NPSH Available Calculator mechanism

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

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