The oil-free screw compressor element
No oil means that there is no oil for sealing 
the rotors and for cooling the compressed surroundings, elements and rotors. … The component can be cooled by cooling water that flows through unique pockets in the component casing.
In a lubricated screw compressor, the lubricant comes in direct in touch with the compressor inlet air and compressed air. … The oil contains anti-oxidants to attempt to reduce the break down of the lubrication properties due to Oil-free Screw Air Compressor china internal conditions.