What type of configurations may use a 3-way valve in gas systems?

The use of a 3-way valve in gas systems is primarily to manage metered and unmetered supplies. This configuration allows for a more flexible control of gas flow, enabling the system to utilize different sources of gas as needed. For instance, in systems where both metered (charged) and unmetered (free-flowing) gas are available, a 3-way valve can help in switching between these sources effectively, ensuring that the system operates efficiently and safely.

Metered supplies are typically monitored and regulated to ensure accurate billing and usage tracking, while unmetered supplies may come from sources like emergency backup systems. Utilizing a 3-way valve for this purpose enhances system versatility and reliability by allowing smooth transitions between supply types without interrupting service.

In contrast, configurations that limit the use of 3-way valves to only high-pressure systems, residential installations, or automatic purging systems do not fully encompass the valve's versatility and applicability across various gas supply setups. The core advantage lies in the ability to manage different gas supplies, which is the reason B is the most accurate choice.