Crane TP-410 • Hooper 2-K • Darby 3-K Methods | Pressure Drop & Equivalent Length
Calculate pipe fitting equivalent lengths and K values instantly using industry-standard Crane TP-410, Hooper 2-K, and Darby 3-K methods. This free calculator determines pressure drop coefficients for elbows, tees, valves, and other pipe fittings with no signup required.
Understand K-factor methods, Reynolds effects, and friction loss fundamentals
| Method | Formula |
|---|---|
| Crane | K = (L/D) × fT |
| Hooper 2-K | K = K₁/Re + K∞(1 + 1/D) |
| Darby 3-K | K = Km/Re + Ki(1 + Kd/D0.3) |
Pressure drop: ΔP = K × ρV² / (2g × 144) [psi]
For Re > 10,000 in 1"–10" pipe, all three methods typically agree within 15%.
K values are dimensionless loss coefficients that represent pressure drop as velocity heads (ΔP = K × ρV²/2g), while equivalent length converts fitting losses to equivalent straight pipe length. Equivalent length = K × D / (4f), where D is diameter and f is friction factor.
Darby 3-K is most accurate across all flow conditions as it accounts for Reynolds number and pipe size effects. Hooper 2-K adds Reynolds correction over Crane. For turbulent flow (Re > 10,000), all methods typically agree within 15%. Crane TP-410 is fastest and most conservative.
Pressure drop = K × ρV² / (2g × 144) in psi, where K is the loss coefficient, ρ is fluid density (lb/ft³), V is velocity (ft/s), and g is gravity (32.174 ft/s²). The factor 144 converts from lb/ft² to psi.
For a standard 90° elbow (r/D=1), typical K values are: Crane method K = 30×fT (≈0.48 for 4" pipe), Hooper 2-K gives K = 800/Re + 0.14, and Darby 3-K gives K = 950/Re + 0.25×(1+1/D^0.3). Long radius elbows have lower K values.
Yes, K values are additive for fittings in series in the same pipe section: K_total = K1 + K2 + K3 + ... Total pressure drop = K_total × ρV² / (2g × 144). This assumes no flow recovery between closely spaced fittings.