Friction Loss in Hose Lines

Key Concepts

• Friction Loss Identification: Essential for calculating required pump discharge pressures.
• Factors Influencing Friction Loss:
  • Volume of water flowing through the line
  • Size of the hose
  • Length of the hose

Friction Loss Calculation

• Standard Formula:
  • Uses three values:
    • Friction loss coefficient (from manufacturer)
    • Volume of water (in GPM)
    • Length of hose
• Calculation Process:
  • Begin with the friction loss coefficient provided by the hose manufacturer.
  • Multiply by Q squared (GPM divided by 100, then squared).
  • Multiply by L (length of hose divided by 100).

Practical Example

• Scenario: Standard pre-connect attack line (1¾" National 8D hose at 150 GPM)
  • Manufacturer's Coefficient: 12.49
  • Q squared = (150 / 100)² = 2.25
  • L (250 feet divided by 100) = 2.5
  • Friction Loss Calculation: 12.49 * 2.25 * 2.5 = 70 psi (14 psi per section)

Concepts of Friction Loss

1. Hose Length:

   • Longer hose = Greater friction loss
   • Shorter hose = Lower friction loss
   • Example: Reducing hose length by 100 feet drops total friction loss from 70 psi to 42 psi.

2. Volume of Water:

   • Increased volume = Increased friction loss (constant diameter)
   • Example: Increasing flow to 170 GPM raises friction loss to 95 psi (19 psi per section).
   • Decreasing flow to 130 GPM drops it to 52 psi (10 psi per section).

3. Hose Diameter:

   • Larger diameter = Exponentially decreased friction loss
   • Example: 150 GPM through a 2½" hose results in 15 psi total (3 psi per section), compared to 70 psi for 1¾".
   • For 500 GPM: 2½" hose = 25 psi per section vs. 3" hose = 10 psi per section.

Practical Considerations

• Hose Line Selection: Crucial for efficient pump utilization and reduced engine RPMs.
• Real-World Conditions:
  • Manufacturer values are ideal and may not reflect actual conditions.
  • Flow Testing: Regular testing to determine true friction loss values and pump pressures.

Conclusion

Understanding and calculating friction loss is vital for efficient fire service operations, ensuring proper pump discharge pressures and hose line selection. Regular flow testing is recommended to obtain accurate real-world data.