Therefore, the surface of the dome that slopes away, all around {TAIL ~ the perimeter} of {HEAD ~ the valve seat}, is the non engaging surface referred to above 
Therefore , the surface of the dome that slopes away , all around { TAIL ~ the perimeter } of { HEAD ~ the valve seat } , is the non engaging surface referred to above
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH