{HEAD ~ The annular protrusion} is symmetrical about the orifice and has a proximal end affixed to the valve body with {TAIL ~ an inwardly directed extension} which provides a sealing edge 
{ HEAD ~ The annular protrusion } is symmetrical about the orifice and has a proximal end affixed to the valve body with { TAIL ~ an inwardly directed extension } which provides a sealing edge
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH