The oil-free screw compressor element
No oil implies that there is absolutely no oil for sealing the rotors and for cooling the compressed atmosphere, elements and rotors. … The element is Oil-free Screw Air Compressor certainly cooled by cooling drinking water that flows through special pockets in the component casing.
In a lubricated screw compressor, the lubricant will come 
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 because of internal conditions.