Friction loss in a firefighting hydraulic system is the pressure drop caused by water flowing through hoses and pipes. It is influenced by which factors?

• A. The pressure increase due to water acceleration
• B. The pressure at the nozzle outlet
• C. The pressure drop caused by water flowing through hoses and pipes; influenced by flow rate, hose diameter, length, roughness of the interior, fittings, and temperature.
• D. The pressure needed to overcome gravity only

Answer: (C)

Friction loss is the pressure drop that occurs as water moves through hoses and pipes, due to resistance from the interior surfaces and fittings. This loss increases with how fast the water is moving and with how long and narrow the passage is, because higher flow rates mean higher velocities and more contact with walls over a longer distance. It also grows with rougher interior surfaces, since roughness creates more drag and turbulence. Additional fittings, elbows, adapters, and valves introduce extra local losses beyond a straight run. Temperature matters because water viscosity changes with temperature, so hotter water flows with slightly less resistance, reducing friction loss a bit.

So the best description is the one that states friction loss is the pressure drop caused by water flowing through hoses and pipes, and that it is influenced by flow rate, hose diameter, length, interior roughness, fittings, and temperature. The other ideas—involving pressure changes from acceleration, nozzle outlet conditions, or gravity alone—don’t capture the specific resistive losses occurring inside the hydraulic run.