Safety valve in the system play a safety role. When the system pressure exceeds the specified value, the safety valve Ting open, the system part of the gas into the atmosphere, the system pressure does not exceed the allowable value, so as to ensure that the system is not over pressure and accidents. Safety valve, also known as relief valve. Piston safety valve, spool is a flat. When the pressure exceeds the safety value determined by the spring force, the piston A is pushed open and part of the compressed air is discharged into the atmosphere from the valve port. When the pressure of the air source is lower than the safety value, the spring is driven Pistons down, close the valve port. A valve that protects the system from being over-pressurized can automatically relieve pressure once the medium pressure in the system line or device exceeds the set value, thus achieving the goal of safety protection. There are also impulse-type safety valve, pilot-operated safety valve, safety switch valve, safety relief valve, static heavy-duty safety valve. Spring-loaded safety valve depends mainly on the force of the spring to work, spring-loaded safety valve has closed and not closed, the general flammable, explosive or toxic media should be used closed, steam or inert gas can choose not closed Type, in the spring-loaded safety valve with wrench and without wrench. The role of the wrench is to check the valve flap flexibility, and sometimes can also be used as a manual emergency relief pressure, as shown in Figure 3. Lever safety valve rely mainly on the leverage of the hammer and work, but because of the large size of the lever safety valve often limits the scope of selection. When the temperature is high, select the safety valve with a radiator. The main parameters of the safety valve is the displacement, the displacement depends on the caliber of the valve seat and the valve opening height, the opening height is different, is divided into two kinds of micro-Kai and full Kai. Micro-Kai refers to the valve opening height of the valve seat throat diameter 1/40 ~ l / 20. Throttle refers to the valve opening height of the valve seat throat diameter 1/4.