What is the approximate engine pump pressure necessary to deliver 600 gpm through a fog nozzle on a deck gun using three (3) 2-1/2" lines? The lines are 400 feet long and the deck gun is elevated 20 feet above the pumper. (Deck gun FL = 10psi)

• A. 130 psi
• B. 170 psi
• C. 150 psi
• D. 180 psi

Answer: (C)

Delivering 600 gpm through three equal lines means each line carries about 200 gpm, and the pressure needed comes from the nozzle plus all losses in the supply path and any elevation head. For 2-1/2 in hose at 200 gpm over 400 ft, friction loss is about 32 psi per line. Since the lines are parallel, you don’t add losses from all lines—you use the loss along the path to the deck gun, which is the same 32 psi in this case. The deck gun itself contributes 10 psi of friction loss. Elevation adds head: 20 ft of rise equals about 8.7 psi (20 ÷ 2.31). A fog nozzle delivering 600 gpm typically requires about 100 psi at the nozzle. Add these together: 100 + 32 + 10 + 8.7 ≈ 150.7 psi, so roughly 150 psi.

130 psi would underrepresent the losses and nozzle pressure; 170 or 180 psi would exceed typical nozzle requirements for this flow.