What is a characteristic of valves meant to be used as primary stop valves?

Primary stop valves are critical components in gas distribution systems, including those used in compressed natural gas delivery. Their design and material specifications are essential to ensure reliability, safety, and performance under pressure conditions.

The characteristic highlighted in the correct answer emphasizes that primary stop valves must be made of cast iron that complies with specific ASTM specifications. Cast iron is chosen for its high strength, excellent durability, and ability to withstand the rigors associated with gas transportation and storage. Compliance with ASTM specifications ensures that the valve meets industry standards for performance, safety, and reliability, which is crucial for preventing leaks and ensuring safe operations during gas delivery.

Using cast iron that adheres to these standards provides assurance that the valve can handle the pressures and stresses encountered in a compressed natural gas system, making it a suitable choice for primary stop valves.