Hi, i kow this is an old thread and i had to make a new account because i couldn't access my old one, but i tried the methode explained to me above again to calculate the pumpe time of a simmilar setup with a small chamber with only a small opening inside a regular vacuum chamber.
The regular vacuum chamber had 4 NEG pumps and one IGP. I set the surface of the inside chamber to a uniform outgasing and divided the final preasure in the inner chamber total the outgasing in the inner chamber by the and got around 6 l/s pumping speed (the 4 NEG have a pumping speed of 430 l/s each and the IGP 100l/s). Then i tried to calculate the time it takes to pump from 10^-8 mbar to 10^-11 mbar with the volume of the inner chamber. As this volume is under 1l i got something around 3 seconds, which doesn't seem correct.
Do i have to take into account, that the pumping speed of the NEGs changes with the reduction of the preasure or does anyone know where i dit a mistake, i am thinking over this for a few days and can't find what i did wrong.
Help here would be much appreciated.