Selection of vacuum pumps

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Here is the citation: The function of an air pump is to remove gas molecules from the vacuum chamber, thereby reducing the gas pressure inside it and achieving the desired level of vacuum. In general, there is a wide range from the atmosphere to ultra-high vacuum, and to date no vacuum system has been able to cover this entire range. Therefore, to meet the requirements regarding process parameters, work efficiency, and equipment service life for different products, different vacuum system configurations must be selected for various vacuum sections. To achieve the optimal configuration, the following points should be considered when selecting a vacuum system: Determining the operating vacuum range: It is first necessary to identify the vacuum level required for each process. Since each process has its own suitable range of vacuum levels, it is necessary to carefully study and determine them. Determine the ultimate vacuum level: Based on the vacuum level required by the process, check the ultimate vacuum capacity of the vacuum pump system, as it is the ultimate vacuum capacity that determines the optimal operating vacuum level for the system. Generally speaking, the ultimate vacuum of the system is 20% lower than the operating vacuum of the system, and 50% lower than the ultimate vacuum of the pre-pump. Type of gas to be evacuated and evacuation volume: Determine the type of gas to be evacuated and the required evacuation volume based on the process requirements. Because if the type of gas being pumped reacts with the liquid inside the pump, the pump system will become contaminated. At the same time, it is necessary to consider determining an appropriate exhaust time and the amount of gas generated during the pumping process. Vacuum volume: Checks to determine the time required to achieve the desired vacuum level, as well as the flow resistance and leaks in the vacuum piping. Consider the pumping rate required to maintain the vacuum under certain process conditions after achieving the desired vacuum level. 〖Calculation for selecting the main vacuum pump〗 S=2.303×V/(t×Log(P1/P2)), where: S is the pumping speed of the vacuum pump (L/s); V is the volume of the vacuum chamber (L); t is the time required to achieve the desired vacuum level (s); P1 is the initial vacuum level (Torr); P2 is the desired vacuum level (Torr). For example, if V=500 L, t=30 s, P1=760 Torr, and P2=50 Torr, then: S=2.303×500/(30×Log(760/50)) = 35.4 L/s. Of course, this value is only a theoretical calculation; there are several factors that have not been taken into account, such as pipeline flow resistance, leaks, the flow resistance of filters, and the temperature of the gas being pumped. In fact, the safety factor should also be taken into account.