How do I get K from L/D?

K = f_T × (L/D). FEK stores Crane-style f_T by NPS band (e.g. NPS 2 → 0.019). Total K multiplies by quantity.

Why not use this for viscous / laminar flow?

Crane L/D and f_T assume turbulent commercial-steel pipe. For Re < ~2000 or high viscosity, use 2-K or Darby 3-K methods — this tool is screening only.

Which calculator should I open next?

Carry NPS/schedule into pressure-drop-friction for line ΔP, or pipe-wall-thickness for B31.3 wall checks.

Piping Equivalent Length Calculator (Fittings & Valves) — 3" Sch 80 · 45° elbow | FieldEngineersKit

Parameter	Value
Nominal pipe size (NPS)	3"

1. Formula & conversion factors

Crane Technical Paper No. 410 — Flow of Fluids Through Valves, Fittings, and Pipe (Ch. 2 & Appendix A) · ASME B36.10M / B36.19M — Welded and Seamless Wrought Steel Pipe · ASME B16.9 / B16.10 — Fitting and valve dimensional context (geometry reference)

L_eq = (L/D) · D_i

K = f_T · (L/D) · L_eq = K · D_i / f_T

Crane TP-410 L/D · fully turbulent f_T · ASME B36.10M/B36.19M inside diameter

Hero L_eq (unit-aware)Source Crane TP-410K f_T × L/DID B36 schedule

Equivalent length converts fittings and valves into an equal length of straight pipe for Darcy–Weisbach pressure-drop screening. L/D and f_T follow Crane TP-410 fully turbulent steel-pipe practice. Di is the ASME B36 schedule inside diameter. Not for laminar / high-viscosity regimes — use 2-K or Darby 3-K methods there.

L_eq (Equivalent length) — Straight-pipe length with the same frictional loss as the fitting (m or ft).
L/D (Length-to-diameter ratio) — Crane TP-410 published ratio for the fitting or valve (dimensionless).
D_i (Inside diameter) — Pipe ID from ASME B36.10M / B36.19M for the selected NPS × schedule.
f_T (Fully turbulent friction factor) — Crane chart f_T for commercial steel pipe at the NPS band.
K (Resistance coefficient) — K = f_T × (L/D); total K scales with quantity.

2. Quick reference lookup table

Crane TP-410 screening L/D ratios (selected fittings & valves)
Fitting / valve	L/D	Group	Notes
90° elbow, standard (r/D ≈ 1)	30	Elbow	Most common process elbow
90° elbow, long radius (r/D ≈ 1.5)	16	Elbow	Lower loss than std
45° elbow, standard	16	Elbow	—
Tee — flow through run	20	Tee	Straight-run path
Tee — branch flow	60	Tee	Into/out of branch
Gate valve, full open	8	Valve	Low loss
Globe valve, standard	340	Valve	High loss
Swing check valve	100	Valve	—
Ball valve, full bore open	3	Valve	Nearly full bore
Butterfly valve, full open	45	Valve	—

L/D values are Crane TP-410 turbulent screening defaults used in this calculator. Manufacturer Cv/K data overrides Crane when available for purchase sizing.

3. How to use this calculator

1
Select NPS and schedule
NPS sets Crane f_T; schedule sets ASME B36 inside diameter D_i.
2
Choose fitting or valve
Pick the Crane TP-410 component — L/D is shown on each option.
3
Enter quantity
Total L_eq and K scale linearly with the number of identical fittings.
4
Read L_eq and K
Hero shows total L_eq with the active unit first; badges list D_i, L/D, K, and f_T.

4. Engineering FAQ

L/D is Crane TP-410’s ratio of equivalent straight-pipe length to inside diameter for a fitting or valve under fully turbulent flow. L_eq = (L/D) × D_i.