The pressure of the back pressure valve is achieved by the spring force of the built-in spring. When the system pressure is smaller than the set pressure, the diaphragm clogs the pipe under the action of the spring force. When the system pressure is larger than the set pressure, the diaphragm compresses the spring, Connected to the liquid through the back pressure valve. In the pipeline or equipment container pressure instability, the back pressure valve to maintain the required pressure pipeline, so that the pump can output the normal flow. Also at the end of the pump due to gravity or other effects often appear siphon phenomenon, this time the back pressure valve can reduce the siphon caused by the flow and pressure fluctuations. And for metering pumps and other volumetric pumps at low system pressure to work, there will be excessive transport. In order to prevent similar problems, the metering pump must be imported and exported at least 0.7Bar back pressure, generally through the metering pump outlet to install the back pressure valve to achieve the purpose.