Check valves are valves that use a circular valve disc to block reverse flow of medium by relying on their own weight and medium pressure to operate. They belong to the category of automatic valves and are also known as non-return valves.One-way valveCheck valves or isolation valves. The movement methods of the valve discs are divided into lifting and tilting types. The lifting type check valve has a structure similar to that of a stop valve, but lacks the valve rod that drives the valve disc. The medium flows into the inlet (lower side) and out of the outlet (upper side). When the inlet pressure exceeds the sum of the valve disc's weight and its flow resistance, the valve opens. Conversely, when the medium reverses flow, the valve closes. The tilting type check valve has a valve disc that is obliquely positioned and can rotate around an axis, with a working principle similar to that of the lifting type check valve. Check valves are commonly used as bottom valves in pumping units to prevent backflow of water. When combined with stop valves, they can serve as a safety isolation. The drawback is that they have high resistance and poor sealing when closing.