How to perform a correct maintenance of irrigation equipment

15/10/2015

For irrigation equipment to work properly throughout the year it is essential to perform technical maintenance, especially in winter, when the irrigation season has ended, or when the frequency of irrigation has decreased, in the case of persistent species .

The truth is that a good check can avoid damage, which at the end of the day will have an important impact on yields and quality of production and, therefore, in the farmer's pocket. For this reason, it is important that those responsible for this work take this recommendation seriously and dedicate time to the task of checking that everything works well.

The idea is to reach the next irrigation season with an irrigation system in perfect working order and calibrated, in order to comply with the established program.

Although the maintenance of irrigation equipment is one of the most important activities of this period, it is not the only one. In the case that the winter rainfall is lower than normal, it is necessary to consider the performance of supplementary waterings that allow to reach the spring, when root growth begins, with a soil that has a full pond, in order that The roots of the plant have a sufficient water reserve that allows them to begin their first stages of development without difficulties.

Full maintenance

The maintenance of an irrigation equipment consists of a complete revision of all its components, that is, the pump, the filters, the valves, the matrices, the sides and the emitters.

1. Motors and pumps

Much of the irrigation equipment needs pressure provided by a pump, either with a benzine or electric motor, to operate.

The maintenance of the benzineros motors requires of a greater attention, since of her directly depends its operation and useful life. In general, the following technical specifications must be followed:

Check the oil level every 8 hours of operation.
Change engine oil every 50 hours.
Clean benzine filter every 50 hours.
Spark plug change every 100 hours.
Keep springs and control cables free of dirt.
In periods where the equipment is not used for more than 30 days, the fuel tank must be emptied.

Additionally, a constant supply of fuel must be maintained for its operation.

In electric motors, such maintenance is not required, only care should be taken to keep them clean and watch out for temperature increases and bearing noises.

In relation to pumps, almost all of those that are commercialized in Chile are of the centrifugal type, that is, they make use of the centrifugal force to push the water perpendicular to the axis of rotation of the impeller.

In the maintenance of centrifugal pumps the following indications should be considered:

Observe if there is leakage of water through the packings, impeller shaft seals and casing gaskets. The water acts as coolant and lubricant of the shaft packing, preventing its wear. Additionally, when there is a leakage of water, especially in the packings of the casing, the air intake occurs, which prevents the water from being driven.
Periodically the impeller must be checked, since excessive wear causes a decrease in the useful flow and performance. The speed with which this wear increases will depend on the quality of the water pumped. Thus, waters with a lot of sand in suspension will quickly spend the impeller, so it will be convenient to change it.
It is recommended to disassemble the drive unit at least once a year to clean and check all moving parts that may suffer wear and replace them if necessary.
To remove a pump from service, the flow and pressure regulating valve mounted on the discharge pipe must be gradually closed until the fluid circulation is completely interrupted, and the engine is then switched off.
Once the maintenance of the pump has been carried out, it is necessary to mount it perfectly on a solid foundation, in order to avoid vibrations that cause displacements of the pump or motor, with the consequent disturbances due to lack of alignment.

2. Filters

The filters are important elements in an irrigation equipment since they have the function of preventing the passage of a large quantity of impurities present in the irrigation water (algae, seeds, insects, leaves, garbage, sand, etc.). These particles can plug the holes of the emitters. For this reason it is very important its maintenance.

The filters should perform a backwash process periodically to remove the stored dirt product of normal operation. The manometers, located before and after the filters, will indicate when this work should be done. In general, the normal pressure difference before and after the gravel filters is from 1 to 3 meters, a figure that increases as they are plugged. When the difference exceeds the 6 meters it is essential to backwash.

In some cases, after the backwash, the pressure gauge at the filter outlet does not increase its reading, which may be the index of a severe seal. This forces the sand to move and perform successive backwashes.

Notwithstanding the above, once a month or more frequently if the water conditions so determine, the filter should be unclogged, the gravel deposited inside removed and water injected with a hose, causing the overflow produced by the same opening carries the particles deposited inside. This wash should be continued until the water comes out clean and the gravel looks white. The removal should be done to the bottom of the filter, so that all the volume occupied by the gravel is removed.

