Evacuation of a chamber in the high vacuum region

The gas quantity Q consists of the sum of all the gas evolution and all leaks possibly present. Whether it is from gas evolution or leakage may be determined by the following method  

If the gas evolution Q and the required pressure Pgi j are known, it is easy to determine the necessary effective pumping speed  

Example A vacuum chamber of 500 I may have a total surface area (including all systems) of about 5 m. A steady gas evolution of 2 10 mbar l/s is assumed per m 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 mbar, the pump must have a pumping speed of 

A pumping speed of 100 l/s alone is required to continuously pump away the quantity of gas flowing in through the leaks or evolving from the chamber walls. Here the evacuation process is similar to the examples given in Sections 2.3.1.1. However, in the case of a diffusion pump the pumping process does not begin at atmospheric pressure but at the 

In order to attain an ultimate pressure of 1 10 mbar within 5 minutes after starting to pump with the diffusion pump an effective pumping speed of 

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