Safe return valve working principle and structure: safety valve in the system from the safety protection. 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. For the ball valve and diaphragm safety valve, working principle and piston exactly the same. These three safety valves are spring to provide control, adjust the spring preload, you can change the safety value of the size, so called direct acting safety valve. For the pilot-operated safety valve, with a small direct acting valve to provide control of the pressure acting on the diaphragm, the diaphragm is the core of the hard core, pressure on the seat. When the air pressure A greater than the safety pressure, the spool open, compressed air from the left output hole into the atmosphere. Diaphragm-type safety valve and pilot-operated safety valve pressure characteristics better, sensitive action; but the maximum opening force is relatively small, that is, poor flow characteristics. Practical application, should be based on the actual need to choose the type of safety valve, and according to the maximum displacement of its choice of path. 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. Safety return valve spring and rod two categories. 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, lever safety valve rely mainly on the leverage of the hammer work, but the large size of the lever safety valve often limits the choice of range. When the temperature is high, select the safety valve with a radiator. When the anti-reflux valve installed only in emergency situations, usually rarely used water lines, such as fire sprinkler pipelines, do not install the filter. The reason for this may be that (1) the first check valve is contaminated, and (2) the pressure at the inlet of the unit drops too much due to upstream pressure fluctuations. In addition, this safety valve may be released (splashed) if the second check valve is contaminated during an emergency backwash or water hammer.