Computes total fluid pressure drop in a piping system, accounting for straight pipe friction (major loss), fittings & valves (minor loss), fixed equipment drops, and elevation changes (static head).
ΔP_major = f(L/D)(ρV²/2)
ΔP_minor = ΣK · (ρV²/2)
ΔP_fixed = Σ kPa
ΔP_static = ρgΔZ
System Variables
- L (Length): Total length of all straight pipes → ΔP_major = f(L/D)(ρV²/2)
- ΔZ (Elevation): Elevation change from start to end (positive = uphill, negative = downhill) → ΔP_static = ρgΔZ
- Minor Loss: Friction through fittings such as elbows and tees → ΔP_minor = ΣK · (ρV²/2)
- Fixed Drop: Fixed pressure drop across valves or specified equipment → ΔP_fixed = Σ kPa
⚠️ Gas Flow LimitationIf calculated pressure drop exceeds 10% of the inlet pressure for gases, compressible flow equations should be used for accuracy.
Recommended Velocities
Liquid (Discharge)1.0 - 3.0 m/s
Liquid (Suction)0.5 - 1.5 m/s
Gases & Vapors15.0 - 30.0 m/s
Need ε values? Pipe roughness reference →
Recommended values
- Pipe roughness: New CS 0.045 mm, stainless 0.015 mm, drawn tubing 0.0015 mm — age/corrosion raise it.
- Velocity: Liquid 1–3 m/s; design ΔP ≈ 0.3–1.0 bar/100 m for pumped lines.
- Flow regime: Laminar (Re < 2300) uses f = 64/Re; the Colebrook/Haaland fit applies to turbulent flow.
- Fittings: Add fitting losses via K (see the Minor-loss calculator) — straight-run friction alone under-reads.
Limitations
- Single-phase: Incompressible Darcy–Weisbach — not compressible (choked) gas or two-phase flow.
- Straight run: Covers straight pipe friction; fittings, elevation, and control valves are handled separately.
About the standards
- Darcy-Weisbach: Friction loss equation.
- Haaland: Friction factor approximation.