Fire Hose Friction Loss Calculator
Calculation Results
Total Friction Loss: 0 PSI
Friction Loss per 100ft: 0 PSI
Estimated Pump Discharge Pressure (PDP): 0 PSI
*Calculations are based on the standard formula: FL = C * (Q/100)² * (L/100)
Understanding Fire Hose Friction Loss
In the fire service, calculating friction loss accurately is critical for ensuring that firefighters at the nozzle receive the correct water pressure and volume to effectively extinguish a fire. Friction loss is the energy lost due to the turbulence of water moving through the interior of a hose and the resistance created by the hose lining.
The Friction Loss Formula
The standard industry calculation for friction loss in fire hoses is:
FL = C × (Q/100)² × (L/100)
- FL: Friction Loss in Pounds Per Square Inch (PSI).
- C: Friction Loss Coefficient for the specific hose diameter.
- Q: Flow rate in Gallons Per Minute (GPM).
- L: Total length of the hose in feet.
Common Friction Loss Coefficients (C)
| Hose Diameter | Coefficient (C) |
|---|---|
| 1.5 Inch | 24 |
| 1.75 Inch | 15.5 |
| 2.5 Inch | 2 |
| 3 Inch (with 2.5″ couplings) | 0.8 |
| 5 Inch (LDH) | 0.08 |
Real-World Example
Imagine you are operating a 200-foot line of 1.75-inch hose with a nozzle flowing 150 GPM. To find the friction loss:
- Identify the coefficient (C) for 1.75″: 15.5
- Calculate the flow factor: (150 / 100) = 1.5. Square it: 1.5 × 1.5 = 2.25.
- Calculate the length factor: (200 / 100) = 2.
- Multiply them all: 15.5 × 2.25 × 2 = 69.75 PSI.
If you wanted a nozzle pressure of 75 PSI, your pump discharge pressure (PDP) would need to be roughly 145 PSI (75 + 69.75 + any elevation loss).
Factors That Influence Friction Loss
- Hose Condition: Older hoses with rougher inner linings create more friction.
- GPM: If you double the flow rate, the friction loss increases fourfold (because it is squared in the formula).
- Hose Length: Friction loss is directly proportional to length. Double the hose length, double the loss.
- Kinks: Sharp bends or kinks in the hose significantly increase resistance and reduce flow.
Frequently Asked Questions
Q: Why is friction loss important?
A: If the pump operator doesn't account for friction loss, the firefighters at the nozzle will not have enough pressure to produce an effective stream, compromising fire suppression and safety.
Q: Does elevation affect these numbers?
A: Yes. This calculator focuses on friction loss. For elevation, add 5 PSI for every 10 feet (one floor) of elevation increase.
Q: Is LDH (Large Diameter Hose) better?
A: Yes, for moving large volumes of water. Because the coefficient for 5″ hose is only 0.08, you can move much more water with significantly less pressure loss compared to smaller lines.