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