Designing a potable water tank farm and I'm trying to determine whether or not the gate valve I want to use are acceptable. Typically I design B31.3, 31.4, and 31.8 piping systems so potable water design is foreign to me.
I know NSF 61 and AWWA have material requirements for valvesWRC ( Water Research Council UK ) approved valves, materials &  coatings are a good place to start to determine the correct selection of valves for potable water.
Typically, 316 stainless steel and certain types of copper alloys are acceptable, along with UPVC and ABS plastics.
Cast iron bodied valves are acceptable with the correct internal epoxy coating. Seal materials such as EPDM rubber have to be individually approved and certified by an approval body such as the WRC to ensure that the particular 'recipe' for that elastomer is acceptable. Virgin PTFE is generally accepted as inherently acceptable. But it really depends in which country you plan to build the plant, as most have the own local by-laws governing materials for potable water .

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