The oil-free screw compressor element
No oil means that there is no oil for sealing the rotors and for Oil-free Screw Air Compressor cooling the compressed atmosphere, elements and rotors. … The element is usually cooled by cooling drinking water that flows through unique pockets in the element 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 breakdown of the lubrication properties due to internal conditions.