Note chosen a vacuum pump, vacuum pump pressure should limit the process to meet the pressure of work. Usually choose the pump pressure is below the limit process requirements about one order of magnitude. 2. Each pump has a certain working pressure range, and therefore, the pump operating point should be selected within this range, but can not get it to work long hours outside the allowable working pressure. 3, a vacuum pump at its working pressure, should be able to discharge all of the amount of gas pump equipment produced in the process. 4. Select the vacuum unit: (1) When using a suction and vacuum pump can not meet the requirements, you need a combination of several pumps, complement each other in order to meet the technical requirements. (2) a little pump is not working at atmospheric pressure, you need to pre-vacuum; some pump outlet pressure below atmospheric pressure, you need to pre-stage pump, the ancient capital of the need to combine the use of the pump. After the vacuum pump used in combination, which we call the vacuum pump unit, he can get a better vacuum system vacuum degree and displacement. We should select the right combination of a vacuum pump, a vacuum pump of the gas due to the different requirements of different pumping requirements, such as: In general Roots - Unit not available for spin-condensable gases contain more systems. 5. When you select a pump seal, you should first find out if your vacuum system for oil pollution requirements. If the device when no oil strict requirements, you should choose a variety of non-oil pump, such as: water ring pumps, cryogenic pumps. If the requirements are not strict, you can choose a pump, plus some oil pollution prevention measures, such as adding cold trap, gear oil wells, baffles, etc., but also to achieve clean vacuum requirements. 6. Learn to be pumping gas composition, gas containing free of condensable vapor, with or without dust particles, with or without corrosive. When selecting a vacuum pump, you need to know the gas composition, select the appropriate pump is pumping gas for. If the gas contained in the vapor, particles, and corrosive gases should consider the installation of auxiliary equipment at the inlet piping of the pump, such as a condenser, a filter and the like. 7, when selecting seal vacuum pump, vacuum pump discharge to be considered out of the oil vapor (fumes) affect on the environment. If the environment does not allow pollution, should choose oil-free vacuum pump, or the oil vapor outside. 8, the vibration generated when the pump working on the process and whether the impact of the environment, if the process does not allow the pump should be selected without vibration or take anti-vibration measures. 9, vacuum prices, operating and maintenance costs. After we consider the arrival of this case, in order to finalize a solution adapted to your; viable options (1) The minimum investment costs (2) The minimum production run costs (3) The first two cases reasonably evenly distributed.