Hattersley check valves (non-return valves) are self-acting devices that allow fluid to flow in one direction and automatically close if flow reverses, protecting systems from backflow. They come in types such as swing, lift, and double check, and are designed for installation in both horizontal and upward vertical piping (though lift types are for horizontal only). Materials include bronze, cast iron, ductile iron, and they are available with different end connections and pressure/temperature ratings depending on application.