Glass diffusion pump vacuum system

 A vacuum pump for vacuum is obtained. Vacuum pumps are classified into two types according to different working conditions: A vacuum pump capable of operating at atmospheric pressure is called a primary pump (such as a mechanical pump), and a vacuum pump for generating a preliminary vacuum, which needs to be operated under preliminary conditions, is called a secondary pump (glass). Diffusion pump), the secondary pump is used to further increase the vacuum and obtain a high vacuum.

       Vacuum section: 1 rough vacuum 760 ~ 10 Pa; 2 low vacuum 10 ~ 10 - 2 Pa; 3 medium vacuum 10 - 2 ~ 10 - 4 Pa; 4 high vacuum 10-4 ~ 10-7Pa; 5 ultra high vacuum 10 - 12 ~ 10 - 14 Pa; glass diffusion pump structure shown in Figure 1, the diffusion pump is a high vacuum pump, when the ultimate vacuum of the mechanical pump can not meet the requirements, usually a diffusion pump is added to obtain a high vacuum. This type of pump does not work from normal air pressure and can only operate at pressures below 1 Pa. Therefore, it must be used in series with the primary pump.

       There are many kinds of liquid oils for the diffusion pump. Currently, the diffusion pump oil of No. 3 (the saturated vapor pressure at 20 °C is 1.3×10-6 Pa) and the boiling point of 375 °C and No. 275 silicone oil (the saturated vapor pressure at 20 °C is 1.3). ×10- 8 Pa) The boiling point is 430 °C. Before the diffusion pump starts to work, the mechanical pump must be started to pump air. When the pre-vacuum is reached (about 1.3 Pa), the oil in the diffusion pump evaporator can be heated by the electric furnace. It can be observed in about 25 to 35 minutes. At this point, the diffusion pump oil begins to boil, and the oil vapor begins to eject toward each stage nozzle to form a jet.

When the silicone oil is heated to boiling at 430 ° C, a large amount of oil vapor is generated, and the steam is ejected from the nozzles at high speed through the conduit. At this time, since the gas from the pumped container continuously diffuses into the steam flow, it is called a diffusion pump. The jet is ejected to the lower umbrella cap. The pressure of this jet is stronger than that of the upper jet, and the gas molecules enter the next-stage jet. This level of pressure is greater than the upper jet, and the oil vapor is condensed by the condensate jacket. Flowing back along the tube wall through the return line to the evaporator, the gas carried underneath is pumped away by a mechanical pump at a rate of 4 liters per second, and the ultimate vacuum of the diffusion pump can be reached after 20 minutes. These working conditions are only easily observed through the glass, the process of diffusion, eruption and condensation, which is the origin of the name of the diffusion pump, which is invisible to these working state metal diffusion pumps.

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