5.11.3(c) Valve trim. Stems, discs or disc faces, seats and other wearing parts of valves are to be of corrosion resistant materials suitable for intended service. Resilient materials, where used, are subject to service limitations as specified by the manufacturers. Use of resilient materials in valves intended for fire mains (see 4-7-3/1.11.1) is to be specifically approved based on submittal of certified fire endurance tests conforming to a recognized standard.