A check valve refers to a type of valve whose opening and closing components are circular valve discs that act by their own weight and medium pressure to block medium backflow. It belongs to the category of automatic valves, also known as check valves, one-way valves, return valves or isolation valves. The valve disc movement can be divided into lifting and rotating types. Lift check valves have a similar structure to globe valves, except for the lack of a valve stem that drives the valve disc. The medium flows from the inlet end (the rotary check valve has a valve disc that is inclined and can rotate around the axis, and its working principle is similar to that of a lift check valve. The check valve is commonly used as the bottom valve of a pumping device to prevent water from flowing back. When used in combination with a globe valve, the check valve can provide safe isolation. The disadvantage is high resistance and poor sealing when closed.