What inputs are typically used in friction loss calculations for a 2.5-inch hose?

• A. GPM and hose length
• B. Nozzle size and discharge pressure
• C. Water temperature and humidity
• D. Time of day

Answer: (A)

Friction loss in a 2.5-inch attack hose is driven by how much water you’re moving and how far it has to travel. The flow rate (GPM) determines the resistance created by the water, and the hose length adds up that resistance over the distance. Using those two inputs, you can look up or calculate the friction loss per 100 feet for the 2.5-inch hose and then scale it by the actual length to get total friction loss. The nozzle size and discharge pressure help decide what you need at the nozzle, but they aren’t inputs to the friction loss calculation itself. Water temperature, humidity, and time of day don’t affect friction loss. So the typical inputs are flow rate and hose length.