Your results will be interesting. I've never inserted a trap between my mechanical and diffusion pumps. I think that the purpose of doing this would be more to prevent cross contamination of the pump oils (mech pump oil backstreaming to the diffusion pump) rather than mitigating water vapor. However, you can minimize any potential backstreaming by operating the system as much as possible with your gas supply bleeding into the chamber. This will help you to avoid molecular flow conditions, especially in the foreline. But, even with some backstreaming it'll take a long time to contaminate your dp oil.
Steve
Created on Sunday, April 15, 2001 11:25 PM EDT by Steve Hansen