Water-injected Oil-free VS Dry Oil-free Screw Air Compressor

For the Dry oil-free screw air compressor, most are twin-screw air compressors. Water-lubricated oil-free screw air compressor is also called a water-injected screw air compressor, most are single screw air compressors. The following analyze their differences:

COMPARISONS

Water-injected Oil-free Single Screw Air Compressor	VS	Dry Oil-free Double Screw Air Compressor
Working Principle
Comparison	Water-lubricated Oil-free Single Screw	Dry Oil-free Double Screw
Air Quality	100% Oil-Free	Oil in the gear
Air Purity	Clear air after purified by water	Contain dust and oil stain
Lubrication Media	Pure Water	Dry
Air Temp	Less than 55℃	About 180~200℃
Compression	Single-Stage	Two-stage
Cooling method	Don’t need a cooling system	Need interstage and after Cooling system
Structure	Simple and Balanced Structure	Radial load is not balance
Vibration and Noise	Low vibration and noise	High-frequency noise due to the two screws
Durability	Ideal Rotation speed 3000r/min, theoretically zero loads.   Long lifetime of the screw (30000h) and star wheel (50000h)	Rotation speed 18000r/min, high loads on screws.   The short lifetime of the screw (8000~18000h)
Maintenance	Only air and water filter elements	More spare parts

Different principles

1. The dry oil-free screw air compressor means that the coating on the surface of the rotor teeth will play the role of lubrication and sealing. There is no lubrication medium in the compression chamber. But there is lubricating oil in the gearbox;
2. But for the Water-lubricated oil-free type means that the water and air are mixed and compressed. Water plays the role of lubricating, sealing, cooling, and denoising

Different Prices

1. Water-lubricated oil-free type is mostly single-screw air compressors. The price is generally lower than the dry oil-free type. The maintenance cost is also lower. Only air filter elements and water filter elements.
2. But for the dry oil-free air compressor, except for the spare parts, the coating also needs to be replaced regularly.

Different Losses

1. Water-injected oil-free single screw type: ideal isothermal compression, no heat loss.
2. Dry oil-free double screw type: energy lost due to hot air discharge