What is the working principle of two stage compressor?

1. Step 1: Air intake and primary compression (low pressure stage)

 Air Filtration : Ambient air (approximately 0.1MPa) first enters the air filter, which removes particulate contaminants such as dust and impurities (typically with a filtration precision of 1-5μm). This prevents wear on the cylinder or contamination of the compressed air.

 Low pressure compression : The filtered clean air enters the low-pressure cylinder , where the reciprocating motion of the piston compresses the air volume and increases its pressure (typically from 0.1MPa to 0.3-0.5MPa), completing the first compression. During this process, significant heat is generated, with temperatures reaching 120-160°C.

2. Step 2: Intermediate Cooling to Reduce Air Temperature and Energy Consumption. This is the key difference between two-stage compression and single-stage compression—the intermediate cooler(typically a shell-and-tube or finned heat exchanger) forcibly cools the high-temperature air after primary compression.

-The cooling medium (usually cooling water or cooling air) exchanges heat with the high-temperature compressed air, reducing the air temperature from 120-160℃ to 40-50℃ (close to ambient temperature).

-The cooling air density is significantly increased and the molecular activity is reduced, which can not only reduce the "push resistance" of the subsequent secondary compression, but also avoid the loss of high temperature on the secondary cylinder sealing and lubricating oil, and indirectly reduce the energy consumption and equipment failure rate.

3. Third Stage: Secondary Compression to Target Pressure (High-Pressure Stage) The cooled low-pressure air (0.3-0.5MPa) enters the high-pressure cylinder, where the high-pressure piston further compresses it to achieve the target industrial pressure (typically 0.7-1.3MPa, with some high-pressure models exceeding 3MPa), completing the second compression stage. Since the primary compression has already reduced pressure, the "compression ratio" (exhaust pressure/absorption pressure) in the secondary compression is significantly lower than single-stage compression (typically 2-3:1). This gradual compression process enhances energy conversion efficiency by minimizing waste heat and maximizing the conversion of electrical energy into compressed air potential energy.

4. Step 4: Oil-Gas Separation and Air Purification. Two-stage air compressors typically employ oil lubrication (some oil-free models use dry compression). During compression, lubricating oil mixes with air, requiring separation and purification through an oil-gas separator.