2.活塞式空气压缩机的工作原理在气压传动中，通常采用容积型活塞式空气压缩机。这里介绍两种典型结构，用来帮助理解空气压缩机的工作原理。图3.33（动画）和图3.34（动画）分别给出了立式、卧式空气压缩机的工作原理图。立式空气压缩机的气缸中心线与地面垂直，卧式空气压缩机的气缸中心线则与地面平行。原动机（电动机或内燃机）的回转运动经曲柄连杆机构转换为活塞的往复直线运动。空气压缩机中的进气、排气过程与液压泵的吸油、压油过程类似，这里不再赘述。3.空气压缩机的选择空气压缩机的选择主要依据气动系统的工作压力和流量。气源的工作压力应比气动系统中的工作压力高20%左右，因为要考虑供气管道的沿程损失和局部损失。如果系统中某些地方的工作压力要求较低，可以采用减压阀来供气。空气压缩机的额定排气压力分为低压（0.7~1.0MPa）、中压（1.0~10MPa）、高压（10~100MPa）和超高压（100MPa以上），可根据实际需求来选择。
1. Classification of air compressor the air compressor is the main body of the air source device. It is a device that converts the mechanical energy of the prime mover (usually the motor) into gas pressure energy. It is the air pressure generating device of compressed air. There are many kinds of air compressors, which can be divided into volumetric compressors and speed compressors according to the working principle. The working principle of volumetric compressor is to compress the volume of gas, increase the density of gas molecules per unit volume, and increase the pressure of compressed air; The working principle of speed compressor is to increase the movement speed of gas molecules, so that the kinetic energy of gas molecules can be converted into gas pressure energy, so as to increase the pressure of compressed air.
2. Working principle of piston air compressor in pneumatic transmission, volumetric piston air compressor is usually used. Here are two typical structures to help understand the working principle of the air compressor. Figure 3.33 (animation) and figure 3.34 (animation) show the working principle diagrams of vertical and horizontal air compressors respectively. The cylinder center line of the vertical air compressor is vertical to the ground, and the cylinder center line of the horizontal air compressor is parallel to the ground. The rotary motion of the prime mover (motor or internal combustion engine) is converted into the reciprocating linear motion of the piston through the crank connecting rod mechanism. The air intake and exhaust processes in the air compressor are similar to the oil suction and oil pressure processes of the hydraulic pump, which will not be repeated here.
3. Selection of air compressor the selection of air compressor is mainly based on the working pressure and flow of pneumatic system. The working pressure of the air source should be about 20% higher than that in the pneumatic system, because the along-line loss and local loss of the air supply pipeline should be considered. If the working pressure in some parts of the system is low, the pressure reducing valve can be used to supply air. The rated exhaust pressure of the air compressor is divided into low pressure (0.7~1.0mpa), medium pressure (1.0~10mpa), high pressure (10~100mpa) and ultra-high pressure (above 100MPa), which can be selected according to the actual demand.
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