Annual Flow Test With an Uncalibrated Gauge and a Backflow Preventer
A 10-story mixed-use building has a wet sprinkler system supplied through a 6-inch reduced-pressure-zone backflow preventer. The design demand at the base of the riser is 850 gpm at 60 psi. During the annual NFPA 25 flow test, the contractor reads 70 psi static and 55 psi residual at 900 gpm from the test header downstream of the backflow preventer. The gauge used for the test has a calibration sticker dated six years ago. The contractor did not perform a forward-flow test on the RPZ because 'the annual test already flowed water.' The building's fire alarm monitoring is active, and the owner has not reported any impairment. The contractor wants to close the job as passing because 900 gpm is greater than 850 gpm.
1. Evaluate the test result against the design demand. Is the supply adequate?
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The comparison must be made at the design demand, not at a higher flow. The test point is 900 gpm at 55 psi; at 850 gpm the pressure would be somewhat higher than 55 psi but still on the same supply curve. With a static of 70 psi, the curve is steep, so the pressure at 850 gpm is unlikely to reach the required 60 psi; the contractor's '900 is more than 850' argument reverses the logic. In addition, the gauge calibration is six years old and cannot be relied on. The correct conclusion is that the test is invalid and the supply is not proven adequate. Retest with a calibrated gauge, measure flow accurately, and compare the actual pressure at 850 gpm to 60 psi. If the pressure is still short, the design needs a supply upgrade, a pump, or a re-evaluation by a qualified designer.
2. What is wrong with skipping the RPZ forward-flow test, and what must be done?
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NFPA 25 requires an annual forward-flow test of the backflow prevention assembly at the system demand, not just a static or alarm test. The RPZ's friction loss and check-valve condition affect the available pressure; skipping the forward-flow test leaves the actual system demand unproven. The contractor must flow the RPZ at the required rate, record the pressure drop, and verify that the assembly opens and closes properly. If the RPZ cannot pass the required flow, it must be repaired or replaced. The annual test report should include the forward-flow results and the gauge calibration information. 'The annual test already flowed water' is not the same as a forward-flow test at demand.
3. What impairment procedures apply while the system is being retested or repaired?
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While the system is being retested or repaired, the owner must follow NYC Fire Code impairment procedures: notify the FDNY/AHJ, tag the system, and provide a fire watch or other approved mitigation if the sprinkler protection is out of service. The fire alarm monitoring company should be notified if the system is taken offline. The contractor should not leave the system in an unknown state after a failed test. Once repairs are complete, restore the system, conduct the required tests, and document the results. The owner should keep the impairment log and the final passing test report on site. A failed flow test is not a paperwork issue; it is an impairment that affects life safety until corrected.