ABSTRACT
The function of a vacuum pump is to withdraw gas from a designated volume so that the pressure is lowered to a value suitable for the purpose in hand. The variety of applications of vacuum technology is such that a very wide range of vacua has to be provided. Thus a very modest vacuum of only 100 mbar is sufficient to enable large forces based on the 900-mbar pressure difference with atmospheric pressure to be used in vacuum molding. But a pharmaceutical application may require the maintenance of 10−2 mbar with high flow rates of water vapor, and the vacuum coating of mirror surfaces by the condensation of metallic vapor from hot vaporization sources needs a high vacuum of less than 10−5 mbar to be held with large outgassing loads. An ultrahigh vacuum ~10−10 mbar is necessary to secure adequately clean conditions for investigations in surface science.
