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