Component structure of oil free vacuum system

In recent years, it has been found that the performance and technical index of many electronic devices are seriously affected by the return of oil vapor from mechanical vacuum pump and diffusion pump into the evacuated vessel or device. For example, the oxide cathode of electronic tube reduces its emission performance and service life due to oil vapor; various high-power and high-voltage electronic tubes are easy to be broken through due to the presence of oil vapor; the high-voltage vacuum capacitors used in radio stations, due to the presence of poised steam, significantly reduce their withstand voltage index, and oil vapor has a significant adverse effect in many places. Therefore, the vacuum system used in these aspects should be replaced by an oil-free vacuum system, that is, instead of using vacuum oil sealing and vacuum oil as the working fluid (such as mechanical pump and diffusion pump), the vacuum system can be obtained by adsorption of gas molecules and reducing the pressure in the container. 

The adsorption pump uses the porous surface of some solid materials to strongly adsorb the gas in the cold state, so that the closed system can obtain a low vacuum of 10-2 mm mercury column. It is used as the front stage of oil-free system.

In addition to activated carbon, most of the adsorbents used in the adsorption pump use molecular sieve (artificial zeolite) to adsorb gas and obtain vacuum. Because, after cooling with liquid nitrogen, each kilogram of molecular sieve can pump a 50-100 liter container from the atmosphere into a vacuum of 10-2 mm mercury column. Therefore, it is a pump with large suction. After baking at about 400 ℃, the gas it absorbs will be released again (called activation or regeneration) to restore the ability of reabsorbing. At present, the commonly used 5A molecular sieves (with large absorption capacity, suitable for exhaust air, but often "activated", with an average pore diameter of about 5 angstroms) and 13X molecular sieves (although their adsorption capacity is smaller than 5A molecular sieves, they can absorb oil vapor molecules).

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