At the end of the season, the filters have to be dismantled in order to observe the wear of their interior walls, taking advantage of the opportunity to make an application of antirust paint. It is also necessary to check the sand. If the edges are rounded, you have to change it.

Mesh filters should also be checked and cleaned constantly. If the mesh is broken or saturated with fine particles, it must be changed. If sand is found in the gravel filter, it is possible that some filter screen is broken, so it must be renewed.

To manually clean the sand filters, you have to unscrew the lid and separate the rings, spraying water under pressure and helping with a brush. It is recommended to wash them once a year with hydrochloric acid in order to avoid calcium incrustations.

3. Valves

It is necessary to periodically clean and check the holes and membranes of the solenoid valves, as they tend to fail in the third or fourth year of operation. On the other hand, if the solenoid valve does not close well, it can be a sign of the existence of a garbage between the membrane. To do this, you must proceed to disassemble and wash it inside with a brush and clean water. When assembling the valve, the packings that have deteriorated should be replaced. In the assembly process, care must be taken to follow the reverse sequence to disassembly and keep the internal parts in their original position. Additionally, electrical connections must be checked.

In relation to the air and relief valves, it is necessary to clean and periodically check the holes and membranes, which should be changed if there is any type of problem.

4. Emitters, laterals and matrices

In the matrices, laterals and drippers tend to deposit precipitates of calcium carbonate and fine particles that pass through the filters, which have to be removed from the network to avoid seals in the emitters. The best way to avoid seals is through prevention. However, many times the early detection of this type of failure is not easy. In most cases the problem is discovered when the degree of obturation is advanced, generating that the cleanliness of emitters and conductors is of a high cost.

5. Washing the irrigation network

The physical seals, in general, can be improved with an adequate selection of filtering elements, but there are particles that nevertheless manage to be deposited in the emitters, forming aggregates of greater size. To avoid this problem, a mechanical washing of the system should be carried out periodically with pressures from 3 to 4 kg / cm2 (30 to 40 m), known as "flushing". For the latter, it is essential to have extra pressure in the irrigation equipment.

The washing must start at the head and in the main line, keeping the valves of the irrigation units closed. To do this it is convenient to install valves or screw plugs at the ends of the pipes. Once the main line has been cleaned, one should proceed to clean all the side plates one by one and then continue with the sides, making the water flow for a few minutes. As a precaution, before completely closing the end of the pipe that is being cleaned, the end of the pipe in the next sector must be partially opened, continuing the process. Thus, overpressures in the network are avoided. This type of cleaning is advisable to carry out each 2 months, depending on the quality of the water.

The chemical seals are caused by the precipitation inside the structure of substances that come in the irrigation water. The most frequent are those of calcium carbonate. This is a very low solubility salt (0.031 g / l), although at a pH close to 6 it can increase up to 100 times.

Similarly, it is essential to know the magnitude of the problem, which is achieved through a chemical analysis of irrigation water. The analysis is processed according to the Langelier index, which relates water quality to precipitation of the compounds it contains. Knowing this fact, there are two types of solution:

Preventive: Applications of permanent acid when the problem is serious.
Correctors: Acid applications in some opportunities, when the water is of better quality.

The acid must be used in all the water that crops require and that passes through the equipment. However, volumes are often too large to be injected during irrigation. For this reason, it is often resorted to applying the indicated quantity only during the last part of the irrigation, in order that the substances that are found inside the installation do not precipitate when the irrigation is finished.

The most commonly used acids are sulfuric (H2SO4) 36 N and phosphoric (H3PO4) 45N, which must be chosen according to their availability and price.

