About the compression ratio of the air compressor?

Update:22-03-2021
Summary:

(Pressure ratio, pressure ratio) Ⅰ Internal compression […]

(Pressure ratio, pressure ratio)
Ⅰ Internal compression ratio (ie internal pressure ratio)
The ratio of the final pressure (absolute pressure) of the gas after internal compression to the initial pressure (absolute pressure).
Ⅱ External compression ratio (ie external pressure ratio)
The ratio of the compressor outlet discharge pressure (absolute pressure) to the inlet suction pressure (absolute pressure).
For screw air compressors, the internal compression ratio refers to the pressure ratio between the suction and exhaust ports of the screw main engine (absolute pressure), and the external compression ratio refers to the pressure ratio between the suction and exhaust ports of the air compressor (absolute pressure) .
Generally speaking, the compression ratio of an air compressor refers to the external compression ratio, the suction pressure refers to the local atmospheric pressure, and the exhaust pressure refers to the rated working pressure of the air compressor. If the exhaust pressure is 8bar, the compression ratio is 9.
For multi-stage compressors, the pressure ratio is also called the total pressure ratio, which refers to the ratio of the exhaust pressure measured at the final stage of the exhaust pipe to the suction pressure measured at the first stage of the intake pipe. The ratio of the nominal suction and discharge pressures of the corresponding levels is called the pressure ratio of the level.