Reverse-Lay Friction Loss
Supply friction loss for one line, and per line when n parallel lines share the flow...
Example
You enter
- Hose diameter 2.5_in
- Total flow (gpm) 250
- Length (ft) 600
- Number of parallel supply lines (sharing the flow) 2
You get
- Friction if one line carried it all 75 psi
- Friction per parallel line 18.8 psi
- Parallel lines 2
- Coefficient 2
Checked against published worked examples from: IFSTA Pumping Apparatus / NFPA 1962 hose-friction tables.
Details, formula, and sources
ScopeSupply friction loss for one line, and per line when n parallel lines share the flow (each loses 1/n^2 of the single-line figure).
Formula or tableOne line: FL = C × Q² × L. n parallel lines sharing the flow: FL_per_line = FL_single / n², each carrying Q/n. (Pumps in tandem on one line share the single-line loss; they do not reduce it.)
Source and editionNFA hose-hydraulics training materials by name.
Free accessFree at usfa.fema.gov/training.
What governsEstimate. AHJ and licensed fire protection engineer govern.
API field nameshose_diameter, gpm, length_ft, n_pumps, single_pump_psi, per_pump_psi, coefficient
- Equal flow split Q / n per parallel hose unless user supplies a measured imbalanceengineering practice