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 {HEAD ~ a sealing edge} 
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 { HEAD ~ a sealing edge }
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD