... can normally 3 meters in the underwater work, but this height is, counting from the bottom of the duckbill check valve, plus ... Duckbill Check Valve Advantage:1) Based on the difference in water pressure automatically turn on and off, safe and reliable, ... Reverse backstop seal, no leakage, prevent backflow, the greater the back pressure, the better the effect. 4) Anti-corrosion, adaptability, and long ...