Source: https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/

instrument / verified-with-binding-errata

# Darcy-Weisbach Pressure Drop Calculator

The current ledger marks this instrument verified with errata that must be applied at binding time.

Status: **VERIFIED_WITH_ERRATA**Lifecycle: **verified-with-binding-errata**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/qualification/>)

## Ledger state

The current ledger marks this instrument verified with errata that must be applied at binding time.

**Area**: Thermodynamics, Fluids & Aero

**Tranche**: tranche-4

**Evidence ID**: t4-228

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The two displayed Darcy-Weisbach formulas are standard and mutually consistent because ΔP=ρg·hf. The instrument cannot receive a PASS until the exact automatic-friction-factor inputs, flow-regime rules, Colebrook implementation, unit conventions, and validation behavior are specified. The empty honest_label is a concern: the product should state that automatic f requires roughness and fluid-viscosity data and that the result is frictional loss only, excluding fittings, valves, elevation, acceleration, and other minor losses.

### Formula and scope findings

- The Darcy-Weisbach formulas are correct when f is the dimensionless Darcy friction factor: hf=f·(L/D)·(V²/(2g)) and ΔP=f·(L/D)·(ρV²/2). The specification must explicitly distinguish Darcy friction factor from the Fanning friction factor, which differs by a factor of four.

- The stated automatic Colebrook option is underspecified: it requires pipe absolute roughness ε, fluid viscosity μ or kinematic viscosity ν, and a defined Reynolds-number calculation. The Colebrook equation applies to turbulent flow; laminar and transition-flow handling is not specified.

- The Colebrook equation and solution method or convergence behavior are not provided, despite the engine being described as plain arithmetic.

### Unit assumptions

- f is dimensionless Darcy friction factor, not Fanning friction factor.

- L and D must use the same length unit; V must use length per time; g must use length per time squared; ρ must use mass per volume; ΔP then has pressure units consistent with those quantities.

- For SI calculations, use L and D in metres, V in m/s, g in m/s², and ρ in kg/m³; outputs are metres of head and pascals.

- The standard gravitational acceleration assumption is g=9.81 m/s² unless the user supplies another value.

- The pressure formula assumes a consistent mass-based unit system. US customary lbm-based inputs require the gravitational conversion constant gc; using lbf-based density/force conventions must be explicitly defined.

- For automatic f, absolute roughness ε and fluid viscosity are required in addition to the listed inputs.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

A zero pipe diameter produces undefined division in both formulas and must be rejected. The specification also leaves the explicit-f versus auto-Colebrook branch-selection convention and the sign convention for pressure drop insufficiently explicit.

## Errata and corrections

### Tranche errata

**head_loss_m** · vector 2

11.247706

11.238532

inconsistent with her own correct pressure_drop (110,029.5 Pa / rho*g = 11.2385)

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "f": 0.02,
    "L": 100,
    "D": 0.5,
    "V": 2,
    "rho": 1000,
    "g": 9.81,
    "units": "SI"
  },
  "expected_outputs": {
    "head_loss_m": 0.8154943935,
    "pressure_drop_Pa": 8000
  },
  "working": "L/D = 100/0.5 = 200. V²/(2g) = 2²/(2×9.81) = 4/19.62 = 0.2038735984 m. hf = 0.02×200×0.2038735984 = 0.8154943935 m. ρV²/2 = 1000×4/2 = 2000 Pa. ΔP = 0.02×200×2000 = 8000 Pa."
}
````

## Related workflows

[Pipe & Pump Benchfriction](<https://guthlabs.ai/docs/instrument-workflows/pipe-pump/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json · VERIFIED_WITH_ERRATA`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`