Fire protection · calculator
Fire Pump Curve Calculator: Rated, Churn & Overload Points
Build a screening envelope for rated, churn, and 150% overload fire-pump curve points.
Method record
What this calculator measures
A centrifugal fire pump is evaluated across its curve. Excessive churn can overpressure the system, while inadequate overload pressure limits reserve flow capacity.
0 GPM ≤ 140% pressure; 100% flow at rated pressure; 150% flow ≥ 65% pressure Use it correctly
Calculation steps
- Use net pump pressure, not raw discharge gauge pressure.
- Compare the certified curve with all three points.
- Confirm suction conditions and system pressure ratings.
Applicability
Use the model within its limits
Verify the adopted NFPA 20 edition, listing, certified curve, acceptance data, component ratings, and AHJ requirements.
What this result represents
- System
- Fire protection
- Formula
- 0 GPM ≤ 140% pressure; 100% flow at rated pressure; 150% flow ≥ 65% pressure
- Review
- Verify safety-sensitive work with qualified guidance.
Worked Field Example
Worked Example: NFPA 20 Fire Pump Acceptance Verification
Field Scenario: Evaluating an annual flow test for a stationary electric fire pump rated for 750 GPM at 100 PSI net boost.
Given Input Parameters
Step-by-Step Mathematical Solution
- Point 1 (Churn / 0% Flow): Net pressure must not exceed 140% of rated pressure → Maximum 140 PSI (typical range 110–125 PSI).
- Point 2 (100% Rated Flow): At 750 GPM, net pressure must deliver at least 100% of rating → Minimum 100 PSI.
- Point 3 (150% Peak Flow): At 1,125 GPM (750 × 1.5), net pressure must deliver at least 65% of rating → Minimum 65 PSI.
Acceptance criteria: Churn ≤ 140 PSI; 750 GPM ≥ 100 PSI; 1,125 GPM ≥ 65 PSI.
Professional Guidance: Net pressure represents pump discharge gauge pressure minus suction gauge pressure.
Engineering FAQs
Frequently Asked Questions
What are the three mandatory test points defined by NFPA 20 for fire pumps?
NFPA 20 mandates three benchmark points on every stationary fire pump performance curve: Churn (shutoff / 0% flow), Rated Capacity (100% flow), and Peak Capacity (150% rated flow).
What causes a fire pump to fail its annual flow test?
Common causes include worn impeller wear rings, cavitation erosion, partially closed suction control valves, suction line blockage, or municipal supply pressure degradation during peak hours.
What is the maximum allowable pressure drop across a fire pump curve?
The curve must be relatively flat: pressure at 150% flow cannot fall below 65% of rated pressure, and shutoff (churn) pressure cannot exceed 140% of rated pressure to protect sprinkler piping and fittings from overpressurization.