The apparatus 4 wherein said opening is the open bottom end of said cylindrical casing and said element is circular and substantially concentric with said cylinder and wherein said diaphragm when subjected to pressure head balloons upwardly in an annulus in the space between the inner wall of {HEAD ~ said cylinder} and the edge of {TAIL ~ said element} 
The apparatus 4 wherein said opening is the open bottom end of said cylindrical casing and said element is circular and substantially concentric with said cylinder and wherein said diaphragm when subjected to pressure head balloons upwardly in an annulus in the space between the inner wall of { HEAD ~ said cylinder } and the edge of { TAIL ~ said element }
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 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 OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL