Water Source, Pumping, Filtration and Fertigation Equipment
What the exam tests here
Head-unit competence: measuring source discharge, matching the pump to the system, choosing the right filter, and injecting fertilizer safely and accurately.
Core rules
- Measure discharge before designing: bucket and stopwatch for small flows, V-notch weir or flume for open channels.
- Pump total head = suction lift + delivery lift + friction losses in pipes and fittings + operating pressure head. 1 kg/cm² ≈ 10 m of head; 1 hp ≈ 0.746 kW.
- Centrifugal pumps have a practical suction lift limit of about 6–7 m; deeper sources need a submersible pump.
- Filters: sand media for pond or canal water carrying organic load; screen (120–200 mesh) or disc (100–150 micron) for clean borewell water. Backwash sand filters when the pressure difference reaches 0.5–0.7 bar.
- Fertigation: venturi (cheap, 20–30% pressure loss), bypass tank, or positive-displacement pump (most accurate). Inject upstream of the filter and flush with clean water for 15–20 minutes afterwards.
Worked example
System flow 25 m³/h, total head 30 m, pump efficiency 60%. Power = 9.81 × Q(m³/s) × H ÷ η = 9.81 × 0.00694 × 30 ÷ 0.6 = 3.4 kW, that is 4.6 hp, so select a 5 hp pump. The filter must be rated above 25 m³/h: choose a 30 m³/h sand filter followed by a 130-micron screen as a safety stage.
Traps that cost marks
- Sizing the filter at exactly the system flow with no margin.
- Ignoring friction loss in the suction line.
- Injecting fertilizer downstream of the filter, so grit and precipitate reach the emitters.
- Stopping fertigation without a flush.
Quick recall
Head in metres, power in kW; sand filter for dirty water, screen or disc for clean water.