Source: https://guthlabs.ai/docs/instruments/npsh-available-calculator/mechanism/

instrument mechanism / verified-clean

# NPSH Available Calculator mechanism

The inspectable method record for NPSH Available Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The arithmetic is standard and correct under the stated assumptions, but the instrument needs explicit inputs or defaults for fluid density, absolute-pressure handling, hs sign convention, vapor-pressure interpolation, and the exact definition of NPSHr comparison. The existing honest label appropriately limits the result to a cavitation-risk estimate and should be retained.

- The stated NPSHa formula is standard only for an open reservoir exposed to the specified atmospheric absolute pressure, with hs defined as free-surface elevation minus pump suction-center elevation; this applicability condition is not explicit.

- The output margin formula is not stated; it should be margin = NPSHa - NPSHr, with both values referenced to the same flow rate, speed, fluid, and datum.

- Fluid density rho is required by the formula but is absent from the listed inputs; assuming water without allowing temperature-dependent density can introduce error.

- The vapor-pressure lookup must define its interpolation method. Linear interpolation is used in the test vectors, but this is not specified in the instrument description.

## Units and conventions

- All pressures are absolute and entered in kPa in the user-facing inputs; they are converted to Pa before division by rho*g.

- Static suction head hs and suction loss hf,suction are in metres of fluid; hs is positive for flooded suction and negative for suction lift.

- rho is in kg/m^3, g is in m/s^2, and the resulting NPSHa and margin are in metres of water.

- NPSHr must be entered in metres of the same fluid and at the operating flow rate and pump speed being evaluated.

- The vectors assume water and use temperature-dependent input density values.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "fluid": "water",
    "temperature_C": 20,
    "atmospheric_pressure_kPa": 101.325,
    "vapor_pressure_kPa": 2.339,
    "rho_kg_m3": 998.2,
    "static_suction_head_m": 3,
    "suction_losses_m": 1.2,
    "NPSHr_m": 3.5
  },
  "expected_outputs": {
    "NPSHa_m": 11.911964,
    "margin_m": 8.411964
  },
  "reference_data": {
    "vapor_pressure_20C_kPa": 2.339,
    "atmospheric_pressure_standard_kPa": 101.325,
    "standard_gravity_m_s2": 9.80665,
    "source_convention": "Water vapor-pressure and standard-atmospheric-pressure values are widely tabulated standard values; standard gravity is the widely tabulated standard value."
  },
  "working": "Pressure difference = (101.325 - 2.339) kPa = 98.986 kPa = 98,986 Pa. Pressure head = 98,986 / (998.2 x 9.80665) = 98,986 / 9,788.99803 = 10.111964 m. NPSHa = 10.111964 + 3.000 - 1.200 = 11.911964 m. Margin = 11.911964 - 3.500 = 8.411964 m."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

An extreme but numerically representable input combination produces an NPSHa above the IEEE-754 binary64 finite range during addition, yielding +infinity unless the instrument validates magnitudes first. The convention probe also exposes a potentially serious 6 m error if suction lift is entered with the wrong sign.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/npsh-available-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/npsh-available-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/npsh-available-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-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`