Pump Sets, Filtration, Fertigation and Automation
What the exam tests
This domain tests total dynamic head, pump selection, filter operation, fertilizer injection and basic automation logic.
Core rules and concepts
- Total dynamic head (TDH) = vertical lift + friction loss + operating pressure, all converted to metres. 1 bar ≈ 10.2 m of water head.
- The pump must be selected at the duty point where its curve meets the system curve; a pump far from duty point may run hot, cavitate or waste energy.
- Suction conditions matter: excessive suction lift or a blocked strainer can cause cavitation and low output.
- Media filters require backwashing at a set pressure difference or time; screen filters require cleaning when the pressure drop rises.
- Fertigation injects stock solution downstream of the filter and with backflow prevention. Injection rate is set from the nutrient concentration and irrigation flow.
- Automation uses controllers, solenoid valves, pressure sensors and EC/pH sensors, but manual checks are still needed.
Worked example
Water level is 30 m below ground, the outlet is 2 m above ground, friction loss is 8 m, and the system needs 2 bar at the head. Lift = 30 + 2 = 32 m. Operating pressure = 2 × 10.2 ≈ 20.4 m. TDH = 32 + 8 + 20.4 = 60.4 m. The pump must deliver the design flow at about 60 m head. If a pump rated at 45 m is installed, the system will not reach the required pressure even if the flow looks adequate at the outlet.
Traps that cost marks
- Adding pressure in bar directly to head in metres.
- Ignoring friction loss in mains and submains.
- Injecting fertilizer upstream of a filter without considering precipitation and backflow.
- Backwashing a media filter with insufficient flow.
- Trusting automation without checking EC, pH and pressure.