What must manufacturers do regarding the service ratings of valves?

Manufacturers are required to stamp or mark the valve body with the service rating to ensure that users can easily identify the specific capabilities and limits of the valve. This marking is a critical safety and compliance measure, as it provides essential information regarding the pressure and service conditions for which the valve is rated. By having this information directly on the valve, it helps prevent the misuse or installation of valves that may not be suitable for a particular application, thus promoting safety and efficiency in operations involving compressed natural gas.

In contrast, while other options may suggest alternative methods for indicating service ratings, none provide the direct and immediate identification that marking the valve body does. For instance, while providing a certificate of testing might demonstrate compliance, it does not offer real-time identification on the valve itself where it is needed most during installation or maintenance.