This design of air valve for use in water systems incorporated both small and large orifices. The small orifice for automatic release of accumulated air during normal operation. The large orifice allows automatic ventilation of the pipeline during filling and emptying. When filling, air is exhausted at a sufficiently high capacity to prevent restriction of the filling rate due to built up back pressure. When emptying, air is admitted to the pipeline at a rate sufficient to prevent high vacuum pressures developing.
