a discharge part that discharges the gas sucked by the suction part, the discharge part having {HEAD ~ a plurality} of rotating {TAIL ~ impellers} and a stationary impeller arranged so as to be opposed to each of the plurality of rotating impellers; and 
of rotating
a discharge part that discharges the gas sucked by the suction part , the discharge part having { HEAD ~ a plurality } of rotating { TAIL ~ impellers } and a stationary impeller arranged so as to be opposed to each of the plurality of rotating impellers ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH