I'm designing a potable water tank farm and I'm trying to determine whether or not the 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 valves. What other codes and standards cover valves for potable water service? 

WRC ( 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.

Jeffvalve has a good description of your choices, most important (as also illustrated by stanier) is your localization.

Commercially there is a fierce competition among producers and suppliers to this type of application, and prices and quality will vary, as well as troublefree standtime.

Preferred types of valves, and brands will vary according to sizes, pressures, local regulations and local competition. (Give more data and get more directadvice regarding brands and types)

You may well use cast iron or nodular cast iron valves, properly coated with approved coating and sealings in SS pipelines. I would strongly recommend price/lifetime comparisons before choice anyway.

Selection between gatevalves and butterflyvalves will depend on size and pressure class.

If butterflyvalves are selected, double eccentric valves should be compared to centric on price/troublefree lifetime basis.

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