Vacuum generation
Vacuum nature and quality - Contamination

Vacuuming or evacuating a working chamber or enclosure involves reducing (in principle, by elimination) the number of molecules in the various gases present in this volume.

At normal atmospheric pressure (1.01325.10⁵ Pa), in a one-liter volume at 0°C, there are 2.7.10²² molecules and atoms of gas. In a primary vacuum, i.e. at 10^-1 hPa, this still leaves 2.7.10¹⁸ molecules, or 99.99% empty. It is the nature of these remaining molecules (i.e. 2.7.10¹⁸ per liter) that is of interest to the operator, as they are sources of poor product quality or system malfunction. If we move to a pressure level of 10^-6 hPa, there are still 2.7.10¹³ molecules per liter, which is still far too many for certain applications...