When you’re designing a vacuum system, it is important to select a vacuum system that will evacuate the chamber and associated piping in a prescribed amount of time. This is essential in a production environment where the time to complete a process has quite a lot to do with the cost of the manufactured part.
“To calculate the evacuation time for a vacuum chamber, numerous physical factors must be taken into account, i.e. conductance, thermal effects, pumping speed, etc. For a quick estimate, however, it is often sufficient to perform a segmented use of the following formula: t = (V / S) * ln(p1 / p2).”
Source: Vacuum Science World