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