All components of an irrigation system have to function properly to get the desired amount of water to the plants. As with other equipment systems, regular preventive maintenance should be done to keep it trouble-free and reduce breakdowns to a minimum.
Attention to some of the major problem areas should help you keep water flowing freely.
Submersible centrifugal pumps are most commonly used with a well water source. These are very trouble free. I have had one in my well for over 35 years without any problems. An exception to this is if the water contains particulates, iron or other chemicals. An occasional disassembly and cleaning may be necessary to keep water flow and pressure up. The check valve and screen should also be cleaned when the pump is apart.
The motor lead wires should be checked due to movement of the pump in the well. Contact points on the pressure switch should also be cleaned occasionally to prevent arcing and eventual burnout of the control.
In non-municipal systems, waterlogging can reduce the volume of air and cause the pump to start up frequently. The tank should be drained completely and then precharged with air to the pressure recommended by the manufacturer. This will double or triple the amount of water that is available per cycle and reduces frequent pump startup. The pressure relief valve on the hot water tank should also be checked to see if it is working properly.
The water pipe system should be checked for leaks and weak spots. Clamps on polyethylene pipe should be tightened as these tend to loosen over time. One drop/second will waste 113 gallon/month.
Chemicals in the water can coat the inside of the pipe and fittings increasing friction loss and decreasing flow. A common problem that growers face is low flow due to too small a pipe size. For example, at a flow rate of 8 gallons/min, the friction loss in 100' of ¾" poly pipe with fittings is over 6 psi whereas if the pipe were 1" diameter, the loss would be less than 2 psi. Higher pressure can also be maintained by feeding the center of long pipes, such as the dripper lines in a long bed.
Pressure gauges can be a grower's best friend. They should be placed in strategic locations to observe the system pressure. Variations over time can help to indicate the presence of a problem.
Filters are an important part of all watering systems. Particulate or organic matter that gets into the piping can clog valves, nozzles and emitters. Screen and disc filters should be cleaned by either manually or automatically backflushing. Sand filters can be backwashed by reversing flow of water through the filter media so that contaminates are suspended in the water and drained off. Scheduling of filter cleaning can be done based on the pressure difference between the inlet and outlet using a pressure gauge. For example, screen filters are usually cleaned when the difference reaches to 3-5 psi.
Electric solenoid valves are used to automate irrigations systems. Besides dirt that can be trapped under the washer or in the valve mechanism, dust and dirt can also affect the operation of the plunger in the solenoid. This should be disassembled and cleaned with a solvent. In manual valves, the packing nut around the stem may have to be tightened occasionally or the valve seat replaced.
Controller or time clock
Dust and moisture is also the enemy of the control unit. Contact cleaner or a business cart will usually clean any open contact points. The microswitches used in time clocks have a limited life. It is best to have a couple of spares on hand to keep the system operating.
Overhead or high pressure sprinkler systems are generally trouble free if good filtration is used. If a nozzle becomes clogged, the obstruction should be blown out with compressed air rather than inserting a piece of wire that can damage the orifice.
Sprinkler bearing surfaces are water lubricated and should not be oiled. Oil can soften the rubber gasket and affect the rotation of the head.
Too high or low a nozzle pressure can affect the head movement and uniformity of water distribution. The nozzle pressure can be measured with a Pitot tube and gauge placed against the nozzle opening.
Distribution of the water from an overhead system can be fairly uniform by careful selection and spacing of the nozzles. System uniformity can be checked by placing cans or cups on a grid throughout the plant canopy. Check on the water in each container after operating the system for a period of time.
Filtration maintenance is more important with drip systems as the emitter openings are very small. Finer filtration is needed, usually an 80 – 140 mesh depending on the type of emitter. Flow meters or pressure gauges will indicate a problem.
Emitters should be inspected frequently to see that they are operating properly. Flow rate should be measured. Wide variations are indicative of plugging or water supply problems. A general decrease may be the first symptom of biological or chemical clogging.
Submains and laterals should be flushed manually several times a year. Open the ends of the lines while the system is operating and allow the water to run until it is clean.
Irrigation system can greatly reduce the labor and cost of watering plants. Preventive maintenance can help to limit potential problems before they become actual problems that can affect the operation of the system. Set a regular schedule to do this task.John W. Bartok, Jr.
Extension Professor Emeritus and Agricultural Engineer
NRME Department, University of Connecticut, Storrs CT 06269-4087