Both rotors fit precisely into each other and release only little space between their wings and to the case. Thus they operate with the greatest possible efficiency. They are twisted helical to hold the pressure fluctuations as small as possible. With revs up to 10,000 1/min they can be operated with usual roller bearings.
How to recognize a defect? Since there is a noise when powerful accelerating that detected early enough, originates from the slight coincidence of the two rotors or a rotor with the wall. Without countermeasures, ie the replacement of the compressor, it can easily lead to total loss. The blocking of the two rotors is even harmless. But woe, metal parts splinter and get into the engine. 11/12