What type of valves should not have removable stems without disassembly of the valve?

The correct answer pertains to valves designed for Compressed Natural Gas (CNG) applications. In CNG systems, safety and reliability are critical due to the high pressures involved. Valves specifically designed for CNG applications are constructed to prevent leaks and are equipped with features that ensure they can effectively handle the operational demands without compromising safety.

Removable stems in valves can introduce points of failure or leaks if not properly sealed. In high-pressure applications like those in CNG systems, it is essential that any components that could be disassembled do not create risks. Therefore, valves in CNG applications are typically designed to be integral, without removable stems that could be disassembled without the entire valve being taken apart. This design choice enhances the durability and safety of the system by minimizing the potential for human error during maintenance and reducing the likelihood of pressure-related failures.

On the other hand, manual valves, high-pressure safety valves, and ball valves may have designs that accommodate removable stems, depending on their intended use and application requirements. Each of these types of valves can be engineered for different functionalities, which may allow for maintenance or replacement of parts without requiring full disassembly in less critical applications where safety margins are different.