In the application of vacuum system, the extracted gas not only includes all kinds of gases produced in the application process, but also includes the original atmospheric air in the system.
1. Gas generated in the process of vacuum system
It includes gases emitted by materials in the process and gases introduced as required by the process, as well as gases evaporated by liquid or solid in the vacuum system. The calculation of the amount of gas in this part is different for different process and different materials.
2. Atmospheric gas originally existing in the vacuum system
In the vacuum system, the vacuum container chamber and vacuum tube circuit, etc., originally contain a certain amount of atmospheric gas components. In the initial stage of pumping, they are the main gas load of the vacuum system pumping, and they are also drained early by the system z*.
3. Leakage gas in vacuum system
The leakage gas includes the air leaking into the vacuum system through the connection of vacuum seal and various leakage channels. For a given vacuum system, the amount of gas leaking is a constant. Different vacuum system applications, different limit pressure, the amount of gas leakage also has a strict limit.
4. Gases released by surface desorption of various materials in a vacuum system
Under normal pressure, the surface of the material in the vacuum system will absorb and dissolve part of the gas. At negative pressure, this part of the gas will be released again. Its air discharge rate is related to material performance, treatment process and material surface state.
5. The air outside the vacuum system penetrates into the system through the wall material.
Gases also dissolve and penetrate in solids. Therefore, the atmosphere can permeate some gases into the vacuum system through the structural materials of the container wall. This kind of permeation can not be considered in general metal system, but some applications in glass vacuum system or thin-wall metal system will need to consider the influence of permeation gas.
The above five aspects constitute the total pumping load of the vacuum system.