Molecular Seive for making vacuum tubes

[Y2keddie]

im trying to jog my memory back 30years when I worked with vacuum tubes. I worked with manufacturing of image tubes. I remember the vacuum systems used vac-ion pumps to achieve -12 power torr. I alsoo remember first using a molecular seive for roughing,pumping to 10 microns.
The seive was a canister filled with a zeonolite which was cooled with liquid nitrogen.
I believe it worked as an adosorbtion process where water molecules would adhere to the zenolite surface thus removing water molecules from air in the beginning stages of vacuum.
What my memory is fuzzy about: is the seive used just for water,or other gas molecules?

 

[trurle]

Zeolites do adsorb nitrogen at liquid-nitrogen temperatures, too. Main purpose of cool traps is to adsorb oil molecules leaking from roughing oil pumps though.
http://www.phys.ufl.edu/REU/2008/reports/magee.pdf

 

[Y2keddie]

My recall is not that good. I’m guessing the process sequence was:

Use Mechanical pump ( to 10 microns).
Isolate
Then molecular Seive (to ?? Torr) The decrease in pressure would indicate the oil molecules had decreased?
Isolate
Then Vac Ion pump to 10x-14 torr

That would make sense. The oil contaminants would destroy the tubes cathode properties.