Information on the mechanization of agriculture, gardening, components and multifunctionality.

Open field irrigation pumps

Modern agricultural practice often uses irrigation as a fundamental means of crop production. The related systems are based on the use of pumps. Their design differs according to the mode of adquation and the specifics of the circuits in which they are installed

by Lavinia Eleonora Galli
March - April 2023 | Back

The constantly growing world population requires a corresponding increase in food production to be met by the primary sector. Mechanization, together with progressive seed selection and the application of fertilizers and plant protection products (still intending to increase sustainability), has led to tangible improvements in yields, sometimes even with the possibility of performing two or more production cycles in the same growing season. Along with a proper supply of nutrients, one of the primary conditions for being able to achieve the best results concerns adequate water management at the various stages of the crop cycle, capable of providing for the needs of the crop and compensating for losses (through evapotranspiration, runoff, percolation, etc.). This is provided, whenever necessary, by irrigation.

Irrigation as a key to productivity. There are many different watering modes, ranging from outdated practices, such as drip irrigation, to more advanced ones involving micro-drippers, with a focus on precision distribution.

Most irrigation systems rely on the pressure that is either already held or given to the flow of water to reach the entire area of the affected plots adequately. Such pressure may be of natural origin if it is possible to harness gravity's force through technical solutions capable of moving the water mass within the irrigation system. Moreover, in most cases, the drawdown is from canals, wells, etc.,  where the water surface is at a lower elevation than that of the field, so it is necessary to overcome the relative head using a pump coupled with a power generator, which can compensate for the gradient.

Pump types. Irrigation pumps can be classified by the mode of coupling with the power generator and by their main technical characteristics. More specifically, some models work at a fixed point, and vice versa models are driven through the tractor's PTO, thus mobile. Stationary pumps can be horizontal-axis and vertical-axis.

The latter type is more suitable for draining water from deep wells equipped with small-section pipelines. As they work wholly submerged inside the wells, they cannot, in fact, be driven by endothermic thrusters but only by an electric motor.

As a general rule, pumps rely on different operation principles to take a fluid and put it under pressure. Diaphragm, gear-driven positive displacement, and centrifugal-type pumps are available.

The most suitable models for irrigation are the centrifugal ones:   water enters through the suction line (preceded by a filter to remove any solids) and is set in motion by a vane impeller, which conveys it to the outlet by increasing flow pressure.

Basically, pump performance is determined by flow rate and pressure, described by typical flow-pressure curves.   In fact, to correctly size a pump for an irrigation system, the structural characteristics of the system, the length and diameter of the pipelines, the number of branches and elbows, etc., must be taken into account. 

Materials. High speeds, pressures and the mechanical action of water inside the pumps make the latter particularly vulnerable to wear and tear. Water has a significant corrosive power that can be counterbalanced by making pumps from materials resistant to wear and corrosion. Among these, the most widely used are steel, aluminum and brass, which should be combined with appropriate construction features such as thicknesses and dimensions to maximize pumps efficiency while limiting wear and tear. Painting the components with specific anti-corrosive products can also positively affect the pump's operating life. The use of stronger, higher-performance construction materials and any ancillary treatments can result in a price increase that will be amortized through the increased service life of the pumps.

Fixed-point pumps. They are part of structured systems, such as those for sprinkling and micro-irrigation, for typically recurring use.

They are operated with either an electric or endothermic motor, with powers ranging from 20-30 to 100 Hp. Connecting multiple units in series and/or parallel is also possible to increase pumping capacity. For proper pump operation, one or more filters must be placed upstream of the system to prevent occlusions or malfunctions.

Pumps driven via the tractor's PTO. They can be easily transported to where they are needed, for example, to make up for a malfunction of the main pump or rescue watering. The connection methods between pump and tractor vary according to the overall dimensions: smaller capacity models are usually connected directly to the splined male of the pdp, while larger ones use a cardan shaft. The latter must be in perfect working condition, including, obviously, its plastic protection. This solution is seldom selected to operate structured systems, while it is very effective for gravitational irrigation systems, such as submersion, creep and infiltration. In these cases, in fact, long pipes, joints or nozzles are not used:  watering is done by distributing water at atmospheric pressure directly on the field's surface.

Wheeled diesel engine pumps

A category that can be considered "intermediate" between pumps working at a fixed point and mobile pumps in direct coupling to the tractor is the wheeled pumps, which can be driven directly by an endothermic engine (often diesel type) or through a cardan shaft.

In either case, the pump is installed on a trolley equipped with wheels that allow it to be easily moved on tow. This solution advantageously combines the peculiarities of fixed-point pumps (i.e., high power and head) with the mobility of models that can be coupled to the tractor's PTO.

Safe installation of tractor-coupled pumps

The PTO shaft enables the transmission of power in mechanical form from the tractor to the operating machine. It consists of two central telescopic tubes and two universal joints at the ends, which, duly coupled to the splined spline of the tractor and the implement's motion take-up, transfer a power (drive torque per angular speed). This is a very dangerous mechanical transmission device, which must be handled with care and diligence:  to avoid very serious and even fatal accidents, a dedicated guard must completely segregate the rotating parts, usually made of plastic material, which must have good resistance to UV rays, temperature changes, moisture, chemical corrosion, etc., and must prevent accidental contact with all rotating parts.

The guard must, therefore, completely envelop the various parts of the cardan shaft and consists of a pair of telescopic tubes, two end caps, support ferrules, retaining chains (which, adequately attached to fixed parts, prevent accidental rotation of the guard in case of insufficient lubrication), warning labels and instruction booklet.


THE MOST READ of the latest edition