What is meant by the design pressure for a protected system?

• A. The minimum operating pressure required for normal system operation.
• B. The operating pressure the protected system is designed to maintain under fire conditions.
• C. The pressure at which the relief valve should open under all conditions.
• D. The static pressure at pump discharge when the system is idle.

Answer: (B)

The main idea is: design pressure is the pressure the protected system is meant to hold during fire conditions so it can deliver the required water flow everywhere in the system. This pressure is used when sizing and evaluating components like pumps, pipes, and valves, ensuring that even with flow demands and friction losses, the system can maintain adequate pressure where it’s needed most. It’s about performance under fire demand, not about normal idle operation or safety valve settings. So the design pressure describes the level the system should maintain when it’s actively fighting a fire, which is why it’s the best match for this concept.