Irrigation System Check

Irrigation systems should be maintained regularly to ensure top performance and costs are kept down. Poorly performing systems are a financial burden for farming businesses and result in reduced pasture or crop production.

System checks

Carry out these simple checks to ensure your pressurised irrigation system is running correctly.

• Use an accurate pressure gauge to check pressures around the system. Try at the nearest point to the pump, the furthest point from the pump, and somewhere in between. Excess pressure costs money for no real gain, while low pressure reduces irrigation performance and productivity.
• Place a number of rain gauges or small containers in the paddock while the system is operating and check how even the results are. If they are within 20 per cent (+-10 per cent of the average) of each other, the uniformity is probably adequate. If the variation is more than this, the system needs a closer look by a professional.

Centre pivots

Specific issues to check for with centre pivots are:

• The pressure at the end of the system is more important than the pressure at the centre. Both Senninger Irrigation and Nelson Australia make pressure gauges designed to be installed above the sprinkler at the outer end and are available from irrigation suppliers.
• If the field is not completely flat, check the end pressure at the highest point - just a small rise can alter the pressure at the sprinklers and reduce the output and pattern.
• If tyre pressures are incorrect and vary along the system, this may alter the speed calibration and, in some cases, exacerbate wheel ruts and bogging and cause premature failure of the drive train.

Travelling irrigators

Check for issues in big gun travelling irrigators, including:

• Incorrect lane spacing should be 60–65 per cent of wetted width in still conditions and 30-50 per cent for windy conditions. Lane spacings more than this will greatly reduce distribution uniformity. Poor distribution uniformity occurs when spray applications don’t overlap sufficiently.
• Travelling gun irrigator speed variations within runs can be as much as 50 per cent which means the amount applied varies a lot from one end to the other. Reducing speed variation improves distribution uniformity. The main factors are uneven topography, increasing drag length for soft hose machines, and variations as the hose winds up for hard hose machines. Incorrect tyre pressures may also have an effect.
• The system is operating at the specified pressure so considerable savings on pumping costs can be made by ensuring the overall pressure is minimised by minimising friction losses, using adequate pipe sizes, and selecting a nozzle with minimum pressure to do the job.
• Low pressure leads to poor uniformity, so ensure travelling guns are not operating below the recommended pressure.
• Worn nozzle will apply more water than expected and alter the spray pattern. Check size and if worn replace.
• Taper nozzles produce greater wetted diameters and are better in windy conditions. Ring nozzles break up the spray trajectory causing smaller droplet sizes and reduced wetted diameters.

Spray line and other systems

Specific issues to check for with spray line systems (including solid set systems) are:

• Check sprinklers are the same brand, type, size, and are undamaged. It is common to find systems with many different makes and types of sprinklers and/or with sprinklers that have not been checked for decades.
• Check seals at hydrants, pipe connections, sprinkler pivot points and replace any that leak.
• Check above-ground pipework and replace any with leaks, cracks, splits, dents or other damage.
• For bike shift and K-line systems, ensure that spacing between positions is correct and that overlap is adequate.

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