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In the process of reasonable selection of vacuum pump, the middle ring vacuum pump can be selected according to the working pressure required by the specific process and the nature of the suction gas. Generally, the working pressure required by the specific process is determined first. The vacuum degree required by the process of negative pressure distillation, distillation and sublimation is high (the working pressure is low), and the vacuum degree required by the process of negative pressure evaporation, drying, concentration, crystallization, dehydration, decoloration, chemical reaction absorption and vacuum transportation of materials is low (high working pressure). After the working pressure is determined, the vacuum pump can be selected reasonably according to the size of the suction gas and the nature of the suction gas.

1. According to the working pressure that several vacuum pumps can reach, the application scope of various vacuum pumps is listed.

2. Suction different gas, choose different jet vacuum pump

a. The water jet vacuum pump is suitable for pumping various gases with working pressure greater than 25mmhg (3.3kpa). When the working pressure requirement is relatively small and the amount of non condensable gas is large, steam jet pump and steam water series and steam water combined jet vacuum pump should be selected.

b. The working pressure of steam water series jet vacuum pump can reach 2 mmHg (267 PA), but it has less pumping capacity than the new high efficiency steam jet vacuum pump, steam water combined jet vacuum pump and multi-stage steam jet vacuum pump, which is suitable for the intermittent production of small and medium-sized enterprises.

c. The working pressure of the new type of high-efficiency steam jet vacuum pump can reach 0.5mmhg (65pa), which is suitable for the process where most of the extracted gas is condensable and the proportion of non condensable gas is relatively small.

d. The working pressure of steam water combined jet vacuum pump and multi-stage steam jet vacuum pump can reach less than 10 Pa and can pump various gases. The difference between them is that steam consumption and operation cost can be saved compared with multi-stage steam jet vacuum pump.