casting a flexible membrane into a first membrane through hole of the second rigid layer such that the flexible membrane has {TAIL ~ a passageway surface} that is adapted to be either substantially coplanar to {HEAD ~ the second surface} of the first rigid layer when the valve is in an open position, or bulged with a central portion thereof being substantially coplanar to the plateau surface of the valve seat when the valve is in a closed position 
casting a flexible membrane into a first membrane through hole of the second rigid layer such that the flexible membrane has { TAIL ~ a passageway surface } that is adapted to be either substantially coplanar to { HEAD ~ the second surface } of the first rigid layer when the valve is in an open position , or bulged with a central portion thereof being substantially coplanar to the plateau surface of the valve seat when the valve is in a closed position
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD 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