The block member moves from a first position to a second position by contact with {HEAD ~ the slider} sliding in {TAIL ~ a sliding direction} to block and open the air passage 
sliding in
The block member moves from a first position to a second position by contact with { HEAD ~ the slider } sliding in { TAIL ~ a sliding direction } to block and open the air passage
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 TAIL TAIL OTH OTH OTH OTH OTH OTH OTH