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

instrument implementation / implementation-contract

# Darcy-Weisbach Pressure Drop Calculator implementation

A source-bound implementation contract for Darcy-Weisbach Pressure Drop Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_WITH_ERRATA**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

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

**Evidence ID**: t4-228

**Effect**: Computation or source lookup only

## Input and validation requirements

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.

## Required corrections

````
[
  {
    "vector": 2,
    "field": "head_loss_m",
    "wrong": 11.247706,
    "correct": 11.238532,
    "cause": "inconsistent with her own correct pressure_drop (110,029.5 Pa / rho*g = 11.2385)"
  }
]
````

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "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."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/darcy-weisbach-pressure-drop-calculator/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

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

- `tranche errata record`