The oil-free screw compressor element
No oil implies that there is no essential oil for sealing the rotors and for cooling the compressed air, components and rotors. … The component 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 comes 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 due to internal conditions.