Check valve is also called one-way valve or nonreturn valve. Its function is to prevent medium backflow in pipeline. The opening and closing parts are opened or closed by the medium flow and force to prevent the medium backflow. Applied on the pipeline for one-way flow of medium, only allow the medium to flow along one direction to prevent accidents and flow from the inlet side to the outlet side. When the inlet side pressure is lower than the outlet side, the valve disc automatically closes the channel under the action of fluid pressure and its own gravity.