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