Safety valve used in pressure equipment, containers or pipe on the road, as the overpressure protection device. When the equipment, containers or increased pressure inside the pipe more than the allowable values, the safety valve automatically opens, and then the entire amount of emissions in order to prevent equipment, container or piping inside the pressure continues to rise; when the pressure reduced to the provisions of the value of , the safety valve of the valve should be automatically shut down in time to protect equipment, containers or the safe operation of pipelines. Safety valve can be imported by the system pressure valve direct-drive, in this case is provided by a spring or weight to overcome the role of mechanical load in the valve below the medium pressure valve. Can also be from an agency to drive the pilot, the agency or through the release of the closure imposed by force in order to make a safety valve to open or closed. Therefore, in accordance with the drive mode can be divided into the direct effect of a safety valve and pilot-style. Safety valve can be opened in the high range or open to a large proportion of highly open framework, it may be only a tiny opening in the framework of a high proportion of open, and then suddenly open to a wide-open position. Therefore, it can be divided into the safety valve and the proportion of full-Kai style.