reference can be made for example to japanese patent no 2691168 japanese unexamined patent publication kokai no 2 70990 a reversed flow cooled 3 stage roots type vacuum pump having a first a second and a third pump sections 401 402 and 403 is shown in fig4 the v u2014 v section of fig4 is shown in fig5 and vi u2014 vi section in fig6 the first pump section 401 and the second pump section 402 is partitioned by a wall 404 and the second pump section 402 and the third pump section 403 is partitioned by a wall 405 the first shaft 406 and the second shaft 407 are supported by two bearings 408 and are rotated in opposite directions by timing gear set 409 the first shaft 406 can be driven by a motor each of the pump sections is constituted by a housing 412 and rotors 413 a 413 b supported by a pair of shafts 406 407 around the circumference of the housing 412 there are circumferential gas passages 414 a and 414 b communicating the discharge outlet 414 and the inlets 415 a and 415 b for guiding the gas for the reversed flow cooling into the housing and directing it to the next stage pump section in the circumference of the circumferential gas paths 414 a 414 b there is a cooling water passage 416 in the vacuum pump of fig4 the suction gas g 0 is drawn into the housing 412 through the suction inlet 410 of each pump section and is conveyed.