30 TECNICA gere, in verticale, il fluido pompato. Si misura convenzionalmente in metri ed è direttamente proporzionale alla pressione: più alta è la pressione, più in alto si arriva con la prevalenza. Al contrario, la portata è inversamente proporzionale alla prevalenza e rappresenta la quantità di acqua che si può muovere attraverso una pompa. Per questo motivo è misurata in litri al secondo (o al minuto) o in metri cubi/ora. Un elemento da tenere in considerazione, nella scelta della pompa, è la dimensione delle tubature: con condotte più grandi aumenta la portata della pompa ma si riduce la pressione dell’acqua, per la legge di Poiseuille. Per questo motivo, le prestazioni della pompa impiegata dovranno essere accuratamente tarate sulle caratteristiche dell’impianto di irrigazione che si vuol alimentare. and they are so variable that they significantly affect the pump character-istics needed to achieve the best balance of efficiency, performance, and cost optimization. To sum-marize, the basic specifications to look at are three: pressure, flow rate, and head. Basically, pressure indicates the force with which the water is pushed out of the pump and conditions the distance to which the liquid can be delivered and the ability to sprinkle irrigation over large areas. It is measured in Bars. Head means the height to which the pumped fluid can be pushed vertically. It is convention-ally measured in meters and is directly proportional to pressure: the higher the pressure, the higher the head goes. In contrast, the flow rate is inversely proportional to the head and represents the amount of water that can move through a pump. That is why it is measured in liters per second (or minute) or cubic meters/hour. One factor to consider when choosing a pump is the size of the piping: with larg-er pipelines, the pump's flow rate increases, but the water pressure is reduced due to Poiseuille's law. For this reason, the performance of the pump used should be carefully calibrated to the characteristics of the irrigation establishment to be supplied. Irrigation methods and specific demands. A quick list helps to understand how much the working conditions of irrigation pumps can vary. The most common irrigation systems are sprinklers (sprin-klers or rotors) or drip (hose or micro-irrigation), either surface or underground, but pumps with piv-ots and rangers are also used in greenhouse irrigation, in draining water from ditches or ponds, and sometimes in flood irrigation. Another variable is the power system, ranging from the diesel engine (pump sets or motor pumps) to the tractor via power take-off or even the electric motor. Typically, the greatest demands in terms of pressure and head are with sprinklers, while drip irrigation needs ample flow but modest pressures. In the former case, 10 Bars can be reached, with transport lengths of up to 700 meters, while for hose systems, 3 to 5 Bars of pressure are sufficient, but with flow rates above 4 thousand liters per minute. The same applies to transfer pumps, that is, those used to draw water from reservoirs and transfer it to tanks or cisterns for transport. "For a good pump calibration, it is essential to take into account the establishment's operating parameters: type of irrigation, length to be covered, diameter of the pipes," explains Emanuele Mattiolo, from Padua, owner of an artisan company that makes pump units on a contract basis. Sustainability strategies "In the same way," adds the young mechanic, "it is important to calibrate the engine in relation to the size of the pump and the performance required of it. In other words, a balance is sought between the characteristics of the establishment being powered and the tools to power it: hydraulic pump on the one hand, the motor that drives it on the other. Both efficiency and cost depend on this, and not least, the environmental sustainability of the irrigation cycle. "In the case of the engine, size, number of cylinders, and power output affect not only the pump performance but also the fuel consumption. Using a powerplant that is too small results in higher diesel use and earlier wear TECNICA La meccanica agricola è ormai completamente globalizzata, ma, ciò nonostante, l’irrigazione resta una faccenda prettamente italiana, perlomeno nei sistemi di alimentazione. È infatti prodotta lungo lo “stivale” la larghissima parte delle pompe centrifughe utilizzate in irrigazione, mentre in altri ambiti, vedi gestione dei reflui e depurazione, si è assistito a una penetrazione di marchi stranieri, principalmente tedeschi. Nel mondo delle centrifughe, invece, vuoi per la semplicità costruttiva vuoi per la necessità di adattarsi a requisiti che sono spesso più regionali che nazionali, i marchi italiani sono predominanti Italian job Agricultural mechanics is now completely globalized, but irrigation remains a purely Italian affair, at least in its power systems. The very large proportion of centrifugal pumps used in irrigation is, in fact, produced in Italy, while in other areas, see wastewater management and purification, there has been a penetration of foreign brands, mainly German. In the centrifuge world, on the other hand, whether due to the simplicity of construction or the need to adapt to requirements that are often more regional than national, Italian brands predominate. Italian job Motopompa con pescante idraulico, adatto a recuperare acqua da fossi e stagni Motor pump with hydraulic draft, suitable for retrieving water from ditches and ponds
RkJQdWJsaXNoZXIy NTY4ODI=