Hose-reel sprinklers, advanced technology for the water resource

The extensive use of the most advanced electronic and information technologies enables optimized irrigation operations to be carried out, both based on the actual needs of the crop and to achieve rational exploitation of water, a resource that is more and more valuable. Today the market offers a wide choice of reel machines for irrigation, whose features are tailored to the needs of different companies. The sprinkler’s flow rate is an essential variable as the more extensive the covered area, the more significant the overall saving of the operation

Hose-reel irrigation machines are the equipment used for spry irrigation (commonly referred to as “sprinkler”); thanks to their remarkable versatility and adaptability to different crops, land sizes, and soil deposits, they represent a viable option to fixed or semi-fixed systems. The Italian colloquial designation “big rolls” describes the large reel that is formed when the hose is progressively wound on a large spool, while the sprinkler component moves through the field. Thanks to the initial investment, low compared to fixed systems, these machines are suited to mechanize irrigation: simple to handle, they allow to handle high surfaces, require little workforce, and do not need to install fixed pipes in the field. Moreover, they can deliver water without the need for preventive filtration and are also suitable for fertigation operations. The wide choice of models on the market, with different sizes and working capacity, and the versatility of use mentioned above have ensured the huge commercial breakthrough of these machines. It is no coincidence that reel sprinklers water about a third of the 2.5 million hectares of irrigated land in Italy.

 

A bit of history…

The first self-propelled reel sprinklers were developed in France in the 1970s. Initially, they were used almost exclusively for relief irrigation on open field crops. After almost 50 years, it is estimated that more than 65,000 examples of this type are active in Italy. The most important hose-reel sprinklers manufacturers, located in Emilia Romagna, Marche, and Veneto, have acquired a high level of technical expertise, employing, among other things, agronomists, and university researchers for field experimentation. The strategy proved to be successful for acquiring significant foreign market shares and gaining worldwide leadership in the area, hence making an incredibly positive contribution to our trade balance. The most advanced models can now work at their best on all crops, both open field and not, and are able to perform precise irrigation programs to meet the needs of the crop fully, avoiding underestimation and unnecessary waste.

 

The technical evolution

Originally, hose-reel sprinklers were assembled with components not explicitly designed for the intended use: for example, polyethylene (PE) pipes had high densities, so they were too rigid to adapt well to rolling; sprinklers were designed for watering from fixed positions, therefore rather sensitive to wind drift; turbines used for hydraulic winding required high water pressures and did not always ensure a regular winding of the pipe; a series of technical factors restricted these machines to the adoption of PE pipes with a diameter not exceeding 130 mm and a maximum length of 300 meters. Moreover, the limited technical know-how of the time led to use these machines in a basically practical way rather than using them according to detailed agronomic and meteorological information. The evolution began in the 90s of the last century with the use of specific PE pipes, with diameters up to 160 mm and above all lengths up to 700 meters, which in fact accompanied models able to cover surfaces up to 10 ha per day. The improvement geared turbines and the adoption of sprinklers specifically designed for mobile use have contributed to the improvement of hose-reel sprinklers: from initial values of 10 bar pressure, it is now possible to operate even with only 5-6 bar with sprinklers, and even just 1.5 bar with sprinkler bars, all with significant savings in diesel fuel to drive the pump.

The distinguishing feature of hose-reel sprinklers is the sprinkler, that is to say, generally speaking, sprayers and spraying booms. Until 25-30 years ago, sprinklers used to rotate with shock mechanisms, generating a “bell-shaped” distribution diagram, that is to say with a significant over-distribution of water in the center of the irrigated area compared to the side areas. The adoption of the turbine has led to a remarkable improvement in distribution standards. Besides, the application of specific speed regulators of the rewinding of the pipe according to the diameter of the reel has led to a satisfactory uniformity of water distribution even over the entire length of the irrigated area. A further innovation concerned the use of the same irrigation water to cool the air coming from the turbocharger of the endothermic engine that drives the sprinkler through an exchanger. Eliminating the radiator, in addition to definitively solving the problem of its periodic cleaning, has also enabled a slight reduction in fuel consumption and a significant decrease in noise levels.

 

The main components

The most important part of the machine is the trolley with rubber wheels, on which is mounted a long-range jet sprinkler connected to a flexible polyethylene pipe. During the preparation of the watering, the piping is unrolled, which during irrigation, is then slowly rewound automatically on the reel (a horizontal axis drum) moving the machine in return. The rewinding can be hydraulic with a turbine, hydraulic with linear motor, or hydrostatic with a self-contained endothermic motor. The motor-pump unit, on the other hand, supplies the water under pressure (which on some models can even reach 10 bar). Some sprinklers are also equipped with the function of emptying the pipe by using a compressor in order to reduce the traction force required for the starting unwinding.

 

Computerized control units

However, the crucial evolution has been driven by electronic applications. For more than 25 years, most of the machines on the market have been equipped with computerized control units, which control all the parameters for complete automation of the water supply with excellent accuracy in the delivery of the flow rates. In detail, with the control unit, it is possible to time the initial and final stop of the sprinkler, set the pipe return speed, monitor the length of the unrolled pipe, control the rainfall and the remaining working time, determine different speeds on the sprinkler course, so as to be able to give specific quantities of water according to different types of soil or crops and control the closing of the solenoid valve at the end of the irrigation. In more recent times, remotely controllable control units have been introduced, which, thanks to a data SIM, enable to remotely manage all the machine parameters through a smartphone, alerting the operator by SMS if there are any anomalies in the functioning or, as it almost always happens, simply notifying him/her that the watering program has been successfully completed.

 

Selection criteria

Although the hose-reel sprinklers enable irrigation with exceptionally low depreciation rates, in principle, it is advisable to choose those that ensure a high flow rate, therefore equipped with larger diameter hoses, in order to reduce irrigation times and related costs. In fact, the increased covered area leads to lower costs, as the incidence of the workforce is significantly reduced. Considering also that the planetary water emergency is more and more up-to-date and pressing, it becomes necessary to adopt water use optimization techniques: the latest generation of computerized hose-reel sprinklers are able to achieve considerable water savings. The theme of the “water footprint” is, among other things, a recent concept developed precisely to rationalize the use of water, representing an indicator of direct and indirect consumption of freshwater to produce a specific good or service. The water footprint concerns the evaluation of environmental, social, and economic sustainability, and the resulting identification of possible strategies to reduce consumption. The overall calculation is then represented figuratively, with different colors: blue water is used for agricultural, domestic, and industrial uses, green water is the part of the rain that does not contribute to surface runoff, and finally, grey water is what is needed for the dilution of pollutants. Logically, the agricultural sector is considerably involved in all the components of the water footprint. As a consequence, the adoption of eco-sustainable irrigation techniques is crucial for waste reduction.

It is, therefore, also essential to renew the most obsolete sprinklers:  therefore, it is advisable to activate public funding for this sector, which would help to optimize the management of water resources while increasing productivity.