a plurality of air inlets 32 at {TAIL ~ the lower periphery} of {HEAD ~ the inner tube} 30, and 
a plurality of air inlets 32 at { TAIL ~ the lower periphery } of { HEAD ~ the inner tube } 30 , and
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH