NPSH Available Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Thermodynamics, Fluids & Aero

Tranche

tranche-7

Evidence ID

t7-078

Ledger rows

1

No ledger note is attached.

Review findings

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.

Formula and scope findings

• 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.

Unit assumptions

• 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.

Boundary hardening

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.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

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

{
  "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."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

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

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche7/tranche7-results.json
• BOUNDARY_HAZARD_CATALOG.json