Two things helped a lot: Big pumps and an LN2 cold trap. The LN2 trap (as long as it is kept filled) will condense most everything except a few "permanent" gases. It also stops the backflow of pump oil. However, if something goes wrong, you would not believe the mess.
A technician that worked for me years ago told of a vacuum chamber that was used to test some Apollo instruments, maybe 6' long and 5' diameter with a pair of 18" - 24" oil diff pumps. One night the AC power went off and the emergency sequence failed. The diff pump oil was sucked back into the system. It took them weeks to take the whole thing appart, clean everything (think 55 gallon drums of Trichlor) and get it back together. No thanks, -John ========== > > On Sep 2, 2010, at 10:28 AM, Corby Dawson wrote: >> This EFOS maser typically runs with the two vacuum pressures below 1.5 X >> 10-6 Torr. (as measured via the ion pump current) >> >> Maximum should not exceed about 3.6 X 10-6 Torr for either pump. >> >> The internal vacuum will drop to about 1 X10-7 Torr if the Hydrogen to >> the disassociator is turned off. > > > Back in college, I took a semiconductor device physics course which > included a lab where we made simple ICs (the most complex devices were SR > latches). We had a vapor deposition system for plating on gold or > aluminum, which pumped the chamber down below 10E-12 Torr as I recall, > within ten minutes or so after a clueless freshman opened the beast up and > tossed in a bit of aluminum or gold wire and a few chunks of silicon with > their grubby hands (ok, we used tweezers, but still...). The whole unit > was about as big as a refrigerator or two. It used a rotary-vane roughing > pump and an oil diffusion pump with a liquid nitrogen trap. This was about > 25 years ago. > > Reading here about the troubles of pulling a very good vacuum, I'm now > wondering what sorts of painful engineering went into making the machine > turn-key and freshman-proof? It's entirely possible that I've > mis-remembered the pressure level, but that's the exponent that stuck in > my mind for whatever reason. > > -- > Mark J. Blair, NF6X <n...@nf6x.net> > Web page: http://www.nf6x.net/ > GnuPG public key available from my web page. > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.