The check valve is a type of automatic valve that uses the force of the medium to open and close disc, preventing backflow of the medium. When a fluorine lining is applied to the flow surface of the check valve, it isolates the medium from direct contact with the metal body. This type of valve is known as a fluorine-lined check valve. It automatically opens when corrosive media flow in the forward direction and closes against the flow , effectively preventing backflow. T