In the design and calculation of the vacuum system, the vacuum pump that directly evacuates the vacuum container is called the main pump, and the vacuum pump that maintains the foreline pressure of another pump below the critical foreline pressure is called the foreline pump. In order to quickly pump the vacuum pump from the atmospheric pressure to the pressure where the main pump can start working, it is called a pre-pumping vacuum pump. For a vacuum system, the backing pump of the system is often doubled as a pre-vacuum pump. The pump selection mentioned here refers to the selection of the main pump. Regarding pump allocation, in a narrow sense, it refers to the correct matching of the main pump with a reasonable backing pump, and in a broad sense, it includes the selection of the backing pump and the pre-pumping pump. The core equipment in the vacuum system is the vacuum pump, and the key step in the design of the vacuum system is the selection and distribution of the pump.

The specific content of the pump selection is to determine the type of the main pump and determine the size of the main pump. The principles of pump selection are technologically reliable, economically reasonable, technologically advanced, system-optimized, and form-art.

To determine the type of the main pump, the first thing to consider is the feasibility and reliability. It should be based on the ultimate vacuum degree and working vacuum degree to be achieved by the vacuum pump (the ultimate vacuum degree of the main pump is slightly higher than the ultimate vacuum degree of the vacuum chamber), according to the pumped gas. The type, the proportion of each gas, and the inclusion of dust in the gas, etc., select the vacuum pump that meets the process requirements. When two or more different types of pumps are suitable for the above conditions, an economically reasonable vacuum pump should be selected according to economic indicators such as initial investment and daily maintenance costs. Then, further compare the environment and other conditions, and select the best one. For this reason, it is necessary to start from the entire vacuum system and consider it comprehensively, and it must not be determined just by comparing the vacuum pump.

The size of the main pump is determined according to the working pressure required by the vacuum chamber and the maximum exhaust volume in the chamber. The working pressure in the vacuum chamber must be selected within the optimum pumping speed pressure range of the main pump. In addition, the size of the vacuum chamber and the pumping time should also be considered, because under a certain pumping time, the larger the vacuum chamber volume, the greater the pumping speed of the main pump.