When designing or operating a vacuum system, it is critical to consider several factors. Knowing the intended use will allow you to determine the technology, lubrication, chemical resistance, vacuum level, and necessary flow rate. Vacuum pumps are categorized by their operating pressure. Within each pressure range are several different pump types, each employing a different technology, and each with some unique advantages in regard to pressure capacity, flow rate, cost, and maintenance requirements.
“Vacuum Level: The pump selection heavily depends on the level of vacuum that needs to be obtained. Typically, the different pressure ranges in vacuum technology are defined as follows: Rough vacuum (from 10 3 mbar to 1 mbar); Medium vacuum (1 mbar to 10 -3 mbar); High vacuum (10 -3 mbar to 10 -7 mbar); Ultra-high vacuum (10 -7 mbar to 10 -12 mbar); Extreme high vacuum (less than 10 -12 mbar).”
Source: Vacuum Science World