Which hose size yields 259.45 kPa friction loss at 75 m and 375 l/min?

• A. 38 mm
• B. 45 mm
• C. 65 mm
• D. 75 mm

Answer: (B)

Friction loss in a fire hose depends on how far the water has to travel (length), how fast it’s moved (flow), and the hose diameter. For a given length and flow, a larger diameter reduces friction loss because the water moves more slowly and there’s less turbulence per unit area, while a smaller diameter increases friction loss.

At 75 meters and 375 liters per minute, the hose size that yields a friction loss of 259.45 kPa is 45 millimeters. If you used a smaller diameter like 38 mm, the friction loss would be higher than the target value, and with larger diameters such as 65 mm or 75 mm, the friction loss would be lower than the target.