just use the red bottle that says it's meant for plastic an
nothing else.
I think everyone in here understands the principle of tapered threads
and that the idea behind teflon tape or pipe dope is that thes
materials get compressed between the make and female threads to seal th
joint against leakage. That Lasco article said that metal threads ca
gall at metal-to-metal contact points, and that the use of teflon tap
or pipe dope helps to prevent that. In the case of a smoot
plastic-to-plastic thread contact, there's no risk of galling so yo
don't need anything as thick as pipe dope or teflon tape to keep th
metals separated until the joint is fully tightened. With plasti
theads, all that's needed to seal the tightened joint is a fluid that'
viscous enough not to be pushed out of the joint by the water pressur
inside the pipe. I'm thinking that plastic fittings can be molded t
much better tolerances than iron pipe can be machined (because th
cutting tool wears down for one thing), so a fluid that's fairly thi
may still be viscous enough to not be pushed out of a small enoug
crevice in a threaded joint. Or, at least, at the lower water pressure
that plastic piping is suitable for. So, even if this thread sealan
you bought for plastic piping seems to be too thin compared to pip
dope, I would still use it by itself, which is what Lasko is telling yo
to do
--
nestork
