Fire Pump, Combined Standpipe, and Lower-Floor Pressure
A six-story, 78-ft hotel in Las Vegas has a combined wet standpipe and sprinkler system. The city water flow test shows 60 psi static and 1,100 gpm at 20 psi residual. The fire pump is rated 1,000 gpm at 100 psi, with a churn pressure of 120 psi and 150% flow at 65 psi. At the combined demand of 1,000 gpm, the city supply contributes 30 psi at the pump suction; the system demand at the pump discharge is 115 psi. The pump is in a ground-floor pump room with a test header. The building has Class I hose valves at each floor and a roof manifold. The owner wants to accept the pump without a flow test because the factory curve is available, and the contractor proposes to remove the pressure-reducing valves on the lower-floor standpipe outlets to 'improve flow.' A recent insurance survey noted that the lower-floor hose valve static pressure was 190 psi.
1. Is the fire pump adequate for the combined demand? Show the pressure comparison and explain what else must be verified.
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At the combined demand of 1,000 gpm, the pump adds 100 psi and the city supply contributes 30 psi at the suction, so the pump discharge pressure is about 130 psi. The system demand at the pump discharge is 115 psi, leaving about 15 psi of margin at the rated point. On paper, that is adequate for the demand point. But adequacy is not proven by the factory curve alone. The pump must be flow-tested in the field at churn, 100% rated flow, and 150% rated flow, and the results compared with the certified curve. The suction supply must be measured during the test, not assumed. The 150% point is a pump-performance check, not the system demand point; the test confirms the pump can deliver it without cavitation or excessive speed change. The acceptance decision should also confirm that the pump controller, relief valve, and sensing lines are set correctly and that the combined standpipe/sprinkler demand is still the governing demand.
2. Evaluate the proposal to remove the lower-floor pressure-reducing valves. What is the correct pressure-management approach?
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Removing the PRVs is the wrong direction. The lower-floor hose valve static pressure of 190 psi already exceeds the pressure limit for standpipe components and hose valves, and removing the PRVs would expose occupants and firefighters to even higher pressure. The correct approach is to keep or repair the PRVs, verify their setting and capacity, and confirm that each outlet stays within the allowable residual and static pressure limits. The pump churn pressure plus city static can produce roughly 180 psi at the pump discharge, and elevation and system pressure can push lower outlets above the component limit. The design must provide pressure control at the lower floors without starving the upper floors. Any change to PRVs requires engineering review, a hydraulic recalculation, and fire marshal acceptance; it is not a field modification to improve flow.
3. What acceptance and documentation steps should be completed before the owner accepts the pump and standpipe system?
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The contractor should perform a field flow test using the test header and calibrated instruments, record suction and discharge pressures at churn, 100%, and 150% of rated flow, and compare the results with the certified pump curve. The test should confirm that the pump does not exceed its maximum allowable discharge pressure and that the relief valve functions. The standpipe should be flow-tested at the hydraulically most remote outlet and at the low-elevation outlets with PRVs in place, with pressures recorded. The documentation should include the flow test report, pump curve, PRV settings, controller settings, and a statement that the combined demand is met. The owner should not accept the pump based only on the factory curve, and the contractor should not remove PRVs without a revised design and approval.