There are many ways to classify air compressors. According to the exhaust volume, there are micro air compressors, small air compressors, medium air compressors and large air compressors. According to the working principle, it is divided into positive displacement air compressor and speed air compressor, such as piston air compressor, screw machine, sliding vane machine, scroll air compressor, which are typical positive displacement air compressors; Centrifugal air compressor, axial air compressor and jet air compressor are speed air compressors.  
So, for air compressor users, how to choose a suitable air compressor among many air compressors? First, fully consider the requirements of gas consumption. The selected air compressor must meet the requirements of production process, specifically, the outlet pressure, exhaust volume, exhaust temperature and gas quality of the air compressor must meet the requirements of use.  
1. Select an air compressor with appropriate exhaust volume. For an enterprise or gas consumption unit, the actual gas consumption of the gas consumption system includes the gas consumption of existing equipment, the leakage of pipelines, and the gas reserve of pipelines. If Qmax is used to represent the maximum air consumption of the pneumatic system, QSA is the average air consumption of the pneumatic system, and Q is the air consumption, then when there is an air tank, the air consumption q= (1.5~1.8) QSA; Without air storage tank, the gas consumption q= (1.5~1.8) Qmax. Considering the leakage of pneumatic components, pipe joints, etc., the estimation error of air consumption of pneumatic system, the utilization rate of multiple pneumatic equipment used at the same time, and the possibility of adding new pneumatic equipment, the air consumption Q should be increased appropriately. Generally speaking, the exhaust volume of the air compressor should match the air consumption you need, and 10% of the space should be reserved.  
2. Select an air compressor with appropriate air outlet pressure. From the perspective of use, the output pressure of the air source should be about 20% higher than the maximum working pressure in the pneumatic system. According to national standards, the design pressure of pneumatic tools is 0.4MPa (0.1mpa=1kg), while the rated exhaust pressure of general-purpose air compressors is 0.7mpa~0.8mpa, which can fully meet the air requirements of pneumatic tools. If the working pressure in some parts of the system is low, the pressure reducing valve can be used to supply air. If the compressed air pressure required by the user is greater than 0.8MPa, it cannot be obtained by forcible pressurization, and the air compressor with large outlet pressure must be selected. 3. Select the appropriate post-treatment system of compressed air. The compressed air produced by the ordinary air compressor contains a certain amount of lubricating oil and water.  
For general gas use, compressed air can be used by connecting it to gas facilities through gas pipelines. However, some gas use occasions are oil-free and water-free, and some gas use occasions also have strict requirements on air temperature. At this time, attention should be paid not only to the selection of air compressor, but also to the post-processing device of compressed air if necessary. For users who have high requirements for oil content of gas, there are two gas solutions: one is to use oil-free air compressor, which produces gas with oil content of basically zero, and it is widely used in pharmaceutical, textile and other industries that need clean gas source; The second solution is to configure corresponding primary or secondary purification devices. Users who require high water content in the air can install a dryer to dry the compressed air before use. Generally speaking, after two-stage purification and drying, the amount of oil and water in the compressed air can be basically controlled below 5ppm. In addition, if there are no special requirements for the temperature of compressed air, be sure to use a frozen dryer with heat recovery.