Check valves are valves that use a circular valve disk and rely on their own weight and medium pressure to prevent backflow of the medium. They belong to the category of automatic valves and are also known as non-return valves, one-way valves, return valves, or isolation valves. The motion of the valve disk is divided into lifting and tilting types. The lifting type check valve has a structure similar to a stop valve, but lacks the valve rod that moves the disk. The medium flows into the inlet (lower side) and out of the outlet (upper side). When the inlet pressure exceeds the sum of the disk weight and its flow resistance, the valve opens. Conversely, when the medium backflows, the valve closes. The tilting type check valve has a tilted disk that can rotate around an axis, with a working principle similar to the lifting type. Check valves are commonly used as bottom valves in pumping equipment to prevent water backflow. When used in combination with stop valves, they can serve as a safety isolation. The disadvantages include high resistance and poor sealing when closing.