Fire Pump Flow Test, Plotted
Enter the three readings. Get the curve, the net pressures, and each point against its NFPA 25 criterion — including the comparison against the original acceptance test that catches a pump failing while it still technically passes.
Net pressure is discharge less suction. Enter both gauge readings for each point and the arithmetic is done below.
| Test point | Flow (gpm) | Suction (psi) | Discharge (psi) | Net |
|---|---|---|---|---|
| Churn (no flow) | 125 | |||
| 100% rated | 103 | |||
| 150% rated | 75 |
Add the original acceptance test figures (optional)
A pump can pass all three criteria and still be failing. NFPA 25 asks you to compare against the original acceptance curve — more than 5% down warrants investigation even when the pump technically passes.
Not more than 140% of rated net pressure
At least 100% of rated net pressure
At least 65% of rated net pressure
Record the readings, the gauge identification and the speed. Next year's test is only as useful as this year's numbers are trustworthy.
The three criteria, and the fourth one people skip
At churn the pump must not exceed 140% of its rated net pressure. At 100% of rated flow it must make at least 100% of rated net pressure. At 150% of rated flow it must make at least 65%. Those are the three every test sheet records, and they are the three a plotted curve makes obvious at a glance.
The fourth is the comparison against the pump's own original acceptance test. A pump can meet all three criteria every year while sliding steadily downward, and by the time it drops below a threshold the cause has usually been developing for years. More than 5% below the acceptance curve is the point at which the standard asks you to go and find out why — a worn impeller, a partially closed suction valve, an obstructed suction, or a driver not making rated speed.
Whatever you use to record it, record the gauge identification and the speed alongside the pressures. Next year's comparison is only as good as this year's numbers.
A plotting aid, not a test report. The acceptance decision belongs to the person who witnessed the test and signs for it.