Fire Pumps, Standpipes, and Private Water Mains
Domain 5: Fire Pumps, Standpipes, and Private Water Mains
This domain tests the pressure and flow envelope from the supply to the fire floor. NFPA 20 governs fire pumps, NFPA 14 governs standpipes, and NFPA 24 governs private fire mains. You must keep rated, churn, and overload points distinct.
Core rules
- A fire pump has a rated flow and pressure. At 150% of rated flow, pressure must not fall below 65% of rated pressure. At shutoff, pressure must not exceed 140% of rated pressure.
- Standpipe Class I provides 2.5-inch fire-department outlets; Class II provides 1.5-inch occupant outlets; Class III provides both. NFPA 14 sets residual pressure at the hydraulically most remote outlet.
- Private mains require correct sizing, depth, thrust restraint, hydrant placement, and flushing.
Worked example
A pump rated 1,000 gpm at 100 psi must deliver at least 65 psi at 1,500 gpm. Its shutoff pressure must not exceed 140 psi. If a field test shows 1,500 gpm at 60 psi, the pump fails the 150% criterion even if it reaches rated flow at rated pressure.
Traps
- Confusing churn pressure with 150% flow pressure.
- Treating standpipe Classes I and II as interchangeable.
- Ignoring elevation when checking residual pressure at the top outlet.
- Assuming a private main is adequate because the hydrant flowed well at ground level.