Water Supply, Pumps, and Standpipe Systems
This domain tests your ability to read a water supply, place a fire pump on its curve, and handle standpipe pressure. Expect flow-test interpretation, N1.85 interpolation, pump churn and rated flow, and standpipe class and pressure limits.
Supply and flow test
A static/residual flow test establishes the supply curve. Use P = Pstatic − (Pstatic − Presidual)(Q/Qtest)^1.85 for an estimate at another flow. Available pressure must be compared with demand at the same flow and elevation.
Pumps
A fire pump adds pressure: at churn it adds shutoff head, at rated flow it adds rated head, and at 150 percent of rated flow the head is limited. The system demand point must fall below the pump curve plus supply. A pump does not create water; it shifts the operating point along the supply curve.
Standpipes
Class I has 2½ in. outlets for fire department use. Class II has 1½ in. outlets for occupant use and is limited in application. Class III has both. Pressure at the top of a standpipe must be sufficient for the nozzle, and pressure-reducing valves are required where static pressure exceeds the code threshold. Friction loss in the standpipe and hose must be included.
Worked example
Flow test: 60 psi static, 20 psi residual at 1,000 gpm. Estimate at 500 gpm: 60 − 40(0.5)^1.85 = 60 − 40(0.278) = 48.9 psi. If demand at 500 gpm is 55 psi plus 10 psi elevation, the supply is short; a pump or storage improvement is needed.
Traps
Using static pressure as available; interpolating linearly instead of using N1.85; forgetting elevation; ignoring hose and standpipe friction; assuming a pump raises pressure equally at all flows; and missing PRV requirements at high static pressure.