What was found
FLT 718 FROM STL TO ELP, ON CLIMB FROM STL, NR 3 ENGINE START VALVE LIGHT ILLUMINATED AT 15000 FT. SHUTDOWN NR 3 ENGINE AS A PRECAUTION. DUMPED 6000 LBS OF FUEL, RETURNED TO STL, AND LANDED WITHOUT INCIDENT. FOUND NR 3 ENGINE START VALVE INOPERATIVE. REPLACED START VALVE. AIRCRAFT RETURNED TO SERVICE.