Verified calculation capability

Net positive suction head Calculation Capability

NPSH available: open tank (p_atm−p_v)/ρg + z − hf, or suction flange (p_s−p_v)/ρg + v_s²/2g + z_s. Optional NPSHr margin. Not pump power, not orifice, not weir, not Q=Av, not Darcy. · Physics · Fluid

Capability ID physics.fluid.npsh · version 1.0.0

Open calculator REST API MCP Evidence Evidence JSON Review policy

Model

Flange

Flange: NPSHa = (p_s − p_v)/(ρ g) + v_s²/(2g) + z_s
Open tank: NPSHa = (p_atm − p_v)/(ρ g) + z − hf
Margin: margin = NPSHa − NPSHr

Solve modes: available · margin

Inputs / Outputs

Canonical symbols for this capability. Agent schemas remain the contract.

Symbol	Quantity	Unit	Role
`p_v`	Liquid vapor pressure in Pa absolute. User-supplied; this page is not a steam table.	—	input / output
`p`	Absolute pressure at the suction flange in Pa. Flange encoding. Do not send with tank z, hf, or p_atm.	s	input / output
`v`	Suction-flange velocity in m/s. Flange only. Default 0.	s	input / output
`z`	Elevation of the flange tap relative to the pump datum in m. Flange only. Default 0. May be negative.	s	input / output
`z`	Liquid-surface elevation above the pump datum in m. Open tank. Negative is a suction lift.	—	input / output
`hf`	Suction-line head loss in m. Open tank. Default 0. Input, not a Darcy solve.	—	input / output
`p_atm`	Absolute surface pressure in Pa. Open tank. Default 101325.	—	input / output
`NPSHr`	Required NPSH in m from the manufacturer. Optional in available; required in margin.	—	input / output
`rho`	Density in kg/m³. Default 1000.	—	input / output
`g`	Gravity in m/s². Default 9.80665.	—	input / output
`NPSHa`	—	—	output
`margin`	—	—	output
`cavitation`	—	—	output
`kind`	—	—	output
`model`	—	—	output

Assumptions / Validity

Declared scope for this capability. Do not use it outside this domain.

Assumptions

NPSHa = (p_s − p_v)/(ρ g) + v_s²/(2g) + z_s; pressures absolute; SI
Open tank: p_s=p_atm (default 101325 Pa), z_s=z−hf, v_s=0; hf is an input
Not pump power, not orifice, not weir, not Q=Av, not Darcy, not a catalog NPSHr curve, not steam p_v(T)

Not supported

pump power or affinity
orifice discharge
weir overflow
Q=Av identities
Darcy–Weisbach (hf is an input)
steam p_v(T)
manufacturer catalog curves

Example

One numerical check. The calculator page holds worked steps and FAQ.

p_v=2339 z=2 hf=0.5 → NPSHa=(101325−2339)/(1000·9.80665)+2−0.5

Open this example in the calculator

Trust

Review-policy: engine tested — automated tests, sources, version lock, and evidence published. Supplemental to CVP; not Domain Expert Review. See CVP and Review policy.

Tier: Engine tested — catalog token engine_tested
Calculation version: 1.0.0
Evidence tests: 14/14 calculation tests · golden 2/2 · boundary 7/7 · property 5/5
Engine tested: Yes
Source checked: Yes
Supplemental domain review: Not performed
Named expert review: Not performed
Version lock: Supported (409 VERSION_MISMATCH)
Artifact consistency: Build verified · 1.0.0 (workspace artifacts agree)

Production attestation: Embedded snapshot: STALE · Last attested schema matched 1.0.0 snapshot / local build · Semantic contract ✓ · Last attestation PASS · current evidence changed · re-attestation required · Public/cache ✓ · Origin ✓ · Live production status PASS (0 stale; 163 CURRENT) @ 2026-09-17T06:27:56.932Z
Semantic contract: PASS
Evidence attested at: 2026-09-17T06:27:56.176Z
Last production check: 2026-09-17T06:27:56.176Z
Public / cache: PASS
Origin: PASS

Call this capability

Human page, REST, and MCP share the same engine and calculation_version. Build verified hashes workspace artifacts only. After deploy, attest:production GETs canonical URLs twice — the public/cached view an Agent actually hits, and origin — including every /capabilities/{id} HTML page. Public Capability HTML version must match catalog before production attestation passes. Live Trust rows above fetch /.well-known/calculatorx-production-attestation.json and the output schema const. Build hashes: release integrity. That proves currently published page / engine / schema / evidence / MCP agree — not that a historical version is independently immutable. Reference Calculation Standard — Production surface contract 4/4.

Tool id: npsh
Engine: npsh
REST: POST /api/v1/calc/npsh
MCP: execute_calculation with capability_id: "physics.fluid.npsh"
Agent input schema: Canonical (MCP / Agent)
Output schema: JSON Schema (latest)
Versioned input schema: Immutable pin (1.0.0)
Versioned output schema: Immutable pin (1.0.0)

References

Human-readable sources plus CVP reference evidence classes.

Sources

Try with an agent

Inspect this capability via same-origin MCP, then call execute_calculation.

curl -sS -X POST 'https://www.calculatorx.com/mcp' \
  -H 'Content-Type: application/json' \
  -H 'MCP-Protocol-Version: 2026-07-28' \
  -H 'Mcp-Method: tools/call' \
  -H 'Mcp-Name: inspect_capability' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"inspect_capability","arguments":{"capability_id":"physics.fluid.npsh"}}}'

Inspect the trust tier and required assurance level before execution. Pin calculation_version (1.0.0) when reproducibility matters. Full protocol notes: MCP docs.