Hose Lay Friction Loss Check
A crew is laying a supply line to a fire on the second floor of a commercial building. They plan to use 300 feet of 2½-inch hose from the hydrant to the pumper, then 200 feet of 1¾-inch hose from the pumper up to the fire floor. The pumper is rated to supply 1,000 gpm but the nozzle on the 1¾-inch line flows 150 gpm. The crew chief wants a quick estimate of whether the pumper can deliver enough pressure at the nozzle. The engine pressure available at the pumper is 150 psi. Friction loss for 1¾-inch hose at 150 gpm is roughly 35 psi per 100 feet. Friction loss for 2½-inch hose at 150 gpm is roughly 5 psi per 100 feet.
1. Estimate the total friction loss in the two hose sections and the nozzle pressure needed, then state whether 150 psi at the pumper is enough.
Read the worked answer
Compute each section separately, then add.
1¾-inch attack line:
- 200 ft = 2 lengths of 100 ft
- 35 psi per 100 ft x 2 = 70 psi
2½-inch supply line:
- 300 ft = 3 lengths of 100 ft
- 5 psi per 100 ft x 3 = 15 psi
Nozzle pressure (standard for a 1¾-inch handline): about 100 psi at the nozzle for a fog/combination nozzle, or about 50 psi for a smooth-bore. The problem does not specify, so state the assumption.
Using 100 psi nozzle pressure:
- Total = 70 + 15 + 100 = 185 psi
150 psi at the pumper is not enough under that assumption. The crew is short about 35 psi. Even ignoring the supply line, 70 + 100 = 170 psi already exceeds 150 psi.
2. What is one practical change the crew could make, and roughly how much would it help?
Read the worked answer
Several options, each with a rough effect:
- Shorten the attack line. Removing 100 ft of 1¾-inch hose saves about 35 psi, which closes most of the gap.
- Switch to a larger attack line (2½-inch) for the same flow. At 150 gpm, 2½-inch loss is about 5 psi per 100 ft, so 200 ft costs only ~10 psi instead of 70 psi - a saving of about 60 psi, more than enough.
- Reduce nozzle pressure if a lower-pressure nozzle is acceptable, but only within the nozzle's rated operating range; do not starve the stream.
- Add a second supply line or relay to reduce supply-line loss, though the supply line is only 15 psi here, so this helps least.
The best single fix is the larger attack line or a shorter lay, because the attack line dominates the loss.