How must shutoff valves be designed in relation to system working pressure?

Answer: B — Must have a design working pressure not less than the rated system pressure

The correct choice emphasizes that shutoff valves must have a design working pressure that is not less than the rated system pressure. This requirement is crucial for safety and operational integrity in a compressed natural gas (CNG) system. If the design working pressure of a shutoff valve is lower than the system's operating pressure, there is a significant risk of failure. Such failure could lead to leaks or catastrophic ruptures, posing serious hazards, including fire, explosion, or release of natural gas into the environment. Therefore, selecting valves with a design pressure matching or exceeding the system's rated pressure ensures that they can withstand operational demands while maintaining safety. In CNG applications, where pressures are typically quite high, using components that can handle those pressures without risk of failure is essential for protecting both the equipment and personnel working with the system. This is why regulations and best practices require that shutoff valves maintain a design working pressure that meets or exceeds the system's rated pressure. This approach helps mitigate risks associated with high-pressure systems and ensures reliable operation.