Rotary screw air compressors are equipped with two spindle shaped mutually engaging rotors. As a rule, the main rotor is made with four, the auxiliary rotor with six lobes, where the main rotor transforms about 85-90% of the energy received at the coupling from the drive motor into pressure and heat energy. Injection technology led to the development of the rotary screw air compressor without synchronous transmission but with oil injection cooling, where the rotors could counter rotate in a non-contacting manner because of the lubrication provided by the injected oil.