1) Air valves shall be of the elongated body type and shall have a pressure rating of 3 bars unless otherwise stated in the Contract.(2) Dual orifice air valves shall have:(a) A small orifice valve for releasing air at working pressure, and(b) A large orifice valve for allowing air to pass at atmospheric pressure during emptying and filling of pipework.(4) Small orifice valves shall have an adjustable Vitron orifice button to ensure positive sealing. Large orifice valves shall have a Buna-N seat.(5) The valve inlet of small orifice valves shall be 75 mm diameter and the valve outlet shall be 25 mm diameter. The venting orifice shall be 5 mm diameter. The valve inlet and the valve outlet of large orifice valves shall be 75 mm diameter.(6) Air valves shall be provided with isolating gate valves.