1. Inventory devices
Record type, model, arc, stated flow at stated pressure, count and condition. Keep sprays, rotors and drip separate unless current manufacturer data supports a compatible design.
2. Preserve a measured-flow reserve
Use measured available flow, select a transparent reserve and floor whole heads or rows. A partial head is not a capacity result.
3. Check pressure separately
Start with dynamic pressure, subtract required head pressure, elevation and measured or calculated pipe, valve and filter losses. A zone can pass flow and fail pressure.
4. Group landscape conditions
Group sun, shade, soil, slope, plant material and exposure after the hydraulic screen. Different precipitation rates demand different schedules.
5. Check layout
Follow actual manufacturer spacing and arc data. Head-to-head language is a layout starting point, not a substitute for current nozzle charts or an irrigation audit.
6. Convert rate to time
Use precipitation rate and target depth to determine runtime. Watch for runoff, reduce cycle length and allow soak time where soil intake is lower than application rate.
7. Consider pumped supply
A pump catalogue maximum is not a zone duty point. Compare one operating condition, then use TDH and the exact pump curve for full review.
8. Commission in the field
Observe coverage, pressure, leaks, valve opening and actual nozzle installation. Record changes so future diagnosis has a baseline.
Worked example
With 100 L/min measured flow, 10% reserve and 12 L/min per head, seven heads fit hydraulically by flow. At 400 kPa dynamic pressure, 210 kPa required head pressure, 50 kPa loss and 10 m rise, pressure margin is 41.93 kPa.
Sources
- USDA NRCS — Irrigation Guide, Chapter 6
- Hunter Industries — Irrigation Technical Manual
- Rain Bird — Irrigation Design Manual