A shut-off valve shall be provided in the main supply line when the source valve is not accessible from within the building served. What is the name given to this valve?

The valve referred to in the question is known as the main valve, and it plays a crucial role in the safe management of medical gas supply systems. The main valve is critical for isolating the gas supply from the overall system, particularly in situations where access to the source valve—often located outside the building—is not readily available.

This isolation is important for maintenance, emergencies, or when repairs are necessary. By ensuring that the main supply line has a shut-off valve, facilities ensure that they can safely control the flow of gas, minimizing the risk of leaks or accidents within the building.

In contrast, branch valves and riser valves serve different purposes related to distribution and control within the system but do not directly serve the function of controlling the main supply line in the context described. A supply valve generally refers to a valve that is used further down in the system to control the supply to specific areas or equipment but does not perform the critical isolation function as described in the question. The focus on having a main shut-off valve in the main supply line highlights the importance of safety and access in medical gas systems.