Good stuff all this... one small point to add on the ultra low pressure operation with a mechanical pump. You are increasingly likelyto have serious backstreaming of roughing pump oil vapor as your pressures dip below 1E-4 torr. I think Dunniway has roughing pump vapor pressure data in their vacuum pump oil section, online. My recollection is that it is around 1E-5 Torr. So the longer you run at very low pressure on the roughing pump, the more pump oil vapor backstreaming will occur. It is also temperature dependent.
Dave Cooper
Created on Tuesday, April 17, 2001 9:15 PM EDT by David Cooper