What type of valve shall be used at the point of connection when a gas system has supplementary standby gas connected downstream of the meter?

The use of a three-way valve at the point of connection when a gas system has supplementary standby gas connected downstream of the meter is appropriate because it allows for flexibility in directing the flow of gas from different sources. A three-way valve can direct gas either from the primary supply or the supplementary standby supply to the system, allowing a smooth transition between gas sources as needed. This capability is crucial for ensuring a consistent gas supply while providing the option to switch to the standby system during outages or maintenance.

Moreover, three-way valves are designed to facilitate the mixing or diverting of gases, which is vital for operations where reliability and adaptability are important. In a scenario where a standby gas source is needed, this type of valve allows for immediate changes in the gas supply without the need for additional manual adjustments or installations.

The other valve types, while useful in their contexts, do not provide the required functionality of directing gas from multiple supply lines. A ball valve and a shut-off valve serve specific purposes like completely stopping the flow of gas, which is not sufficient for managing two different gas sources concurrently. A check valve is designed to prevent backflow but does not have the functionality to switch between gas supplies. Therefore, a three-way valve is the most effective choice for