Common air compressor working principle

Compressor, a driven fluid machine that upgrades low-pressure gas to high-pressure gas, is the heart of the refrigeration system and is divided into: piston compressor, screw compressor, centrifugal compressor, rotor compressor, axial flow compressor, slide compressor tablet compressor etc.

1. Piston compressor

The work of the piston compressor is completed by the continuous change of the working volume formed by the cylinder, the valve and the piston reciprocating in the cylinder. If the volume loss and energy loss in the actual work of the piston compressor are not considered (that is, the ideal working process), the work completed by the crankshaft of the piston compressor per revolution can be divided into suction, compression and exhaust processes.

Working principle of piston compressor

Compression process: the piston moves upward from the bottom dead center, the suction and exhaust valves are closed, and the gas is compressed in the airtight cylinder. As the volume of the cylinder gradually decreases, the pressure and temperature gradually increase until the gas pressure in the cylinder is the same as that of the exhaust gas. The pressure is equal. The compression process is generally regarded as an isentropic process.

Exhaust process: The piston continues to move upwards, causing the gas pressure in the cylinder to be greater than the exhaust pressure, then the exhaust valve opens, and the gas in the cylinder is pushed by the piston and discharged from the cylinder into the exhaust pipe at equal pressure until the piston moves to the top point. At this time, due to the effect of the spring force of the exhaust valve and the gravity of the valve plate itself, the exhaust valve is closed and the exhaust is completed.

2. Screw compressor

Screw compressors, also known as screw compressors, are divided into single-screw compressors and twin-screw compressors. The single-screw compressor was developed by Sinn of France in the 1970s. Because of its more reasonable structure, it was quickly applied to the field of national defense and protected by the developing country. The technology has always been relatively independent. The twin-screw compressor was first proposed by the German H.Krigar in 1878. It was not until 1934 that A.Lysholm of the Swedish Royal Institute of Technology established the SRM technology of the screw compressor, and began to be applied in industry, and achieved rapid development.

Working principle of screw compressor

The screw compressor cylinder is equipped with a pair of intermeshing helical male and female rotors. Both rotors have several concave teeth, and the two rotate in opposite directions.

The gap between the rotors and between the casing and the rotor is only 5~10 wires. The main rotor (also known as male rotor or convex rotor) is driven by the engine or electric motor (mostly driven by electric motor), and the other rotor (also known as The female rotor or the female rotor) is driven by the oil film formed by the main rotor through oil injection, or by the synchronous gear at the main rotor end and the female rotor end.

So there is no metal contact in the drive (in theory). The length and diameter of the rotor determine the displacement (flow) and discharge pressure of the compressor. The longer the rotor, the higher the pressure; the larger the diameter of the rotor, the greater the flow.

3. Centrifugal compressor

Centrifugal compressors, also known as turbo compressors, are mainly used to compress gases and are mainly composed of rotors and stators. The rotor includes an impeller and a shaft. The impeller has blades, a balance disc and a part of the shaft seal; the main body of the stator is a cylinder, and there are devices such as a diffuser, a bend, a reflux, an air inlet pipe, and an exhaust pipe.

Working principle of centrifugal compressor

When the impeller rotates at high speed, the gas rotates with it. Under the action of centrifugal force, the gas is thrown into the diffuser behind, and a vacuum zone is formed at the impeller. At this time, the fresh gas from the outside enters the impeller. The impeller rotates continuously, and the gas is continuously sucked in and thrown out, thus maintaining a continuous flow of gas.

4. Rotary compressor

The rotor compressor is driven by an engine or an electric motor (mostly driven by an electric motor), and another rotor (also known as a female rotor or a concave rotor). It is driven by the oil film formed by the main rotor through oil injection, or by the synchronous gear at the main rotor end and the female rotor end.

Working Principle of Rotary Compressor

The helical rotor grooves are filled with gas when they pass through the suction port. When the rotor rotates, the rotor groove is closed by the casing wall to form a compression chamber. When the rotor groove is closed, lubricating oil is sprayed into the compression chamber to play the role of sealing, cooling and lubrication.

When the rotor rotates and compresses lubricant + gas (referred to as oil-air mixture), the volume of the compression chamber decreases, and the oil-air mixture is compressed to the exhaust port. When the compression chamber passes through the exhaust port, the oil-air mixture is discharged from the compressor, completing a suction-compression-exhaust process.

5. Axial flow compressor

Axial flow compressor is a kind of large air compressor, the maximum power can reach 150,000KW, the displacement is 20,000 cubic meters per minute, and its energy efficiency ratio of the compressor can reach about 90%, which is more energy-saving than the centrifuge .

Axial flow compressors and centrifugal compressors are both speed type compressors and both are called turbo compressors.

The meaning of speed-type compressors means that their working principle relies on the blades to do work on the gas, and first greatly increases the flow velocity of the gas, and then converts kinetic energy into pressure energy. The meaning of turbo compressors is It means that they all have high-speed rotating blades.

6. Sliding vane compressor

The sliding vane compressor is directly driven at a very low speed. The rotor is the only continuously running part. There are several slots cut along the length on it, and the sliding vanes that can slide on the oil film are inserted in it. The rotor is in the stator of the cylinder. Rotate.

Working principle of sliding vane compressor

The air is sucked in through a filter and a regulating proportional valve, which is mainly used to regulate the air cylinder rotor and the pressure chamber formed by the sliding plate.

The rotor rotates eccentrically with respect to the cylinder, the valve plate is installed in the groove of the rotor, and the slide plate is pushed to the cylinder wall by centrifugal force. The efficient oil injection system can ensure the cooling of the compressor and the minimum loss of lubricant. A thin film of oil formed on the metal can prevent direct contact between metal parts and cause wear.

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