Oil-free screw air compressor
The first twin-screw air compressor had symmetrical rotor profiles and did not use any coolant in the compression chamber. These are known as oil-free or dry screw air compressors. The asymmetric screw configuration of the oil-free screw air compressor greatly improves energy efficiency because it reduces internal leakage. External gears are the most common device for synchronizing rotors in reverse rotation. Since the rotors cannot come into contact with each other or the housing, lubrication is not required in the compression chamber. Therefore, the compressed air is completely oil-free. The rotor and casing are precisely manufactured to minimize leakage from the compression point to the intake. The built-in compression ratio is limited by the ultimate pressure difference between the intake and exhaust ports. This is why oil-free screw air compressors generally have staged compression and built-in cooling to achieve higher pressures.
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Schematic diagram of twin-screw compression
Typical air end and motor of oil lubricated screw air compressor air end
Oil-injected screw air compressor with motor
The head of an oil-free screw air compressor has a liquid-cooled rotor shell, air seals and oil seals at both ends, and a set of synchronization gears to maintain a small gap between the rotors.
Liquid injection screw air compressor
In a liquid screw air compressor, the liquid enters the compression chamber and often enters the air compressor bearings. Its function is to cool and lubricate the moving parts of the air compressor, cool the air compressed inside, and reduce leakage back into the intake duct. Nowadays, lubricating oil is the most common injection liquid because of its good lubricity and sealing properties. At the same time, other liquids such as water or polymers are also often used as injection liquids. Liquid-injected screw air compressor components can be applied to high compression ratios. One-stage compression is usually sufficient and can increase the pressure to 14bar or even 17 bar, although the energy efficiency will be reduced.
Oil-injected screw air compressor flow chart
Oil-free screw air compressor flow chart
Post time: Nov-03-2023
