The present disclosure is directed to a combination air valve that uses buoyancy to lift seals into place, preventing media from escaping from the valve. Once the seals are in place, pipeline pressure is used to open and close the valve. The combination air valve includes a piston assembly which includes a main disc, a piston head located above the main disc, a float below the main disc, and a float shaft joining the float to the piston. When no media is in the valve the float is at the bottom of the valve and the main disc is down, allowing gases to leave the valve. The float is lifted as media enters the valve, thus using buoyancy to lift the main disc into place, preventing media from escaping from the valve. Once the seals are in place, pipeline pressure is used to open and close the valve.