Abstract: A quick-action valve is opened and closed by a quarter turn. Safe closing with high mechanical advantage is provided, while the valve member is removed completely from the path of the flow upon valve opening. The valve member is fixed to a valve arm, mounted for rotation on a shaft. The valve includes an auxiliary shaft around which an actuating arm with a roller fixed to it are turnable. The roller moves the valve arm, or an auxiliary arm connected to it, so that upon closing it rolls substantially tangentially on a camming surface, thus bringing about maximum force transmission. A few degrees after the dead center position, rotation of the actuating arm is limited by a stop, and self-holding takes place in the closed position. In a preferred version the roller runs in the groove on the valve arm or auxiliary arm.