US Patent 6883518 Unidirectional respirator valve

A unidirectional valve, wherein the valve comprises a valve body including a frame, a valve opening through the frame, and a valve seat extending from the frame and at least partially surrounding the valve opening. The valve further includes a valve flap having a first portion attached to the frame and an adjacent second portion free to move from a first position where the second portion is in contact with at least a part of the valve seat to a second position where at least part of the second portion is spaced from the valve seat, wherein the valve flap has a nonuniform thickness. The thickness variations may occur between sides of the valve flap, and may also occur between the ends of the valve flap.