Thus, {HEAD ~ this valve mechanism} can open and close {TAIL ~ the air communication portion} in a reversible manner 
close
Thus , { HEAD ~ this valve mechanism } can open and close { TAIL ~ the air communication portion } in a reversible manner
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH