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