Parallel Pipe Network Calculator

Calculate flow distribution and shared head loss for two pipes connected in parallel using the Darcy-Weisbach equation.

Pipe Networks · Parallel

Fluid Presets

Diameter unit:

Pipe 1

Length L₁ (m)

Diameter D₁ (mm)

Roughness ε₁ (m)

Pipe 2

Length L₂ (m)

Diameter D₂ (mm)

Roughness ε₂ (m)

Flow Conditions

Total flow rate Q (L/s)

Fluid density ρ (kg/m³)

Dynamic viscosity μ (Pa·s)

Q = 20 L/s = 0.020000 m³/s

Theory

Parallel Network Principles

hf₁ = hf₂ = hf (equal head loss across all branches)

Q = Q₁ + Q₂ (continuity — flows add)

Conductance Method

Qᵢ = Cᵢ × √(hf) (branch flow)

Cᵢ = Aᵢ × √(2g Dᵢ / (fᵢ Lᵢ)) (conductance)

hf = (Q / ΣCᵢ)² (solve for hf)

Qᵢ = Cᵢ × Q / ΣCᵢ (branch flow split)

Friction Factor

Laminar (Re < 2300): f = 64/Re

Turbulent (Re ≥ 2300): Swamee-Jain approximation (iterated)

Typical Pipe Roughness

Material	ε (m)	ε (mm)
PVC / drawn tubing	1.5×10⁻⁶	0.0015
Commercial steel	4.6×10⁻⁵	0.046
Galvanized steel	1.5×10⁻⁴	0.15
Cast iron	2.6×10⁻⁴	0.26
Concrete	1×10⁻³	1.0

Flow distributes so that head loss is identical across all branches. A branch with a larger diameter or shorter length carries a disproportionately larger share because its conductance scales roughly as D^2.5/√L.