Check valve is a kind of valve whose opening and closing parts are round disc and whose action is produced by its own weight and medium pressure to block medium reverse flow. Automatic valve class, also known as the check valve, one-way valve, backflow valve or isolation valve. Disc movement is divided into lifting type and swing type. Lift-type check valves are similar to globe valves except for the absence of a stem to drive the disc. The medium flows in from the inlet end (lower side) and out from the outlet end (upper side). The valve is opened when the inlet pressure is greater than the combined weight of the disc and its flow resistance. Conversely, the media flow back when the valve is closed. Swing check valves have a tilted disc that rotates about the shaft and work in a similar manner to lift check valves. Check valves are commonly used as bottom valves in pumping units to prevent backflow of water. The combination of stop valve and globe valve can play the role of safety isolation. Disadvantages are high resistance, poor sealing when closed.