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Check valve is to prevent the line of medium back. Pump water off the end of the valve check valve class also belong. Opening and closing pieces by medium flow and the forces to open or close the valve to prevent the media called back check valve. Check valves are automatic valves, mainly for one-way flow of media channels, only allowing media to flow in one direction, to prevent accidents. Check valve according to the structure are divided into lift check valve, swing check valve and butterfly valve of three. Lift check valve can be divided into two kinds of vertical and horizontal. Swing check valve into unicuspid type, double disc type and the multi-jaw type of three. Butterfly valve for the straight-through, more than some form of check valve in the connection can be divided into the threaded connection, flange connection and welding of three. Check valve should be aware of the following things to install the top: 1 Do not check valve in the pipeline to withstand the weight of a large check valve should be independent of support, so that the pressure piping system from the impact. 2, installation, pay attention to the direction of media flow valve by the votes should be consistent with the direction the arrow. 3, vertical valve lift check valve should be installed in the vertical pipe. 4, the level of valve lift check valve should be installed in horizontal pipelines.