Any service valve that does not have an instrument such as a gauge in its port, what must an operator consider?

When a service valve does not have an instrument, such as a gauge, in its port, the operator must consider the presence of a plug. A plug serves as a closure device that can prevent flow through the valve when it is not in use. This is important for safety and system integrity, as it allows the operator to isolate portions of the system for maintenance or servicing without the risk of leakage or pressure loss.

Other options like a sight glass, thermometer, or regulator represent instruments that provide additional information or control mechanisms. However, in the case of a valve without a gauge, a plug remains a fundamental consideration for ensuring the proper sealing and safety of the system when a flow measurement or monitoring instrument is not in place. It emphasizes the need for operators to understand how to effectively manage service valves in various operational conditions.