Apparatus Systems, Water Supply, and Pumping Operations
Apparatus Systems, Water Supply, and Pumping Operations
Many tractor-drawn aerials are quints with a pump, tank, and waterway. This domain tests the systems that support the aerial and the pump math that delivers water to the tip.
Core rules
- Know the interlocks between the aerial PTO and the pump. On some rigs the pump cannot be engaged while the aerial is out of its bed, and on others the aerial cannot be raised while pumping. Learn the sequence for your apparatus.
- Water supply options: tank-to-pump, hydrant forward lay, hydrant back lay, drafting, and relay. Each requires the correct intake and the correct valve lineup.
- Protect the pump with the relief valve or pressure governor, especially when lines are shut down and the pump is still turning.
- Pump discharge pressure = nozzle pressure + friction loss + elevation. Friction loss uses FL = C × Q² × L, with Q in hundreds of gpm and L in hundreds of feet.
- Useful coefficients: 1¾-in. hose 15.5; 2½-in. 2; 3-in. 0.8; 4-in. 0.2. Nozzle pressure is typically 50 psi for a handline smooth bore and 100 psi for a fog nozzle. Elevation adds 0.5 psi per foot of rise.
Worked example
200 ft of 1¾-in. hose, 150 gpm, 100-psi fog nozzle, level ground, no appliances. Reasoning: Q = 1.5, L = 2. FL = 15.5 × 2.25 × 2 = 69.75, call it 70 psi. EP = 100 + 70 + 0 = 170 psi. If the same line were advanced 20 ft up a stairwell, add 0.5 × 20 = 10 psi for an engine pressure of 180 psi.
Traps that cost marks
Using the 2½-in. coefficient on 1¾-in. hose; adding appliance loss that is not in the layout; forgetting elevation on an upper-floor line; ignoring the water weight and reaction load the ladder pipe adds to the tip load.