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The working pressure of the vacuum pump should satisfy the limit vacuum and the working pressure requirement of the vacuum equipment. Such as: vacuum coating required 110-5mmHg vacuum, vacuum pump selected at least 510-6mmHg. The vacuum of the pump is usually higher than that of the vacuum. The vacuum is half an order of magnitude.

The correct choice of the vacuum pump, each pump has a certain working pressure range, such as: diffusion pump for 10-3~10-7mmHg, in such a wide range of pressure, the pumping speed varies with pressure, the stable working pressure range of 510-4~510-6mmHg. Therefore, the working point of the vacuum pump should be chosen within this range, and not allow it to work under the 10-8mmHg for a long time. Another example is titanium sublimation pump which can work under 10-2mmHg, but its working pressure should be less than 110-5mmHg.