Check valve refers to the opening and closing parts for the round valve and rely on their own weight and media pressure to produce action to block the medium backflow of a valve. Is an automatic valve, also known as check valve, check valve, backflow valve or isolation valve. Flap movement is divided into lift and rotary type. Lift check valve and globe valve structure is similar, only the lack of valve stem to drive the valve flap. The medium from the inlet side (lower side) inflow, from the outlet side (upper side) outflow. When the inlet pressure is greater than the weight of the valve and its flow resistance and when the valve is open. Conversely, the valve is closed when the medium flows backwards. Swing check valve has a slant and can rotate around the axis of the valve flap, the working principle is similar to the lift check valve. Check valve is often used as a pumping device of the bottom valve, can prevent the backflow of water. Check valves and globe valves used in combination, can play a safe isolation role. The disadvantage is that the resistance is large and the sealing is poor when closing.