This is of a dried out vacuum pump is a pump that does not use any fluids to create a vacuum or contact the process gas and can also discharge to atmosphere. … Timing gears with essential oil reservoirs and close clearances between your rotors 
Principle of Dry Vacuum Pump Operation
Dry screw vacuum pumps operate with two screw rotors rotating in reverse directions. This traps the moderate to become pumped between the cylinder and the screw chambers and transports it to the gas discharge. … It also results in a lesser temperature load of the compressed gas.