Towed and knapsack atomizers and mist-sprayers: applications in gardening
Herbicide, pesticide and fertilizer treatments on small surfaces, such as gardens and green areas equipped, require hand-worn equipment from operators. From spraying pumps to atomizers, there are many models available today and suitable for every need, often equipped with instruments and control elements that allow optimal performance of the work. The systems' greater accuracy and calibration must be combined with individual protection devices to protect the operator from the risk of getting in touch with the substances used
The main purpose of gardening mist and knapsack sprayers, made to be carried by an operator, or by small tractors, is to treat parasites and weeds, or also fertiliser treatments, on small-sized or difficult-to-reach surfaces. These machines have all in common a variable capacity tank depending on the models but always limited, where the commercial product is loaded to be distributed diluted in water. There is always a filter on the loading mouth, to hold impurities. There is then a pump, for the purpose of delivering the mixture under pressure, which can be actuated manually or by a combustion engine. There are also models with a battery powered electric pump. The mixing inside the tank is hydraulic. Sprayers carried by small tractors’ three-point hitch have tanks with a capacity from 10 to 50 times higher than the knapsack models. Mixing in those with high capacity tanks can also be of a mechanical nature. The dispensing takes place through one or more nozzles.
Sprayers
Knapsack pressure sprayers can be either shoulder pack or backpack. In the shoulder packs, the pump drive is manual. The tank is generally made of polyethylene, and its capacity varies from 5 to 10 liters. They operate at a pressure of up to 3 bar, while the distribution takes place via a flexible hose (1-1.5 meters long), and a spray gun with a brass nozzle. The presence of a pressure regulator keeps the output pressure stable from the jet, thus avoiding the swings produced by manual pumping. The pressure can be set to 1.2 or 3 bar. In this way, while obtaining a constant pressure, droplets of uniform size are dispensed. Backpack spraying pumps can be operated manually or equipped with a battery-powered electric pump. The polyethylene tank’s capacity ranges from 10 to 20 liters. The pump is either made of plastic or brass, with a hydraulic mixer. The unladen weight ranges from 3.5 to 4.5 kg depending on the models. They operate at a pressure up to 6 bar. The distribution hose has a length of 1.2-1.5 meters and a spray gun with a brass nozzle, equipped with pressure regulators. The handgrip can be equipped with a pressure gauge in it to easily read the set pressure.
In models with an electric, diaphragm or piston pump, power is supplied with a rechargeable electronically controlled battery. The hydraulic shaking system can be started from the outside with a switch. The spray gun with its brass nozzle is electrically operated. The flow rate reaches the value of one liter/min at the maximum operating pressure. The spray height reaches 6-7 meters, while the length reaches 10-12 meters. The most innovative models are equipped with a display to indicate the pressure level and the battery charge. A warning signal warns that the battery is going to running out. It is also possible to find a step indicator that helps the operator maintain a constant walking speed. A variant is represented by electrically battery powered micronizers for weed control used to distribute pure herbicides or low water volumes. They consist of a polyethylene tank (10-12 liters capacity), and a micronizer powered by gravity, which produces drops of a diameter of 200-250 micron. The micronizer may also have a weeding protection, to limit the covered area and reduce the drift.
Atomizers
The atomizers make the drops diameter smaller than 100 microns. The shoulder packs are driven by a gasoline or battery powered engine. Usually the two-stroke endothermic engines are used as they have a variable cylinder capacity, according to their use, of 40 to 75 cm3. The tank’s capacity varies from 12 to 20 liters while the unladen weight is around 12 kg. The use of booster pumps, ie pumps for boosting pressure, is intended to achieve a higher flow rate to allow treatments at certain heights. The air flow rate is between 15 and 30 m3/min, while the speed may exceed 100 m/s. The horizontal range reaches 15 meters and the jet opening angle is adjustable.
Some atomizers have the ULV kit as a standard, which allows a strong spraying of the outgoing liquid to get a targeted treatment and avoiding unnecessary and harmful waste. In other models, the ULV kit is a non-standard accessory recommended together with the booster pump. The acoustic pressure level is quite high as it is between 90 and 100 dB (A), while the vibration value is between 1.4 and 2.4 m / s2. The control elements are placed on the handgrip driving both the engine and the valves to regulate the mixture flow to be delivered (from 0.5 to 5 liters/min) with the possibility to start and stop the dispensing. In some models, it is possible to switch from liquid to powder dispenser. Another possibility that is offered is to equip them with a kit that allows switching from atomizer to blower. In the rechargeable battery models, the performance is almost the same. They are lighter and the operator works with higher comfort thanks to the lower levels of noise and vibration. The portable atomizers with a three-point hitch of small tractors have a much higher tank’s capacity as it goes from 100 to 600 liters and even more. Piston or diaphragm pumps can also be electrical battery powered.
They come with a fan that creates the air stream to lead the drops to the target. When the fan is centrifugal, it is more proper to call it a nebulizer. The pressures range from 5 to over 10 bar, while the flow rates generally exceed 20 liters/min and the distribution is provided with several nozzles.
Safety for the operator
The use of plant protection products put the operator at risk of intoxication through his skin and respiratory tract. This risk is clearly higher with the machines brought by the operator. Poisoning through the skin can be directed, due to physical contact with the pesticide, or indirect, through unsuitable clothing. It is necessary to wear gloves and suits, and even shoes resistant to permeation. As far as inhalation through the respiratory tract is concerned, it should be recalled that normal filter cloth masks do not guarantee protection, so it is necessary to wear specific wear-resistant masks. Another risk is the acoustic noise, obviously higher for atomisers with a gasoline engine as, as already noticed, the acoustic pressure level is very high. Hence the need to take the precautions required when using this equipment.
