The DT-040 combination air valve is designed to prevent problems caused by presence or absence of air in small water supply systems. The combination air valve combines an air & vacuum large orifice and an automatic small orifice in one single body. It is the outcome of development, based on many years of experience, resulting in the production of this revolutionary valve. The combination air valve discharges air during the filling of the system and admits air while draining. It also releases accumulated air from the system while the system is operating under pressure.