The undersurface of the top portion 21 of the valve member 20 forms {HEAD ~ another sealing surface} 40 for selectively substantially preventing {TAIL ~ fluid flow} through the opening 28 
for selectively substantially preventing
The undersurface of the top portion 21 of the valve member 20 forms { HEAD ~ another sealing surface } 40 for selectively substantially preventing { TAIL ~ fluid flow } through the opening 28
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH