Fire Pump Rated / Churn / Overload Curve Check (NFPA 20)
Whether a stationary fire pump sits inside the NFPA 20 three-point envelope: the churn (no-flow) ceiling at 140% of rated pressure, and the overload floor of 65% of rated pressure at 150% of rated flow, with a pass/fail and the margin at each end of the curve. A 500 gpm at 100 psi pump must hold under 140 psi at churn and over 65 psi at 750 gpm. A flat, high-shutoff curve fails churn and drives a pressure-relief-valve requirement; a weak curve fails the overload reserve the sprinkler demand needs. A design and acceptance-check aid, not a stamped fire-pump submittal; a qualified fire-protection engineer and the AHJ govern.
Formula and source
churn_limit = 1.40 x rated_psi; overload_flow = 1.50 x rated_gpm; overload_min = 0.65 x rated_psi; churn_ok = churn <= churn_limit; overload_ok = measured >= overload_min; margins as % of rated pressure.
NFPA 20 (Standard for the Installation of Stationary Pumps for Fire Protection), 2022, by name; the 140% churn ceiling and the 65%-of-rated-at-150%-flow overload point are the listed centrifugal fire pump curve limits.
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