Describe how to determine an initial engine discharge pressure when given a target nozzle pressure and known friction losses.

• A. Add all friction losses (attack and supply lines) and any elevation losses to the target nozzle pressure to obtain the required discharge pressure; confirm with a test and adjust as needed.
• B. Subtract all losses from the target nozzle pressure.
• C. Use only the nozzle pressure as discharge pressure and ignore losses.
• D. Double the nozzle pressure to account for losses.

Answer: (A)

To deliver the intended nozzle pressure, you must account for pressure losses that occur between the pump discharge and the nozzle. Friction in the attack lines, friction in the supply lines, and any elevation gains all reduce the pressure by the time water reaches the nozzle. Therefore, you add those losses to the target nozzle pressure. The initial engine discharge pressure is the sum of the target nozzle pressure plus all known friction losses and any elevation losses. After setting that initial pressure, you should test by flowing water and adjust as needed because actual losses can vary with hose length, diameter, fittings, and flow. This approach ensures the nozzle receives the desired pressure despite the resistance in the hose system. Subtracting losses would under-pressurize the nozzle, relying on only the nozzle pressure ignores system friction, and doubling the nozzle pressure isn’t a method grounded in assessing hose losses.