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Mr. Luddite

On 2/24/2014 7:52 PM, wrote:
On Mon, 24 Feb 2014 18:05:10 -0500, "Mr. Luddite"
wrote:

On 2/24/2014 5:06 PM, Wayne.B wrote:
On Mon, 24 Feb 2014 16:46:48 -0500, wrote:

I am starting to prefer the teflon paste.

===

Yes. I just finished a fairly complex plumbing job on the boat (new
distribution manifold for 4 zones of A/C cooling water). It has more
than 15 individual pipe joints and is driven by a 1 hp pool pump so
there is lots of pressure and lots of opportunity for leaks. Knock
on wood, everything worked fine with no leaks first time it was
powered up. I've always used teflon tape previously but I've had my
share of failed joints with that.

Teflon tape is tricky to use properly. It is often used in the high
vacuum industry for all the feedthrough fittings that need to seal
against a vacuum equivalent to 200 miles in space to atmospheric
pressure. Too little tape, it leaks. To much it leaks. One secret is
to wrap it in the direction of the thread, so when you are tightening
the connection fitting, the tape is not being stretched back against itself.

We couldn't use Teflon paste because it never completely cures and would
outgas into the vacuum.

The vacuum in outer space is 14.7 PSI if you maintained 1 BAR in the
vessel. . That is not really much. The galvanized piping in my shop
air system runs 150 PSI and it is tight.
I have done plenty of piping with teflon tape and this is really the
first time I had a problem. When I put the calipers on the fitting it
was about .040-.050" bigger than the threads on a female adapter at
the top of the stack.
I have an incident open at Hayward but they haven't come up with an
answer.
Using the pipe nipple does seem to be a good work around tho. I wish I
had started out that way and this would have been a 45 minute project,
not 4 days.

In a high vacuum chamber the delta P is not the issue. The issue is
prevention of any gas molecules leaking or permeating through seals into
the vacuum.

An air compressor system or a water tight fitting can still have a leak
that looks like the Grand Canyon in terms of an opening to a helium gas
molecule and will prevent the vacuum chamber from achieving it's
ultimate vacuum state. A good vacuum cleaner can draw a vacuum that is
14.6 PSI delta. It's getting to 14.66666666666669 that is difficult.