The valve combines small and large orifices. It consists of a specially designed single small orifice valve and a single large orifice valve, with modified bodies to allow bolting together and free flow between them. The small orifice valve comprises a Stainless Steel float with polymer guide and rolling seal mechanism to seal the small orifice vent. When the large orifice float chamber is filling with water, the orifice is closed initially by the float. When the large orifice chamber is filled with water under pressure, the orifice is held closed by the combined up thrust of the float and the differential pressure over the orifice area. On air accumulated in the system entering the chamber under working pressure, the water level in the small orifice chamber is depressed until it reaches a point when the weight of the float is sufficient to uncover the orifice and exhaust air. Air is expelled until the water level rises again in the small orifice chamber and causes the float to close the orifice. The large orifice valve consists of a sealing off a large orifice vent to the atmosphere. The float is held at a predetermined height in its casing by specially designed cage which also guides the float onto the seat. During pipeline filling or emptying, the Aerodynamic feature holds the float off the seat and keeps it completely stable under all air outflow or inflow conditions. The valve cannot close prematurely during outflow. It closes only when water enters the casing and raises the float onto the seat.