Which valve serves as the tank outlet valve in a Type 3 system?

In a Type 3 system, the tank outlet valve is designed to ensure safe and effective operation when handling liquid fuels and fluids. The non-lubricated double block and bleed valve is particularly suited for this purpose due to its ability to provide two separate sealing mechanisms and a bleed port that allows for pressure release between the two seals.

This feature is critical in a Type 3 system because it enhances safety by reducing the risk of leaks or contamination when isolating the tank from the system. If maintenance is needed or if there is a procedure that requires the tank to be isolated, the double block and bleed valve ensures that there are no risks of fluid passing through the valve inadvertently.

In contrast, other types of valves like ball valves, lubricated plug valves, and rising stem gate valves may not offer the same level of isolation or safety features needed for a fuel system outlet. They may work well in various applications but lack the specialized design required for maximizing safety and preventing leaks in a system where liquid fuels are handled. Therefore, the non-lubricated double block and bleed valve is the most appropriate and effective choice for the tank outlet valve in a Type 3 system.