The oil-free screw compressor element
No oil implies that there is absolutely no essential oil for sealing the rotors and for cooling the compressed air flow, elements and 
rotors. … The element is usually cooled by cooling drinking water that flows through special Oil-free Screw Air Compressor pockets in the component casing.
In a lubricated screw compressor, the lubricant will come in direct in contact with the compressor inlet air and compressed air. … The oil contains anti-oxidants to attempt to reduce the breakdown of the lubrication properties due to internal conditions.