Summary of design procedures

1. The peak irrigation requirement and interval are de­termined, which in turn determines how much water must be applied and how quickly. This determines flow rate through the pipe network and pump output. Con­sideration should be given to crop and soil characteristics, and site topography.

2. Determine the discharge rate per sprinkler, based on irrigation amount and expected sprinkler spacing. In conjunction with this decision decide the nozzle size(s) and water pressure to provide the necessary discharge. Consult sprinkler performance charts to determine the optimum combination. For self-propelled machines, the run spacing and travel speed of the machine need to be ascertained, based on manufacturer's data.

3. Determine the diameter of the sprayline lateral, given the flow rate per sprinkler, the number of sprinklers, and the length of the sprayline. For self-propelled ma­chines, this decision is pre-determined by the manufacturer, to suit the performance specifications of the machine.

4. Design the network of sub-mains and mains. Consider layout or positioning of spraylines or runs, distance from proposed pump site, fittings, and so on. Deci­sions need to be made on pipe material and diameter, method of installation, and optimum balance between cost and layout. Consider the effect that layout will have on pumping duty; for instance will the pump be able to handle the pressure and flow rate when the sprayline is furthest away from the pump, compared to its nearest position? This is particularly important to sites of irregular shape or layout.

5. Select pump and associated equipment. Consult manu­facturers' performance data to help this decision.

6. Select power supply and associated equipment.

Maintenance.Apart from maintenance of the pumping station, spray irrigation systems require only routine maintenance. Blocked nozzles should be cleared, and damaged sprinkler parts replaced. Spare parts should be kept on hand.

Damage could be caused by:

• Careless handling of me equipment; sprinklers, hydrants, above ground pipes.

• Wear caused by excessive abrasive material in the water.

• Normal ageing of seals and gaskets.

• Movement of buried pipes, and subsequent failure of points of connection in particular, usually caused by inadequate initial installation.

Self-propelled machines will require more substantial rou­tine maintenance, particularly the lubrication requirements of gearboxes and bearings, but also attention to tyre pres­sures and electrical components. The owner's manual for the machine will have specific instructions.

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