SWING CHECK VALVES: A basic swing check valve consists of a valve body, a bonnet, and a disk that is connected to a hinge. The disk swings away from the valve-seat to allow flow in the forward direction, and returns to valve-seat when upstream flow is stopped, to prevent backflow. The disc in a swing type check valve is unguided as it fully opens or closes. There are many disk and seat designs available, in order to meet the requirements of different applications. The valve allows full, unobstructed flow and automatically closes as pressure decreases. These valves are fully closed when flow reaches zero, in order to prevent backflow. Turbulence and pressure drop in the swing check valve are very low.