Boiler safety valve

A boiler safety valve is a spring-loaded pressure-relief valve that opens automatically to vent steam when boiler pressure reaches the set point, preventing overpressure of the drum and shell. It is sized and certified to ASME Boiler and Pressure Vessel Code Section I or the equivalent classification-society rules, with the combined relieving capacity at least equal to the boiler maximum continuous evaporation so pressure cannot rise more than 10% above the maximum allowable working pressure. Auxiliary and exhaust-gas boilers each carry at least two valves, set with a small differential so they lift in sequence.