The relief valve is pressure equipment (such as containers, pipes) on the overpressure protection device. When pressure equipment to the expected value, the relief valve automatically open pressure, prevent equipment pressure continued to rise. When pressure is reduced to the specified value, the safety valve automatically shut off in time, prevent the loss of equipment within the medium. Under external force of the relief valve opening and closing parts in a normally closed state, when the equipment or piping within the medium pressure than specified value, through a discharge medium system to prevent the pipeline or equipment within the medium pressure in excess of the prescribed value. Relief valve belong to automatic valve class, mainly for the boiler, pressure vessel and piping, control pressure shall not exceed the specified value, to protect personal safety and equipment operation plays an important role.