The 
oil-free screw Oil-free Screw Air Compressor compressor element
No oil implies that there is no essential oil for sealing the rotors and for cooling the compressed air, elements and rotors. … The element is definitely cooled by cooling drinking water that flows through special pockets in the element casing.
In a lubricated screw compressor, the lubricant comes 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.