Pumps, Filtration, Fertigation and Automation
Pumps, filters and injection
This domain tests matching a pump to head and flow, selecting screens, sand media or disc filters, and injecting fertilizer safely. It also covers basic automation: controllers, solenoid valves, sensors and backflow protection.
Core rules
- Pump power (kW) ≈ 9.81 × Q (m³/s) × H (m) ÷ efficiency; use total head including lift, friction and operating pressure.
- A centrifugal pump is selected near its best-efficiency point; throttling a badly oversized pump wastes energy.
- Filter choice depends on water source: screen for relatively clean water, sand media for organic load, disc for mixed debris; monitor differential pressure and flush.
- Fertigation needs a backflow preventer, a tank or venturi/dosing pump, and compatible fertilizers; inject acid and chlorine separately.
- Automation should fail safe: pressure switches, flow sensors and valve sequencing prevent dry running and over-irrigation.
Worked example
A pump delivers 20 m³/h against 30 m total head at 55% efficiency. Convert flow: 20 ÷ 3,600 = 0.00556 m³/s. Power = 9.81 × 0.00556 × 30 ÷ 0.55 = 2.97 kW, so select at least a 3 kW pump and check the motor margin. If the actual head is 35 m, power rises to about 3.47 kW, which may overload a 3 kW unit.
Traps
Do not use L/h directly in the kW formula; do not ignore pump efficiency or friction loss; do not inject fertilizer upstream of a filter without checking compatibility; do not omit backflow protection; do not mix calcium and phosphate fertilizers in the same tank.