อัปเดต 2026-09-07

Fire Pump Sizing

NFPA 20-2022

Checks a fire pump's three-point acceptance curve (churn / rated / 150%) against NFPA 20 §4.8.6.1, verifies suction pressure per §4.16, sizes the jockey pump per §4.27, derates a diesel driver per §11.6.4, and solves the pump/system operating point against an NFPA-13 Hazen-Williams demand curve.

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The parabolic pump curve is evaluated at Q=0, Q_rated, and 1.5·Q_rated and each point is checked against the orientation-dependent envelope ratios. The fire-system demand curve H(Q) = H_residual + Δz + h_L,HW(Q) is intersected with the pump curve by bisection to find the true operating point; driver power is evaluated at the worst-case 150%-flow point using a Karassik efficiency roll-off.

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NFPA 20 curve-shape envelope

H (0) \leq 1.40 H_{r a t e d} (1.20 vertical-turbine), H (1.5 Q_{r a t e d}) \geq 0.65 H_{r a t e d}

NFPA 20-2022 §4.8.6.1.4–5; shutoff (churn) head ceiling and 150%-rated-flow head floor, both expressed as ratios of the rated point.

Hazen-Williams discharge friction loss

h_{L} = 10.67 L \frac{Q ^{1.85}}{C ^{1.85} d ^{4.87}}

NFPA 13 (2025) §28.2.2.1, SI form; builds the fire-system demand curve the pump must overcome (C ≈ 120 for unlined steel).

Required driver power at 150% rated flow

BHP = \frac{ρ g Q H}{η}_{Q = 1.5 Q_{r a t e d}}

NFPA 20 §14.2.6 three-point acceptance test; worst-case brake horsepower, derated for diesel drivers per §11.6.4 (altitude + ambient temperature).

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