PUMPS FOR ROUGH AND HIGH VACUUM

Because of the factors described above, an assessment of the pump-down time must be basically different for the evacuation of a container in the rough vacuum region from evacuation in the medium- and high vacuum regions. 

In general, demountable joints In metallic vacuum components, pumps, valves, tubulatlons, and so on are provided with flanges. Vacuum components for rough, medium, and high vacuum from LEYBOLD are equipped with the following standardized flange systems ... 

The areas of application for these vacuum pumps are all within the rough and medium vacuum range, the principal vacuum range for chemistry processes. Only the short path and molecular distillation processes rely also high-vacuum pumps like the diffusion pump or even the turbomolecular pump (kinetic gas pumps). High-vacuum pumps are not covered in this book. For these refer to [2, 3]. 

In the rough vacuum region, the volume of the vessel is decisive for the time involved in the pumping process. In the high and ultrahigh vacuum regions, however, the gas evolution from the walls plays a significant role. 

This chapter is primarily devoted to pumps for high vacuum-operation (10 3-10 5 torr), which is the vacuum range of greatest interest in chemical vacuum lines. In addition, rough-vacuum systems (760-0.1 torr) are discussed in connection with their use in manipulating mercury-filled apparatus, such as Toepler pumps and McLeod gauges. 

Such pumps are gas-transfer pumps. They are used extensively both to back high-vacuum pumps and to act as devices for achieving pressures in the rough-medium range in activities such as distillation, drying, etc. 

The equipment required to apply all these PVD methods works at pressures lower than ambient pressure this is necessary in order to control the composition of the deposited material. To improve its purity, the mean free path of the particles must be greater than the distance between the source and the substrate. In the specific case of TE, this also allows a lower operational temperature for the vaporization. A conventional deposition system consists of a vacuum chamber, a mechanical roughing pump, a high vacuum pump, a heated crucible and a substrate holder. 

Some who specialize in vacuum technology use the following gradation system for levels of vacuum coarse vacuum (760 to 1 Torr absolute), rough vacuum (760 to 0.001 Torr absolute), high vacuum (10 to 10 Torr absolute), and ultra high vacuum (10 to 10 Torr absolute). To get to any pressure below lO Torr absolute requires more than one vacuum pump. 

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