(i) It has no reaction with sewage and seawater and does not suffer from the corrosion problem associated with cast iron.
(ii) No protective coating is required and it is almost maintenance-free.
(iii) 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 450mm wide HDPE flap valve can only withstand about 5m water column.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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