casting a flexible membrane into a first membrane through hole of the second rigid layer such that the flexible membrane has a passageway surface that is adapted to be either substantially coplanar to 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 {HEAD ~ the plateau surface} of {TAIL ~ 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 a passageway surface that is adapted to be either substantially coplanar to 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 { HEAD ~ the plateau surface } of { TAIL ~ the valve seat } when the valve is in a closed position
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