If the pump operator is supplying 3 lines and has his relief valve set and one of the firefighters shuts down his nozzle, the pump operator will see the following reaction on his panel:

• A. Only decreased pressure
• B. All of the above
• C. No change
• D. Only increased pressure

Answer: (B)

When the pump is feeding three lines and one nozzle is shut, the overall demand decreases. If you keep the same throttle setting, the pump will push the same amount of water, so the discharge pressure in the system tends to rise. The relief valve is set to open at a specific pressure, so as that pressure is reached, the valve will begin to relieve flow, which can lower the discharge pressure back down. Because of this feedback, the panel can show different readings at different moments: you can see an increase in pressure on the lines still in use before relief action offsets it, a decrease in pressure once the relief valve diverts water, or momentary no net change as the system stabilizes. Since the sequence can produce any of these outcomes during the transition, all of the above is the best description of what the operator might observe on the panel.