When the diaphragm is in a sealing position, in contact with the valve seat and seated upon the generally flat surface, the edges of the diaphragm overlap {HEAD ~ the surface} of {TAIL ~ the dome} that slopes away, but are not resting against it 
When the diaphragm is in a sealing position , in contact with the valve seat and seated upon the generally flat surface , the edges of the diaphragm overlap { HEAD ~ the surface } of { TAIL ~ the dome } that slopes away , but are not resting against it
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH 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