PackBuilt · in the lab

Pipe fitting loss constants (2-K and 3-K) - DRAFT

Use this add-on:

Lab Also adds 1 item it needs (2.5 MB).

Screenshots and a short video come with the listing (AL.3).

Overview

A table of loss coefficients for pipe fittings and valves, in two forms: the 2-K method (Hooper, 1981) and the 3-K method (Darby, 1999). It is the table behind the Fitting losses calculator and the fitting lists on pipe network links in the P&ID add-on and the Plant tab. THIS TABLE IS A DRAFT. Its constants were taken from the tables of the MIT-licensed fluids library (Caleb Bell) and have not yet been checked against the original papers by an engineer. A community test asks for that check.

Who it’s for

Process and piping engineers who need a loss coefficient for a fitting or valve while sizing a line or checking a network.
Reviewers with a copy of Hooper (1981), Darby (1999) or Crane Technical Paper 410 who can confirm the numbers.

What you can do

Pick a fitting or valve from the list in the Fitting losses calculator and get its K and head loss for your Reynolds number and pipe size.
Put a list of fittings on a pipe network link: the K is worked out again at each step from that link's own flow and diameter, and added to the K you typed.
Replace the table with your own pack in the same format if you have checked numbers.

Methods and standards

The 2-K form is K = K1/Re + Kinf (1 + 1/D) with D the actual inside diameter in inches. The 3-K form is K = K1/Re + Ki (1 + Kd/D^0.3) with D the nominal size in inches. The formulas are written in this project. The pack holds only the constants and the fitting names.

Data and sources

Each entry has the source's name, a plain label, a category (elbow, tee or valve) and its constants. The 2-K table has 32 entries and the 3-K table 34. The constants were copied from the Hooper and Darby tables of fluids/fittings.py (https://github.com/CalebBell/fluids, MIT licence). Six 2-K entries have source names that look odd (four filed under 'Elbow, Elbow' or 'Used as', 'Tee, Tee, Stub-in', and a 45-degree screwed elbow whose constants are larger than the other 45-degree elbows); they are kept as named and marked for the check. Primary publications: Hooper, W. B., 'The 2-K Method Predicts Head Losses in Pipe Fittings', Chem. Eng. 88(17), 1981; Darby, R., 'Correlate Pressure Drops through Fittings', Chem. Eng. 106(7), 1999.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Verification

Draft. tools/process-test/test-fittingk.mjs checks the pack against the fluids tables row by row, reproduces the worked examples in the source, and checks counts and duplicates. It does not check the numbers against the papers. No engineer has done that yet; the community test CH10-FITTING-K asks for it. Until it is done the review state in the pack is draft and every result says so.

Limits

Draft constants, not checked against the papers. The 2-K and 3-K methods are correlations fitted for the fittings and flows the papers cover; outside them the result is an extrapolation. The K1/Re term matters at low Reynolds numbers. The result is a calculation aid, not an engineering approval.

Files and formats

A data pack in the format cadcraft-fitting-k-pack (version 1), JSON. Nothing is written to your drawings except the K you choose to type on a link.

Get started

Open the P&ID add-on or the Plant tab, then Calculators, then Fitting losses.
Pick a fitting from the list, give the Reynolds number and the pipe size in inches, and read K and the head loss.
To use fittings in a network, open the Pipe network calculator and add a fit list to a link.

Languages

No languages are listed for this add-on yet. Its maker may add some.

Works in

Edition	Works	Note
Browser (/use) (yours)	Added on demand	Fetched the first time you use it, then kept for offline use.
Studio from getcadcraft.com	Added on demand	Fetched the first time you use it, then kept for offline use.
Microsoft Store	Added on demand	Fetched the first time you use it, then kept for offline use.
Google Play	Added on demand	Fetched the first time you use it, then kept for offline use.
iPad and iPhone (App Store)	Added on demand	Fetched the first time you use it, then kept for offline use.
Custom build	Added on demand	Fetched the first time you use it, then kept for offline use.

Comes with

Process engine 2.5 MB

Adding it brings these too. Engines are shared: each downloads once for every add-on that uses it.

Versions

Version	Channel	Date	What changed
1.0.0	lab	October 31, 2026	First version in the Library.

Licence and maker

CadCraft (CadCraft, first-party). Licence: Apache-2.0. Dependencies carry their own licences, listed on their pages.