Engine Ops Tool
Friction Loss Calculator
Instantly calculate Friction Loss (FL) and Pump Discharge Pressure (PDP) for single hose lays. Essential for Driver/Engineers and fire academy students.
Formula: FL = C × Q² × L
Parameters
Friction Loss (FL)
0
PSI
Pressure lost due to hose lining drag
Total Pump Discharge Pressure (PDP)
0
PSI
Set your pump gauge to this value (FL + NP)
Understanding Friction Loss
Friction loss is the pressure lost in a fire hose as water moves through it. The faster the water moves (GPM) or the smaller the hose, the more pressure is lost.
The Formula
FL = C Q² L
- FL: Friction Loss (in PSI)
- C: Hose Coefficient (Roughness/Diameter)
- Q: Flow Rate (GPM divided by 100)
- L: Hose Length (Feet divided by 100)
Standard Coefficients (C)
| Hose Size | Coefficient (C) |
|---|---|
| 1 ½ inch | 24 |
| 1 ¾ inch | 15.5 |
| 2 ½ inch | 2 |
| 3 inch | 0.8 |
| 4 inch | 0.2 |
| 5 inch | 0.08 |
* Based on typical modern fire hose construction.
What is PDP?
Pump Discharge Pressure (PDP) is the total pressure the pump must generate. It accounts for the friction loss plus the pressure needed at the nozzle.
PDP = FL + NP (+/- Elevation)
* This calculator assumes level ground (no elevation change) and no appliance loss. For high-rise ops, add 5 PSI per floor (minus 1).
Worked Example (Quick)
Example: 1¾" hose (C=15.5), 150 GPM, 200 ft, NP=100 psi
- Q = 150/100 = 1.5
- L = 200/100 = 2
- FL = 15.5 × (1.5²) × 2 ≈ 69.75 → 70 psi
- PDP = FL + NP = 70 + 100 = 170 psi
Friction Loss FAQ
Friction loss is the pressure drop caused by water moving through the hose lining and couplings. Higher flow and smaller hose = higher FL.
Pump Discharge Pressure (PDP) is what you set on the pump gauge for that line. On level ground (no appliances): PDP = FL + NP.
Use standard C values for training and quick math. Use a custom C if your department provides tested hose coefficients/pump charts.
Training note: Always follow your department pump charts/SOPs and account for elevation and appliance/device loss when required.