Centre pivot design — also called center pivot design — combines geometry, water demand, hydraulics and machine operation. Start with the area that will actually be irrigated and the hours available to supply it. Radius alone does not select the pump, nozzles or drive package.
Centre-pivot design and mainline sizing in Tenselo
Tenselo is Australian irrigation and water-engineering software with tools for centre-pivot machine design, sprinkler packages and supply-main sizing. The workflow connects three different design questions: how much water the crop needs, how the pivot distributes that water, and how the pump and mainline deliver it.
| Task | Tool and scope | Evidence to bring |
|---|---|---|
| Design the pivot machine | IRR-006 centre-pivot design: tower and span schedule, pipe package, drive configuration, pump duty and bill of materials. | Machine layout, terrain, supply conditions and current supplier data. |
| Design the sprinkler package | IRR-028 sprinkler package: outlet flow allocation, nozzle selection, pressure checks and an outlet schedule. | Outlet spacing, operating pressures, sprinkler and regulator specifications. |
| Size the supply main | HYD-007 pipe selector: compare pipe options, velocity, friction loss and available downstream pressure. | Design flow, pipe length, elevation, fittings, starting pressure and required delivery pressure. |
See the 650 m supply-main sample at 34 L/s and 5.4 bar for a public calculator-output example and downloadable report. Its 650 m dimension is the supply-pipe length, not the pivot radius. It does not validate a complete pivot installation.
The geometry example below is a separate hypothetical calculation. For drawing and CAD requirements, use the software selection guide to assess the workflow you need. New accounts require approval; running its calculators requires authorised application access.
Define the site and operating case
Record the irrigated radius, full-circle or sector operation, crop requirement, soil intake, elevation profile and available water supply. Separate the machine length from any additional wetted radius or end-gun area. Note the hours available after allowing for maintenance and other interruptions.
NSW Department of Primary Industries and Regional Development's centre-pivot guide covers siting, soil infiltration, water requirements, pressure, power and machine-selection decisions. Treat system capacity, crop requirement, application efficiency and available operating hours as connected inputs, then check that the outer-span application rate remains within the soil's infiltration capacity.
Worked example: a 300 m irrigated radius
Assume a hypothetical full circle with a 300 m irrigated radius, no end gun, no excluded area, a net irrigation requirement of 6 mm/day, assumed application efficiency of 85%, and 20 operating hours per day. No effective rainfall or other water contribution is credited. The efficiency is an assumption, not a guaranteed system performance.
| Step | Calculation | Result |
|---|---|---|
| Irrigated area | π × 300² / 10,000 | 28.27 ha |
| Gross daily depth | 6 / 0.85 | 7.06 mm/day |
| Daily water volume | 28.2743 × 7.05882 × 10 | 1,995.84 m³/day |
| Supply flow | 1,995.8353 / 20 | 99.79 m³/h |
| Supply flow in litres per second | 99.7918 / 3.6 | 27.72 L/s |
One millimetre over one hectare is 10 m³. Keep unrounded values through the calculation. A smaller operating window requires a larger flow for the same daily volume; using a larger pump does not remove sprinkler, pressure, soil or supply constraints.
How operating hours change the required flow
Keep the same 300 m full circle, 6 mm/day net requirement and assumed 85% application efficiency. The daily volume remains 1,995.84 m³. Divide that volume by the available pumping hours to compare supply duties.
| Available pumping time | Required flow | Required flow in L/s |
|---|---|---|
| 12 hours/day | 166.32 m³/h | 46.20 L/s |
| 16 hours/day | 124.74 m³/h | 34.65 L/s |
| 20 hours/day | 99.79 m³/h | 27.72 L/s |
| 24 hours/day | 83.16 m³/h | 23.10 L/s |
Reducing the window from 20 to 16 hours increases the required flow by 25%. Recheck the water source, pump curve, pipe losses and sprinkler package at that flow. The 24-hour case assumes no downtime; it is a comparison, not an operating recommendation.
