Fire Pump Field Acceptance Test Failure
A new 1,500 gpm fire pump is installed in a high-rise. The pump is rated 1,500 gpm at 110 psi. The suction comes from a 12 in city main with a static pressure of 65 psi and a residual pressure of 50 psi at 1,500 gpm. Using calibrated suction and discharge gauges, the net pump pressure is: churn 120 psi, 100% flow 108 psi, and 150% flow 78 psi. The contractor says the pump passes because the 150% pressure is above 65% of rated pressure. The owner wants to accept the pump without a flow test using the city main because the test would require discharging a large volume of water. The pump driver is electric, and the controller is new. The city main cannot supply 1,500 gpm without dropping below 20 psi residual.
1. Determine whether the pump passes at each test point under NFPA 20 acceptance criteria.
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Check each point against NFPA 20. At churn, the pressure must not exceed 140% of rated pressure: 140% of 110 psi is 154 psi, and the measured 120 psi is acceptable. At 100% of rated flow, the pump must deliver at least rated pressure: 108 psi is below the 110 psi rating, so this point fails. At 150% of rated flow, the pressure must be at least 65% of rated pressure: 65% of 110 psi is 71.5 psi, and the measured 78 psi passes. Because the 100% flow point is below rated pressure, the pump does not meet NFPA 20 acceptance criteria as a whole. The contractor’s focus on the 150% point is incomplete. Before rejecting the pump, verify gauge calibration, pump speed, impeller trim, test valve settings, and suction conditions, because any of these can affect net pressure.
2. What suction and test conditions must be verified, and what is the acceptable alternative if the city main cannot supply the test flow?
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The suction conditions must be verified at each flow point: suction pressure must remain positive and must satisfy the pump’s net positive suction head requirement. A city main that drops below 20 psi residual at 1,500 gpm is not a reliable test source and may cause cavitation or an invalid test. NFPA 20 field acceptance requires a flow test at churn, 100% flow, and 150% flow, with stable suction conditions. If the city main cannot supply the required flow, use a temporary test tank, a suction tank, or another approved alternate source. Do not accept the pump on the contractor’s statement alone. During the test, also verify that the driver is not overloaded at 150% flow, that the controller operates correctly, and that the relief valve and circulation relief are functioning. After correcting the 100% flow deficiency, repeat the complete test and document all points.