[TheForge] teflon, ice rink, leaks, etc.

[Bruce .]

Paul has it correct here.  And if you think loose teflon shards are a
problem in home plumbing, just try letting them loose in laboratory
instrumentation!

A clarification:  While teflon is probably incompressible, it does
"cold-flow".   If you take a piece of teflon and apply a strong force to
it, it will flow away from the pressure point until much of the pressure is
dissipated.  I've seen this many times, and it is the reason for the
existence of "filled teflon" -- teflon with fiberglass or other supporting
materials cast into it. These supported teflons better resist cold-flow,
but generally don't eliminate it completely.

The result is that if you use a slight excess of teflon tape on pipe
threads (one of the few places it should be used), the teflon will migrate
into the spiral channel implicit in the design of pipe threads.  This is
exactly what you want to happen, and means that teflon tape is likely to
perform better in these applications than semi-liquid pipe dope.  The the
operable term here is "slight excess".  Cram too much of anything into a
pipe joint and you're asking for trouble.  Pipe dope, however, will mainly
just make a mess.  I've never seen teflon tape cause a fitting to fail, but
I've never used it like that.

On Wed, Nov 21, 2012 at 9:26 AM, Paul Sperbeck <forge at wi.rr.com> wrote:

> Let me say that this comes form a plumber with 42 years experience... the
> lay public has no idea how to use teflon tape correctly. Most of the time I
> see 4 layers of tape with layers extending over the end of the male thread.
> When you screw this in you cut off the overhanging ends which then
> distribute themselves in all the wrong spots in your piping system. Too
> much tape, which is nearly incompressible, can also cause the fitting to
> stretch and fail.
>
> The tape you see on tank valves and professionally assembled fittings does
> not extend over the end of the pipe of fitting. We usually start back about
> 1/2 to 1 thread from the end, only apply one  to 1-1/2 layers of tape and
> use the correct tape for the application.
>
> Correctly installed, the amount of teflon tape exposed to the gas flow is
> on the order of 0.00004 square inches. Adiabatic compression which can
> result in autogenous ignition of the  teflon is extremely unlikely due to
> the quenching effect of the surrounding metal and the cooling which takes
> place as the gas travels along the spiral path of the thread. One can
> cannot say 'never' but I I think that I would in this case...
>
> Teflon correctly used is not meant to repair bad threads or loose fitting
> nuts and ferrules. I don't much care what you do on water systems, but high
> pressure gases are no joke.
>
> For another high pressure gas application see:
> http://www.quackenbushairguns.**com/index.htm<http://www.quackenbushairguns.com/index.htm>
> more than one way to get hurt...
>
> paul
> WB9HCO
> --
>
-- 
Bruce
NJ