Below is a list of Stainless Steel Butterfly Valves manufacturers from King of Prussia, Pennsylvania. Stainless steel butterfly valves are devices that regulate the flow of various liquids and gases in pipes. Butterfly valves are rotary valves, meaning their disc rotates a quarter turn between the open and closed positions. Like all butterfly valves, stainless steel butterfly valves consist of a seal around a pipe wall, a round disc or plate and a control lever.