Thanks Forum and your help....

I have not filled my system yet.

I had a small little vacuum pump which I used and it has reached a pressure of 25 inch of Hg or about 10^-2 mbar. I now have a bigger pump which should go down to 10^-3 mbar.

I could get a research grade pump which will get me down as far down as 10^-6 mbar. However, the limitation is going to be the piping and the connections etc...

What is the pressure one would recommend to reach before filling the system. I pumped on the system for more than 24 hours ...

I can not imagine that the backgroung pressure can be that critical for the system performance...I can get it down to whatever seems feasilbe... but I can not imaging that it would go below 10^-5 mbar due to the rubber hoses and seals...

Any insight woudl be appreciated....