What must a vapor service valve (POL) be equipped with when disconnected?

A vapor service valve must be equipped with a plug or cap when it is disconnected to ensure safety and prevent leaks. This requirement is crucial because it helps contain any potentially dangerous gases or vapors that might escape from the valve when it is not in use. By sealing the opening, a plug or cap serves to protect both the equipment and the surrounding environment from exposure to hazardous materials.

In addition, this practice is an important safety measure in the handling of pressurized systems, ensuring that there is no accidental release of vapors that could lead to safety incidents. It highlights the importance of maintaining proper equipment integrity and safety protocols in the field.

The other options are not correct in this context because they do not adequately address the specific safety requirement associated with a disconnected vapor service valve. A filter would not serve to seal the valve, a gauge does not prevent leaks, and while a sealant may provide a form of closure, it is not a standard requirement for disconnected valves.