Installation for strict to prevent the media back, followed by the media or equipment to protect against contamination of non-return type valve in the piping system of various types. By two check valves and a transition portion composed of a series, sealed tight, make sure the media without a little reflux. Pipeline anti-fouling off valve is used to prevent the occurrence of drinking water pipeline pollution by backflow safety device to ensure the health and safety of drinking water. Product structure: safe anti-fouling off valve is between the two check valves plus a drainage components. Chamber with high-pressure hose connected to the inlet end level check drainage. First, the two check valves is mainly composed of body, valve cover, valve, gaskets, springs and other components. Drainage is mainly made up of body, bonnet, diaphragm, valve, seal plate, valve, valve seats, springs and other components. Ordinary anti-fouling off valve for the two check valves in series. How it works: anti-fouling off valve for the two check valves in series, which has a seal when the destruction, the other also acts as a seal to prevent backflow. But after only two valve seals at the same time destroy, they lost only back role, its safety and reliability of relatively badly, the working principle is simple. Middle drainage, so even if the two valve seals while only damage, which may also play a role to prevent backflow contamination anti-fouling off valve on the basis of the ordinary type.