Which valve on a cargo tank is permitted to remain open during transportation?

The engine fuel line valve is the only valve that is permitted to remain open during transportation of liquefied petroleum gas (LPG) in a cargo tank. This is because the fuel line valve is associated with the engine's operation and is necessary for providing fuel to the engine for it to run during transit.

In contrast, the other valves are designed for safety and containment purposes. The pressure relief valve is crucial for releasing excess pressure and preventing tank rupture, and it must remain in a closed position to maintain the integrity of the system under normal transport conditions. The emergency shutoff valve is designed to stop the flow of gas in case of an emergency, and having it open during transportation could lead to risks if an emergency arose. The liquid withdrawal valve, which allows for the withdrawal of liquid LPG from the tank, should also remain closed to prevent accidental discharge or leaks during transport, as this poses significant safety and environmental hazards.

Understanding the role of each valve helps ensure safe transportation practices in compliance with NFPA 58 regulations, emphasizing the importance of only keeping certain valves open while ensuring the others are safely secured.