Working pressure pW
During evacuation the gases and/or vapors are removed from a vessel.
Gases are understood to be matter in a gaseous state which will not, however,
condense at working or operating temperature. Vapor is also matter in
a gaseous state but it may be liquefied at prevailing temperatures by
increasing pressure. Finally, saturated vapor is matter which at the prevailing
temperature is gas in equilibrium with the liquid phase of the same substance.
A strict differentiation between gases and vapors will be made in the
comments which follow only where necessary for complete understanding