Tozen automatic air vent most widely used type of air valve and characterized by small orifices, weighted float and leverage mechanism. Combination of these features allow air vent to expel air or gas at full operating pressure. Tozen air vent divide into two type which are CAAV-B for PN 16 and DAAV-B25 for PN 25. Both threaded to BS 21(ISO 7) / ASME B1 20.1