[R-390] Filters (purge gas, foam replacement, paper/tape liner)

[Tisha Hayes]

What I have been using for a purge gas is a mixture of argon, carbon
dioxide and nitrogen. You can buy cans of the stuff on Amazon, it is called
"Oenohilia Private Preserve Wine Preserve". It is about $7 US a can and
comes with a spray nozzle.

For a while I was using something known as "zero air" that is used to
calibrate MSHA gas detectors as it had no moisture in it. My source dried
up (I no longer work for a company where gas detector calibration was one
of the catch-all duties I had picked up). The wine preservative gas does
that even better as the argon and carbon dioxide are heavy inert gases. For
PTO's I do a couple of shots down inside of the plug before sealing them
off. For a filter, if the seal is open then a shot or two ought to pretty
much outgas most of the oxygen.

Thinking about the foamy thing last night and I contemplated using 1/4"
silicon tubing, cut in a length to make a slightly snug fit around the
filter body and then super-gluing the ends together to make what looks like
a hollow "O ring". Given the size of the filter and the size of the bore
the hollow silicon O ring would hold the filter perfectly centered in the
filter body with a snug fit but not with crushing force. I have some high
temperature silicon tubing that is good up to 300C.

In lieu of the paper liner I thought about kapton tape on the inside of the
bore. You could make a reverse roll of tape (sticky side out) on the end of
a philips screwdriver and unwind it inside of the tube. I have some 30 mm
wide stuff that I could try out. It should only take two pieces (one from
either end) to fill most of the bore (except for the ends where the caps
need to solder back on and maybe a small gap in the middle where there is
nothing except for the resonator disks that should be nowhere near the
sidewalls anyway).

-- 
Ms. Tisha Hayes/ AA4HA


*"neque est alter hujus universi locus quam anima"*
*('For there is for this universe no other place than the soul or mind')*
*-Arthur Schopenhauer*