How to choose sewage butterfly valve

Q: Butterfly valve installed in the sewage pipeline, over the sewage, acid alkaline is PH6-8, the temperature is room temperature, should choose what configuration of butterfly valve?

Answer: there is no impurity in sewage, also do not have corrosive stronger material, can use the butterfly valve of ductile cast iron material, butterfly plate USES stainless steel, as for seat, use ternary ethylene propylene rubber can.
 
If the sewage medium contains corrosive, other configuration is unchanged, the seat is made of teflon;
 
The above is only a configuration choice provided according to the working condition mentioned in the problem, for reference only.