Regardless of how many zone valve boxes are installed on a lateral branch off a riser, only one what type of valve is required for each branch?

For each lateral branch off a riser in a medical gas system, it is necessary to install one service valve. The service valve serves an important function in medical gas systems, as it allows for the isolation of that specific branch from the rest of the system. This ensures that maintenance or service can be performed without disrupting the entire system and maintains the integrity and flow of the medical gases being supplied.

In contrast, while main, riser, and zone valves also play crucial roles in the distribution of medical gases, they are designed for different functions, such as controlling the flow from the main supply or isolating larger sections of the system. However, the service valve is the critical valve that specifically allows for service operations on the lateral branch itself, making it the required valve type for each lateral branch off the riser.