In most cases, although the Langelier index does not indicate preventive application, it is necessary to perform corrective or cleaning treatments when seals are detected. These are carried out by applying acid until achieving concentrations in the irrigation water from 1 to 2 percent. To achieve this goal, it is recommended to carry out the following step-by-step:

An acid solution at 10 percent is placed in the injector pond (first the water in the pond and then the concentrated acid).
First put the necessary water and then the concentrated acid.
The mixture is applied at very low pressure, the drippers operating with minimal expense.
The pH of the acidity of the water in the most extreme drippers is then measured with pH paper until 2 to 3 values are found, which is achieved with approximately 3 at 6 liters per hectare of acid.
The installation is kept closed for 12 hours.
A pressure cleaning is carried out as indicated above (flushing).

Occasionally, when the degree of obturation is high, it is necessary to proceed to the individual cleaning of the emitters, immersing them during 15 minutes in acids at 1 or 2 percent concentration.

In relation to other precipitates such as iron, manganese and sulfur can also clog the emitters. The preventive treatment consists in causing oxidation and precipitation before the sand filters, in order to retain the particles.

An effective method of avoiding these precipitates is to continuously apply oxidants such as sodium hypochlorite. If the pH of the water is lower than 6.5, chlorine can avoid these iron precipitates, when the concentration of iron is less than 3.5 ppm. If the pH is higher than 6.5 the precipitates are avoided with concentrations up to 1.5 ppm. The application of acids may be necessary to improve the pH. The appropriate concentration of sodium hypochlorite is calculated at 1 ppm sodium hypochlorite per 0.7 ppm iron. The reaction is very fast. In the presence of manganese, care must be taken with the application of hypochlorite, since the oxidation of this element is much slower than that of iron and the precipitates can be formed after the sand filter has been passed. When the emitters are partially sealed, acid can be applied in the manner described for the calcium carbonate fillings.

Biological seals are mainly caused by algae transported by irrigation water, or developed in the filters or outlets of the emitters. They are also caused by mucilaginous substances produced by microorganisms, mainly bacteria.

When blockages of this type occur, it is necessary to carry out cleaning treatments (correctors) analogously to that described for an acid treatment, but using high concentration biocides.

One of these compounds is chlorine, widely used in the form of sodium hypochlorite at 10 or at 12%. It has an effective control over algae and other microorganisms. When mixed with water, chlorine acquires a strong oxidizing power, although only a fraction remains in a free state with biocide action. It requires a pH between 5 and 7,5 to achieve adequate control, but optimum performance is obtained with pH between 5,5 and 6,0. The cleaning of the system consists of maintaining a concentration of free chlorine between 0.5 and 1 ppm. in the water that comes from the farthest emitter, for approximately 45 minutes. If the concentration of free chlorine is lower, the effect can even be counterproductive, since low concentrations of chlorine stimulate the rapid growth of bacteria. Doses of between 3 and 10 ppm may be necessary to achieve this condition. of total chlorine. When the pH is higher than 7,5 the free chlorine needs at the end of the emitters must be of the order of 2 to 3 ppm.

The treatments can be repeated every 6 hours. Chlorine can be applied at any time during the irrigation, although it is advisable that during the last hour chlorine does not leave the emitters. The injection must be done before the filters to avoid bacterial growths in the sands.

Calculation of the amount of chlorine: To obtain a concentration of 10 ppm (10 g / m3) and knowing that the concentration of sodium hypochlorite is 10%, 0.1 liter of hypochlorite is required per m3 of water. If it is required to treat 20 m3 of water, 2 liters of sodium hypochlorite are needed dissolved in 100 liters of water and injected into the network in the required time. The dilution in the fertilizer tank does not matter. The cubic meters to be treated are obtained by multiplying the flow rate of an emitter by the number of emitters in the soil profile and by the application time of the bioside, which must be at least 45 minutes. In general, between 1 to 1.5 liters of hypochlorite at 10% per hectare in drip is required; 6 to 7 liters in irrigation by tape spaced at 1.5 meters.

Finally, for the control of algae in water sources (wells and reservoirs) treatments with copper sulphate in doses of 0,05 to 2 ppm (0.05 to 2 g / m3 of water) are recommended. Aluminum material should not be used for its preparation since toxic compounds are formed for fish.

Source: Elmercurio.com