What is a key feature of CNG vehicle cylinder valves?

A key feature of CNG vehicle cylinder valves is that they must have a manual valve or a remotely actuated shutoff valve. This is essential for safe operation because these valves control the flow of compressed natural gas from the storage cylinders to the engine. A manual valve allows the driver or technician to manually shut off the gas flow, which is crucial in emergencies or during maintenance. A remotely actuated shutoff valve can be controlled from inside the vehicle or from a distance, providing added safety and convenience. This design feature ensures that the vehicle can be operated safely and effectively by allowing for quick and reliable access to control the gas flow.

The other choices do not meet the safety and regulatory standards for CNG vehicles. For instance, cylinder valves being located anywhere on the vehicle could pose a safety risk and may be against regulations that dictate specific installation requirements. Additionally, materials used for valves need to be compatible with CNG to ensure durability and prevent leaks, which rules out using any material. Finally, making valves removable without tools could compromise safety by allowing them to be disconnected too easily, leading to potential gas leaks or other hazards. The regulation of valve type and functionality is a fundamental aspect of CNG vehicle design to ensure safety during operation.