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