Maintenance of Micro-Irrigation Systems

Note Number: AG0137
Published: September 1994
Updated: January 2009

Blockage of emitters in micro-irrigation systems must be minimised. Replacing blocked emitters or entire laterals is expensive. Simple maintenance procedures can be followed to avoid blockages from algae, slime bacteria, organic material and clay particles.

Cleaning the filters

Pre-season, thoroughly clean all filters. Do not overlook the body or housing of the filters. Filter housings can still be contaminated with scale or sludge when only the filter mesh, disc or media is cleaned.

Sandfilters will need to be back-flushed until completely clean and then run off through the bypass until clean water is obtained. Carefully inspect self-cleaning suction screens for any failure or holes in the mesh before placing them in the water supply.

Flushing the system

Once filters are cleaned and re-assembled, flush the system by turning on the water and opening the ends of submains. Submains must be opened one at a time so that the water velocity scours the pipe of any sediment that has settled in the pipe. Close off each submain when clean water flows and open the next submain. After flushing all the submains, start to flush the laterals following a similar procedure. More than one lateral can be opened at a time but make sure a decent skirt of water flows out the end of each lateral.

Chlorination

Inject chlorine at the pump at a rate to give 500 ppm concentration throughout the system after the loose material has been flushed and all pipes closed off. Sodium hypochlorite (Hypo) is the most effective form of liquid chlorine.

When chlorine has been distributed throughout the system, shut if off for 24 hours. This gives the chlorine time to break down any scale or sludge in the piping.

Turn on the pump after 24 hours and open the ends of laterals to flush out the dispersed sediment. Open several laterals at one time. Close the ends of laterals when the water runs clear. Normal operation of the system can now begin.

Blockages will be minimised if these steps are followed, but periodic maintenance is essential to prevent a further build-up of algae, slime and clay particles.

How much sodium hypochlorite should be used?

To calculate how much chlorine should be added to your system, you will need the following information:

• Pump discharge in litre per minute.
• Pipe length (in metres) from the injection point to the furthest outlet.

Dosage rate

Sodium hypochlorite (Hypo) contains 12.5 % chlorine. Hypo has to be injected at the rate of 4 ml per litre to give a chlorine concentration of 500 ppm and at the rate of 0.08 ml per litre to give 10 ppm.

For example, if the pump discharges 150 litre per minute, 600 ml of sodium hypochlorite needs to be injected per minute to get 500 ppm of chlorine (150 litre per minute ? 4 ml per litre = 600 ml per minute).

Dosage period

Water travels at approximately one-third a metre per second through micro-irrigation systems. To ensure that the entire system is treated, divide the distance (in metres) along the piping from the injection point to the last outlet by 20. This gives the total system run time in minutes.

For example, if the distance from the pump to the last outlet is 800 metres the injection period will be 800 ? 20 = 40 minutes.

Continue pumping for approximately 2 minutes after the sodium hypochlorite injection has finished. This will make sure that chlorine is not left in contact with the pump, filter or main valves. For more details see Agriculture Notes AG0135.

Periodic maintenance

For trouble-free operation, the following three procedures should be performed regularly:

(1) Chlorinate at the rate of 10 ppm

Use the same chlorination technique as for the pre-season treatment, but change the chlorine concentration to 10 ppm. The frequency of treatment will depend on the quality of the water used.

Chlorination once a month will be enough if the water is clean, but the system will have to be chlorinated before closing it down after each irrigation if the water is dirty. No flushing is needed after treatment with 10 ppm of chlorine.

(2) Check and clean filters

Clean filters at least once every week, and in many cases more often. The frequency of cleaning depends almost entirely on the quality of the water. Some operators, whose filters are located near the pumping plant or main valve on a piped supply, clean their filters after each irrigation.

Early in the season, the amount of material caught in the filters could mislead you, but never let the period between cleaning go beyond one week. The organic matter in most water supplies can build up very rapidly with the onset of warm weather. There is a danger of filters bursting and blocking the whole system if you are caught unawares. Regular cleaning and inspection will prevent this happening.

(3) Flush submains and laterals

Submains should be flushed at least once each month if water supply is dirty, by opening the ends until clean water runs out. This prevents the build up of sediments in pipes that never drain. Laterals need flushing less regularly because much of the water drains out of the pipe when irrigation stops.

Recent developments have seen the use of herbicides for overcoming root intrusion; and pesticides for managing insect damage to trickle irrigation systems. Acid solutions (eg. hydrochloric and phosphoric) have also been used for cleaning various materials from drip lines. Further details on these procedures should be sought from local chemical dealers and irrigation equipment suppliers if the problems mentioned above are suspected.

Acknowledgements

This Agnote was developed by Bill Ashcroft. September 1994.

It was reviewed by Ian Goodwin, Future Farming Systems Research. January 2009