Vacuum pump

Abstract

A vacuum pump ( 10 ) includes a pump casing ( 56 ) having an inlet port ( 54 a ), an outlet port ( 54 b ), and pump chambers ( 50 a - 50 f ) defined therein, rotational shafts 60 having opposite ends rotatably supported by bearings ( 84 a, 84 b ) on the pump casing ( 56 ) and extending longitudinally in the pump casing ( 56 ), and rotors ( 62 a - 62 f ) housed in the pump chambers ( 50 a - 50 f ) and coupled to the rotational shafts ( 60 ) for rotation in unison with the rotational shafts ( 60 ). The pump casing ( 56 ) has an atmosphere-vented compartment ( 52 ) defined therein which is held in fluid communication with the outlet port ( 54 b ) of the pump casing ( 56 ) and vented to the atmosphere.

1 . A vacuum pump comprising:
 a pump casing having an inlet port, an outlet port, and a pump chamber defined therein;   a rotational shaft having opposite ends rotatably supported by bearings and extending longitudinally in the pump casing; and   a rotor housed in the pump chamber and coupled to the rotational shaft for rotation in unison with the rotational shaft;   wherein the pump casing has an atmosphere-vented compartment defined therein which is held in fluid communication with the outlet port of the pump casing and vented to the atmosphere.   
     
     
         2 . A vacuum pump according to  claim 1 , wherein the pump chamber comprises a plurality of pump chambers held in fluid communication with each other, and the rotor comprises a plurality of rotors disposed respectively in the pump chambers for rotation in unison with the rotational shaft. 
     
     
         3 . A vacuum pump according to  claim 1 , further comprising:
 a side panel disposed on an end wall of the pump casing, the rotational shaft extending through the side panel, the side panel having a purge gas passage defined therein for supplying a purge gas to a portion of the rotational shaft which is disposed in the side panel.   
     
     
         4 . A vacuum pump according to  claim 2 , further comprising:
 a side panel disposed on an end wall of the pump casing, the rotational shaft extending through the side panel, the side panel having a purge gas passage defined therein for supplying a purge gas to a portion of the rotational shaft which is disposed in the side panel.