A vacuum chamber of 500 l may have a total surface area
(including all systems) of about 5 m2. A steady gas evolution of
2 · 10-4 mbar · l/s is assumed per m2 of surface area. This is a level which
is to be expected when valves or rotary feedthroughs, for example are
connected to the vacuum chamber. In order to maintain in the system a
pressure of 1 · 10-5 mbar, the pump must have a pumping speed of