Oil diffusion pump is the main equipment to obtain high vacuum. It is widely used in vacuum smelting, vacuum coating, space simulation test and some vacuum systems insensitive to oil pollution. The oil diffusion pump is mainly composed of pump body, diffusion nozzle, steam conduit, oil pan, heater, diffuser, cooling system and jet nozzle.
When the oil diffusion pump is pre pumped to a vacuum of less than 1 pa, the oil pan can start heating. When boiling, the nozzle ejects a high-speed steam stream, and the heat-moving gas molecules diffuse into the steam stream, colliding with the directionally moving oil vapor molecules. The gas molecule therefore gains momentum and generates directional flow that is the same direction as the movement of oil vapor molecules. At the front stage, the oil vapor is condensed and the gas molecules are released, which is pumped by the front stage pump to achieve the purpose of pumping gas.
The vapor pressure of the pump directly affects the vacuum performance of the pump. However, any pump oil used by the oil diffusion pump is a mixture of different components with different vapor pressure. Therefore, in order to improve the pumping and vacuum performance of the oil diffusion pump, the pump itself has to fractionate and purify the pump oil. The purpose of fractionation is to keep the oil of high vapor pressure components from entering the high vacuum working nozzle (the nozzle at the high vacuum end); the purpose of purification is to make the oil of high vapor pressure components be continuously removed by the front pump during the working process, so that the oil gradually tends to be pure.
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