|(a) Valves, valve packings, gaskets, and seats shall be suitable for the intended service and shall comply with the following: (1) Shutoff valves shall have a maximum allowable working pressure of at least the maximum allowable working pressure of the container. Leakage shall not occur at less than 1 1/2 times the maximum allowable working pressure of the valve. (2) Valve parts, except gaskets, packing, and seats that come in contact with the fuel shall be stainless steel, brass, or copper. (b) Valves shall be securely mounted and shielded or installed in a protected location to minimize damage from vibration and unsecured objects. (c) In vehicles whose engines do not incorporate an automatic shutoff in the engine fuel system, a positive shutoff valve shall be installed in the fuel supply line at the inlet to the pressure regulator. The shutoff valve shall automatically close and prevent the flow of fuel to the engine when the ignition switch is off or in the accessory position, or when the engine is not running and the ignition switch is on. (d) When multiple fuel systems are installed on the vehicle, automatic valves shall be provided as necessary to shut off the fuel not being used. (e) Fueling systems shall be equipped with a backflow check valve which will prevent the return of gas from the container to the filling connection. (f) Valves shall be installed so that their weight is not placed on or supported by the attached lines.