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The concept of compressed air has been around ever since humans learned how to blow on a fire to keep it going. But let’s skip ahead to the first mechanical compressor, which was actually not a compressor like we know today. Back in the day, they were manually controlled bellows, the very first mention of an actual piston compressor dates back to the end of the 18th century. With modern technology, piston compressors have been greatly improved and even to this date they are one of the most popular air compression technologies available.
Above, you can take a look at the cross-section of a basic piston compressor and its parts. However, you might ask yourself how these parts actually work together in creating compressed air. It all starts with the intake phase. During the intake phase the piston descends, sucking the air through the filter. The air then passes through the inlet valves, into the cylinder. At this point, the discharge valves are closed. When the piston ascends again, the air in the cylinder gets compressed. Simultaneously, the inlet valves close and the discharge valves reopen to allow the air to discharge. This is called the outlet phase.
In theory, all piston compressors work according to the same principle. However, there are major differences in how the compressor puts this principle to use. The main one is the number of stages in which the compression takes place. There are single-stage, double stage, and multi-stage compressors. Dividing the compression over different stages reduces the compressor work and final air temperature (the process then gets closer to an isothermal one). In order to get the full benefits from multi-stage compression, the air needs to be cooled between the different stages. This can be done with the help of an intercooler.