What's the difference between boiler safety valve and pressure limiting valve?

Safety valve is an over-pressure protection device of boiler. When the pressure reaches a certain value, the safety valve acts to discharge excess steam, quickly reduce the pressure and prevent overpressure explosion accidents. The safety valve is equivalent to a switch, which acts instantly. The pressure limiting valve continuously adjusts the steam flow to control the steam pressure, which is equivalent to an analog signal. Safety valves usually release excess steam into the atmosphere, while pressure limiting valves do not.