When pumping four lines of 2-1/2 inch hose, each equipped with a 250 gpm fog nozzle at 100 psi, and each 300 feet long, the PDP required is most approximately:

• A. 244 psi
• B. 158 psi
• C. 138 psi
• D. 190 psi

Answer: (C)

Pumping four attack lines in parallel means the pump must overcome the friction loss in a single line to the nozzle, not the sum of all four lines’ losses. Each line carries 250 gpm through 2-1/2 inch hose for 300 feet, and the friction loss for that run is about 38 psi. The nozzle must receive 100 psi, so the pump discharge pressure is roughly 100 psi plus 38 psi, totaling about 138 psi. The four parallel lines don’t add their friction losses together because the pressure drop happens along each line independently; the pump only needs enough pressure to deliver the required 100 psi at the end of each line.