A42 spring full open safety valve is applicable to equipment and pipelines with air ≤300°C and other non flammable, explosive, non corrosive gas and other media. When the media pressure reaches the specified opening pressure, the valve automatically opens (the opening height is not less than 1/4do), and then discharges in full. When the pressure drops to the specified reseating pressure, the valve automatically closes to ensure the safe operation of equipment and pipelines.