My first mechanical pump was a Sears Coldspot compressor. It could get a real small chamber to around 0.5 Torr. It logged about 1 hour before it seized up. My next pump was a venerable Cenco Megavac - late 50s vintage from a TV picture tube plant. Paid $50 for it and it turned out it had ingested glass and the innards were scored. My dorm room mate and I cleaned it out on a Fri evening in the bath tub with gasoline. (2 weekends confined to the dorm as punishment but at least the place didn't blow up.)
Badly scarred it could still get to a bit below 100 mTorr and it worked quite well with my first real diff pump, a 2" NRC from the same piece of picture tube making equipment that the Megavac came from (obviously a broken picture tube was the source of the glass).
My main pump now is a Welch 1402 ($35 plus $20 for a new shaft seal). I also have 4 Robinair pumps in two sizes, a sweet little Kinney for freeze drying, an old Cenco Hyvac that needs restoring, and something else I've never heard of, a Nelson. I still have the Megavac.
Belt drives are easy to maintain and they do seem to last forever. Just be religious about changing oil.
With all of the vacuum processing now going on, it is much easier now to find pumps than it was 30 years ago. Also, the semiconductor fabs are going with dry pumps and existing fabs that are upgrading are getting rid of their oil sealed pumps.
Steve
Created on Monday, February 19, 2001 5:43 PM EDT by Steve Hansen