Only one service valve is required for each branch off the riser, unless the number of zone valves on that branch exceeds ______ valves?

Only one service valve is required for each branch off the riser, unless the number of zone valves on that branch exceeds ______ valves?

• A. 6
• B. 8
• C. there is no maximum
• D. 4

Answer: (D)

The key idea is safe isolation of a branch off the riser when maintenance or testing is needed. A single service valve normally isolates the entire branch, but as the number of zone valves on that branch increases, isolating a specific portion or performing work without affecting all zones becomes harder with only one service valve. When there are more than four zone valves on the branch, a second service valve (or more) is needed to segment the branch and provide proper isolation for maintenance. Therefore, four is the threshold: one service valve is sufficient when there are four or fewer zone valves; exceeding four requires an additional service valve.

The key idea is safe isolation of a branch off the riser when maintenance or testing is needed. A single service valve normally isolates the entire branch, but as the number of zone valves on that branch increases, isolating a specific portion or performing work without affecting all zones becomes harder with only one service valve. When there are more than four zone valves on the branch, a second service valve (or more) is needed to segment the branch and provide proper isolation for maintenance. Therefore, four is the threshold: one service valve is sufficient when there are four or fewer zone valves; exceeding four requires an additional service valve.