Why the outer spans need more flow
A sprinkler further from the pivot centre covers a larger ring of land. For uniform gross depth and a common revolution time, a ring from radius r1 to r2 receives the fraction (r2² − r1²) / R² of the total flow. This is an area allocation, not a nozzle-selection formula.
| Radial band | Area share | Allocated flow |
|---|---|---|
| 0–100 m | 1/9 | 3.08 L/s |
| 100–200 m | 3/9 | 9.24 L/s |
| 200–300 m | 5/9 | 15.40 L/s |
A real sprinkler package divides the area among individual outlets, with boundary and overlap treatment. Use current manufacturer charts to select nozzles at the available pressure, and check regulator requirements, wetted diameter, spacing and distribution. The geometric allocation above does not account for wind, runoff or non-uniform application.
Time to apply a selected depth
At the calculated flow, applying 10 mm gross depth across the full circle needs 28.2743 × 10 × 10 = 2,827.43 m³. Continuous pumping time is 2,827.4339 / 99.7918 = 28.33 hours.
The example requires about 28 hours 20 minutes of pumping to apply 10 mm gross depth over a full revolution at constant flow. With only 20 operating hours per day, that revolution spans more than one day.
This water-volume relationship is not a percent-timer setting. The timer also needs the machine's measured or specified full-speed revolution time and the control method. Instantaneous sprinkler application rate is a different quantity and must be checked against soil intake and surface storage.
Complete the hydraulic and machine design
- Pump duty: combine source lift, mainline and span-pipe losses, elevation changes, equipment losses and the required outlet pressure. Check the critical operating position.
- Sprinklers and regulators: use the actual outlet schedule, nozzle charts and regulator requirements. Include the end gun and booster separately if fitted.
- Machine: verify span lengths, tower locations, overhang, terrain limits, wheel/drive configuration and alignment requirements with the supplier.
- Site operation: check wheel tracks, field obstructions, soil intake, supply availability, electrical requirements and the maintenance window.
The Irrigating Agriculture design overview discusses the interaction between pipe selection, operating pressure, sprinkler packages, end guns and pump matching. These checks remain necessary after calculating a target flow.
Take the inputs to your designer
A centre-pivot design brief you can fill in
Use the two-page worksheet to record the irrigated area, crop demand, available hours, source flow, machine and sprinkler details. The second page carries the supply-main inputs, required inlet pressure and open technical checks.
Keep a source or test date beside the important inputs. Leave unknown values explicit so your designer or supplier can resolve them before selecting equipment.
Download the fillable centre-pivot design brief (PDF, 2 pages)
29 fields. Fill it in with a PDF reader or print it. The worksheet collects project information; it does not calculate or approve a design.
Inspect a supply-main calculation report
This recorded 34 L/s calculation is separate from the 27.72 L/s geometry example above. Follow its own inputs and assumptions.
Inside the sample
Follow the flow through to the remaining pressure
The report records 34 L/s through 650 m of supply main, starting at 5.4 bar. The returned PE100 option has a 175.8 mm internal bore and a calculated end pressure of 4.80 bar.
Compare that end pressure with the actual requirement at the pivot inlet. The sample leaves that requirement unspecified, so it cannot confirm operation of a particular machine.
Read the supply-main report (PDF, 1 page)
The layout was prepared for demonstration from the application result. The calculator remains provisional; this is a supply-main example, not a complete pivot design or manufacturer approval.
Use the pipe-sizing walkthrough to read the result, then connect the delivery pressure to the machine and sprinkler requirements.
Centre pivot design questions
Are centre pivot and center pivot different systems?
No. They are Australian/British and American spellings of the same irrigation-system term.
Does a 300 m machine always irrigate 28.27 ha?
Only a full circle with an effective irrigated radius of 300 m has that geometric area. Sector operation, exclusions, end-gun coverage and the actual wetted boundary change the irrigated area.
Can I choose a nozzle from the ring-flow table?
No. The table allocates total flow to broad rings. Individual nozzle selection requires outlet spacing, pressure, sprinkler and regulator data, and a distribution assessment.
Continue with the pump sizing and irrigation pipe sizing guides to connect the pivot requirement to its water supply.