The Ford F-350 Super Duty doesn't have an "erg valve." There's no component with that name in its system. You might be thinking of another part, perhaps related to the EGR (Exhaust Gas Recirculation) system. The EGR valve location varies slightly depending on the engine (Power Stroke diesel or gas engine) and year of the truck. To find it, you'll need to consult a repair manual specific to your truck's year and engine.
If you can provide the year and engine type, I might be able to give you a more specific location. Otherwise, searching online for "[Your Year] Ford F-350 Super Duty EGR Valve location" should yield diagrams and information.
