Working pressure of vacuum pumpIn the process of using the vacuum pump, its working strength should meet the requirements of the limit vacuum and working pressure of the vacuum equipment. For example, vacuum coating requires a vacuum degree of 1 × 10-5mmhg, and the vacuum degree of the selected vacuum pump shall be at least 5 × 10-6mmhg. Generally, the vacuum degree of the pump is half to one order of magnitude higher than that of the vacuum equipment.The correct choice of the working point of the vacuum pump, each pump has a certain range of working pressure, such as: diffusion pump is 10-3 ~ 10-7mmhg, in such a wide range of pressure, the pumping speed of the pump changes with the pressure, the stable working pressure range is 5 × 10-4 ~ 5 × 10-6mmhg. Therefore, the working point of the pump should be selected within this range, and it cannot be allowed to work for a long time under 10-8mmhg.Under its working pressure, the vacuum pump should be able to discharge all the gas produced in the process of vacuum equipment. Combine the vacuum pump correctly. Because of the selective pumping of vacuum pump, sometimes selecting one pump can not meet the pumping requirements. Several pumps need to be combined to supplement each other to meet the pumping requirements. For example, the titanium sublimation pump has a very high pumping speed for hydrogen, but it can't pump helium, while the three pole sputtering ion pump (or the two pole asymmetrical cathode sputtering ion pump) has a certain pumping speed for argon, and the combination of the two will make the vacuum device get a better vacuum degree. In addition, some vacuum pumps can't work under atmospheric pressure and need pre vacuum; some vacuum pumps need pre stage pumps because the outlet pressure is lower than atmospheric pressure, so they need to be combined for use.Requirements of vacuum equipment for oil pollution. If the equipment is strictly oil-free, various oil pumps should be selected, such as: water ring pump, molecular sieve adsorption pump, sputtering ion pump, low temperature pump, etc. If the requirements are not strict, oil pump can be selected, and some anti oil pollution measures, such as cold trap, baffle, oil trap, etc., can also meet the requirements of clean vacuum.