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