Some time back, I asked a similar question, and got good, but not conclusive
opinions...partly due to a not having good wording of my question.
I looked up vacuum on Wikipedia, and got a huge amount of history and technical
information, more case histories of how fundamental religious beliefs can be
dangerous, and a useful set of numbers defining different vacuums, shown below:
I have seen 4CX-250Bs in military stocks, that were suspended in a plastic
shock mount, inside a one-time use,
sealed vacuum tin can. OD green, and about the size of 3 stacked tuna cans.
Pull tab top, that first breaks the vacuum, then
peels back along a scored groove, like a sardine can. Remove 4CX 250B from the
can, then from its molded plastic shock mount.
Presumably extends the shelf life of the Mil Spec 4CX 250B due to the vacuum
inside the can, slowing ingress of
air molecules past tube ceramic to metal seals.
My questions:
What level vacuum was likely drawn on the one time use, storage can? Low,
Medium or High?
1 Torr, I believe is 1 mm of mercury, which appears from the table below to be
not quite 3 orders of magnitude from atmospheric
If you could in a simple way, evacuate a cheap, re-sealable container to 1
Torr, and store a 3-500Z in it, you could reduce the differential
pressure across the pin to glass seals by almost 3 orders of magnitude.
Is 1 Torr simple to achieve with cheap shop compressor/vacuum pumps?
If you you could put 1 Torr of pressure in a simple container, how often would
you have to refresh the vacuum to keep close to the 1 Torr value?
Would 1 Torr outside pressure on a say, 3-500Z which I presume, has a very
"hard" vacuum,
dramatically slow the ingress of air into the tube over a long period of time?
If so, then someone could help frugal hams by designing a similar, but re
usable, home-evacuatable can that
could vacuum pack 3-500Zs and the like, extending their life during/after long
times of storage.
best, 73, de Pat AA6EG
pressure (Torr)
pressure (Pa)
Atmospheric pressure
760
101.3 kPa
Low vacuum
760 to 25
100 kPa to 3 kPa
Medium vacuum
25 to 1×10−3
3 kPa to 100 mPa
High vacuum
1×10−3 to 1×10−9
100 mPa to 100 nPa
Ultra high vacuum
1×10−9 to 1×10−12
100 nPa to 100 pPa
Extremely high vacuum
<1×10−12
<100 pPa
Outer Space
1×10−6 to <3×10−17
100 µPa to <3fPa
Perfect vacuum
0
0 Pa
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