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