Pump & Fan Selection — validation & limitations

What it calculates

• Pump H-Q curve fitted to YOUR shutoff head and BEP point, with the operating point solved by bisection against the system curve
• NPSH cavitation check with margin, ratio and a suction-head sensitivity chart that covers flooded suction as well as lift
• Affinity-law speed scaling (Q ∝ N, H ∝ N², P ∝ N³) and impeller-trim scaling, with a part-speed saving computed against the REAL system curve — and reported as unavailable when the part-speed pump cannot lift the static head
• Series and parallel multi-pump configuration analysis with combined H-Q curve and operating point
• Darcy-Weisbach pipe friction (Swamee-Jain explicit factor) for commercial steel, cast iron and smooth pipe
• Specific-speed (nq) classification — radial, mixed-flow, axial-mixed, axial — plus suction specific speed
• Refuses to fabricate: a pump that cannot lift the static head is reported as having NO operating point, not given a plausible one

Related standards — reference only, not implemented

• ISO 9906reference only — Design-side pump selection: H-Q operating point on a Darcy-Weisbach system curve, NPSH cavitation check, affinity-law speed and trim scaling, series/parallel multi-pump analysis and specific-speed classification. It does not implement an ISO 9906 tolerance grade.

Validation evidence — independent reference cases (1)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

• Pump duty point, shaft power, motor size and NPSH margin

  Agrees

  Source: Hydraulic Institute ANSI/HI 1.6 / ISO 9906 definitions; Karassik, Pump Handbook, ch. 2; ANSI/HI 9.6.3; HI 1.1-1.2; hand derivation

  Inputs: H0 60 m, Q_BEP 50 m3/h, H_BEP 45 m, eta_BEP 78 %, H_static 40 m; NPSH case 150 kPa abs, 80 C water, rho 972

  Quantity	Reference value	Tolerance
  Q_op (m3/h)	57.735027	1e-5 relative
  P_shaft (kW)	8.2493902	1e-5 relative
  motor requirement x1.15 (kW)	10.311738	1e-5 relative
  NPSH_a (m)	10.749508	1e-5 relative

  tests/golden/REF-pumps-duty-power-npsh.golden.test.ts

Limitations

Not checked by this tool

• The maker's certified H-Q, efficiency and NPSH curves — The curve is a two-point parabola; confirm the duty on the maker's tested curve
• Minimum continuous stable flow and temperature rise near shutoff — Only the band around BEP is screened; check the maker's minimum flow
• Water hammer and pressure surge on start, stop or valve closure — Not computed here; see the /pipeflow water-hammer panel
• Shaft seal, bearings and casing pressure rating — Check the maximum discharge pressure (shutoff + suction) against the maker's casing and seal ratings
• Solids, slurry, abrasive or gas-entrained liquids — A clean single-phase Newtonian liquid is assumed; use the maker's derating
• Pump vibration limits — Not checked; measure on site against ISO 10816-7 / ISO 20816
• Run-out (end-of-curve) power — The motor is sized at the duty point; check the shaft power at the right end of the maker's curve if the system can run out there
• Double-suction impellers in the viscosity correction — B assumes a single-suction impeller; for a double-suction pump use Q_BEP/2 (a larger correction) or the maker's viscous data