Air compressors find application in numerous businesses and industries, serving a wide range of purposes, including vehicle body painting and food manufacturing. There are primarily two distinct types of air compressors: screw air compressors and piston air compressors. However, what sets these two apart from each other? Let’s introduce them first.

What is screw air compressor?

A screw compressor sucks in refrigerant through a toothed space formed by the meshing of a male rotor composed of 5 convex teeth (hereinafter referred to as the M rotor) and a female rotor composed of 6 concave teeth (hereinafter referred to as the F rotor), and compresses the refrigerant to a predetermined pressure by reducing the toothed space. The workflow of a screw compressor is as follows:

Suction stroke

Suck in refrigerant from the intake opening in the axial to radial direction. As the rotor rotates, on the lower side of the rotor, the meshing separates, the length of the tooth groove increases, and the refrigerant is sucked into the tooth space.

Compression stroke

Starting from the suction side of the tooth groove, the meshing of the tooth shape is carried out, and the sealing line gradually moves towards the discharge side, reducing the space of the tooth shape and compressing it.

Compression stroke

By inhaling lubricating oil along with the refrigerant, an oil film seal is formed in the rotor gap, while lubricating the rotor. The positive and negative rotors gradually approach the discharge port for compression, resulting in an increase in pressure.

Discharge stroke

Connect the tooth space to the discharge port and start the discharge stroke. This journey continues until the discharge end, until the refrigerant in the toothed space is completely sent out.

What is piston type air compressor?

When the crankshaft of a piston air compressor / reciprocating air compressor rotates, the piston undergoes reciprocating motion through the transmission of the connecting rod, and the working volume composed of the cylinder inner wall, cylinder head, and piston top surface undergoes periodic changes.

When the piston of a piston compressor starts to move from the cylinder head, the working volume inside the cylinder gradually increases. At this time, gas moves along the intake pipe, pushes open the intake valve, and enters the cylinder until the working volume reaches its maximum, and the intake valve closes; When the piston of a piston compressor moves in the opposite direction, the working volume inside the cylinder decreases and the gas pressure increases.

When the pressure inside the cylinder reaches and is slightly higher than the exhaust pressure, the exhaust valve opens and the gas is discharged from the cylinder until the piston moves to its limit position, and the exhaust valve closes. When the piston of the piston compressor moves in reverse again, the above process repeats.

In short, the crankshaft of a piston compressor rotates once, the piston reciprocates once, and the cylinder undergoes the processes of intake, compression, and exhaust, completing a working cycle.

What is the Difference?

The primary distinction between a screw compressor and a piston (reciprocating) compressor lies in their compression mechanisms. Screw compressors employ two interlocking helical screws, whereas piston air compressors rely on pistons driven by a crankshaft. Additionally, there are notable differences in the number of moving parts between these two types of compressors. Screw compressors have only two moving parts that do not come into contact, whereas piston compressors involve a more complex assembly with multiple moving parts.

Moreover, screw compressors tend to operate at lower temperatures, thanks in part to their efficient cooling systems. These qualities make screw compressors particularly well suited for heavy duty industrial applications.

Another difference is the moving parts as the screw compressor has two moving parts which are not in contact while the piston compressor has a lot of moving parts. The screw compressors operate at a lower temperature and integrate a good cooling system.

Characteristics of air compressor

1. Piston type oil free lubrication air compressor

The piston rings in the cylinder of an oil free air compressor and the packing in the packing device both use self lubricating filled polytetrafluoroethylene as the sealing element. Therefore, the cylinder and packing device do not need to be lubricated with lubricating oil. Under normal circumstances, the compressed gas is basically pure and free of oil stains, and there is no need to add an oil removal device. The disadvantages of this machine are high motor power, unstable exhaust pressure, high exhaust temperature, high noise, heavy maintenance workload, and high maintenance costs.

2. Screw air compressor

The precise coordination between the negative and positive rotors of the screw air compressor, as well as between the rotor and the body shell, reduces gas reflux leakage and improves efficiency; Only the mutual engagement of rotors and the reciprocating motion without cylinders reduce vibration and noise sources. The unique lubrication method has the following advantages: relying on the pressure difference generated by itself, continuously injecting coolant into the compression chamber and bearings, simplifying the complex mechanical structure; Injecting coolant can form a liquid film between the rotors, and the secondary rotor can be directly driven by the main rotor without the need for high precision synchronous gears; The injected coolant can increase the airtightness, reduce the noise generated by high frequency compression, and also absorb a large amount of compression heat. Therefore, even if the single stage compression ratio is as high as 16, the exhaust temperature can not be too high, and there will be no friction between the rotor and the casing due to different thermal expansion coefficients. Therefore, screw air compressors have the advantages of low vibration, no need for anchor bolts to be fixed on the foundation, low motor power, low noise, high efficiency, stable exhaust pressure, and no vulnerable parts. The disadvantage of this machine is that the compressed air contains oil, with an oil content of 1 3 × 10 6. For processes with strict requirements for compressed gas oil content, an oil removal device needs to be added. The compressed air system of the factory has added two stages of oil removal devices. Due to the direct contact between the compressed air in the ADC process and the product ADC foaming agent, there is a higher requirement for air quality. A three level oil removal device has been added to the air used in the ADC process.

ZHEJIANG KITO supplies high cost effective silent air compressor, regarding “ultra quiet “ as destiny optimizing and adjusting the process of production, implementing QC system, and promoting the upgrading and manufacturing of high quality air compressors actively. KITO is looking forward your contact of high pressure belt driven piston type air compressor industrial / building use!