An evacuating apparatus includes a first pump section disposed on a suction opening side, a second pump section for exhausting a smaller amount of gas than the first pump section, the second pump being disposed in an exhaust opening side, a plurality of rotors accommodated in a housing, bearings for...http://www.google.co.uk/patents/US5564907?utm_source=gb-gplus-sharePatent US5564907 - Evacuating apparatus
