Safety valve safety valve in the system play a security role. When the system pressure exceeds the set value, the safety valve Ting open, part of the system in the gas into the atmosphere, the system pressure does not exceed the allowable value, thus ensuring the system is not an accident due to excessive pressure. Safety valve, also known as relief. Icon for the safety valve of several typical structure. Figure A is a piston valve, the valve core is flat. Air pressure in the piston A, when the pressure exceeds the spring force to determine the safety value, the piston A is the top open, part of the compressed air that is discharged into the atmosphere from the valve port; when air pressure falls below the safety value, spring-driven piston down, close the valve port.