Answer to Question #234170 in Civil and Environmental Engineering for Janu

Question #234170

11. Nowadays, most flap valves are made of HDPE. What are the advantages of using HDPE when compared with cast iron?

Expert's answer


  • It has no reaction with sewage and seawater and does not suffer from the corrosion problem associated with cast iron.
  • No protective coating is required and it is almost maintenance-free.
  • HDPE flap valves require very low opening pressure in operation (like 5mm water level difference). For cast iron flap valves, due to its own heavy self-weight, the required opening pressure of cast iron flap valves is higher than that of HDPE flap valves. This criterion is essential for dry weather flow conditions.

However, the pressure resistance of HDPE flap valves is not as good as cast iron flap valves. For instance, a typical 450 mm wide HDPE flap valve can only withstand about 5 m water column.

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