In the same friction loss formula, what does L represent?

• A. Length of the hose in hundreds of feet
• B. Flow rate in hundreds of GPM
• C. Friction loss coefficient
• D. Pressure drop per 100 feet

Answer: (A)

Length of the hose being used. Friction loss grows with the distance water travels—the longer the hose, the more contact and resistance, so more pressure is lost to friction. In the standard friction loss formulas used in firefighting hydraulics, L is included as a factor for hose length and is often expressed in tens or hundreds of feet to keep the constants convenient. That means doubling the hose length at the same flow increases friction loss proportionally. The flow rate is handled by the Q term, and the friction loss coefficient is a separate constant tied to hose diameter and roughness. The pressure drop per 100 feet is simply a way to report the result, not what L represents.