A check valve is a valve in which the opening and closing parts are circular disc and act to block the backflow of the medium by means of their own weight and dielectric pressure. It is an automatic valve class, also known as an inverse valve, a check-valve, a reflux valve or a isolation valve. Disc motion mode is divided into lifting type and swivel type. The lifting check valve is similar to the cut-off valve structure and only lacks the stem that drives the disc. The medium flows from the inlet (lower side) and flows out of the outlet (upper side). When the inlet pressure is greater than the disc weight and the sum of its flowing resistance, the valve is opened. Conversely, the valve shuts down when the media is reversed. The swivel check valve has a disc that is oblique and rotates around the shaft and works in a similar working principle to the lifting check valve. The check valve is often used as the bottom valve of the pumping device, which can prevent the reflux of water. The fastening valve is used in combination with the globe valve, which can play the role of safety isolation. The disadvantage is high resistance, poor sealing when shutting down.
