Embodiments of the invention include a unidirectional exhalation valve for a respiratory device such as a facemask. The valve opens to vent air out of the interior of the facemask and closes to prevent the inflow of ambient air. The valve is comprised of a valve body, a valve cover and a membrane. The membrane is secured to the valve body around its perimeter by the valve cover. The membrane is comprised of two or more flaps that flex toward a central region, in a direction away from the valve body, to open the unidirectional valve.本發明之實施例包括用於諸如面罩之呼吸裝置的單向呼氣閥。前述閥打開以將空氣放出於面罩之內部外，且關閉以防止環境空氣的流入。前述閥由閥體、閥蓋及膜構成。前述膜藉由前述閥蓋圍繞其周邊緊固至前述閥體。前述膜由兩個或更多個瓣構成，前述兩個或更多個瓣在遠離前述閥體之方向上朝向中央區撓曲以打開前述單向閥。
