The chemical method of plant protection against pests, diseases, and weeds remains the main one today and for the foreseeable future. Most often, it is implemented by spraying agricultural crops with aqueous solutions of pesticides.
The quality of spraying determines the effectiveness of the product, its application rate, and the level of environmental pollution. Therefore, the central issue in the practical use of chemical plant protection products is treatment with droplets of optimal size (the smaller, the better), which completely depends on the sprayer design.
Manufacturing a sprayer suitable for such treatment is not an easy task. However, I managed to design and build a simple cup-type directional sprayer intended to produce a monodisperse aerosol cloud from aqueous solutions of agricultural chemicals. The cloud created by the rapidly rotating cup sprayer has the shape of a twisted cone (like a vortex), with the larger base aimed at the target being sprayed. Droplets from this “vortex” reach even areas inaccessible to other types of sprayers, such as the underside of plant leaves.
The sprayer housing is a piece of polyethylene tube 140 mm long, 40 mm in outside diameter, with a wall thickness of 2 mm, and serves as a kind of frame. All components and assemblies, including the working solution tank (for spraying tall plants), are compactly mounted on and inside this housing.
There are few components and assemblies, both main and auxiliary. The main ones are the electric motor, the shaft, and the cup itself.
The electric motor is a miniature DC motor of the DPM‑20‑N1 type, powered by 27 volts, with a speed of up to 9000 rpm (motors of the DPM‑25‑N1, DPM‑30, and DPM‑35 types can also be used). An adjustable power supply for this (and similar) motor is described in the magazine “Modelist‑Konstruktor”, No. 12, 2002.
1 — cup (plastic); 2 — hemispherical nut (duralumin); 3 — shaft (steel 45, Ø8 rod); 4 — housing (polyethylene tube 40×2); 5 — bearing of the 25 series (2 pcs.); 6 — washer (St3, s2 sheet, 2 pcs.); 7 — bearing housing (duralumin, Ø36 rod); 8 — retainer (M5 screw); 9 — flexible coupling (vacuum rubber tube); 10 — DPM‑20‑N1 electric motor; 11 — front bushing (plastic); 12 — bracket for extension boom (duralumin tube Ø25…30); 13 — rivet (aluminum Ø3, 6 pcs.); 14 — dovetail-type coupling part with ridge (duralumin); 15 — dovetail-type coupling part with groove (duralumin, 2 pcs.); 16 — power plug connector (from consumer radio equipment); 17 — connector bushing; 18 — rear bushing (plastic); 19 — dovetail-type coupling part for canister; 20 — main outer tube (from a medical drip set); 21 — safety bushing; 22 — feed tube (from a medical drip set); 23 — clamp-regulator of solution flow (from a medical drip set); 24 — tank for pesticide solution (0.5 L)
The electric motor is installed inside the housing in two bushings and clamped between them. Each bushing is secured against rotation with an M3 screw. Supply voltage is fed to the motor through a plug connector taken from consumer radio equipment. The connector is mounted in a plastic bushing and attached to its end face with two M3 screws. The bushing itself is fixed at the end of the housing with two similar screws.
The shaft is made of steel, stepped, and cantilevered. Its journal is mounted in two roller bearings of the 25 series installed on opposite sides of a single duralumin housing. The bearings are clamped in their seats by steel washers, each tightened to the housing with two M2 screws. The bearing housing together with the shaft is placed inside the sprayer housing and fixed there with two M3 screws.
The motor shaft and the cantilevered shaft are connected by a tightly fitted tubular coupling made of vacuum rubber.
The cup of the sprayer deserves special attention. I came across this part by chance among various scrap materials (I do not even know from which machine or unit it originally came). But it was precisely this part that inspired me to build a cup-type sprayer. The reworking of the found part was minimal: only the bottom was cut out and a through axial hole was drilled in the stem and flange (“mushroom”).
Those who wish to build a similar sprayer will probably find it difficult to obtain a ready-made cup. It is much easier to choose separate suitable parts — a cup and a “mushroom” — bonding them with adhesive or making slots in the cup wall for the flange spokes, then carefully sealing all gaps in the slots so that the working fluid does not leak out.
The external equipment — the boom bushing and the tank for treating tall plants — is joined to the sprayer housing by dovetail-type coupling parts. For this purpose, identical grooved parts are riveted with countersunk aluminum rivets to the top and bottom of the housing. Matching ridged parts are attached to the mating units — the boom bracket and the tank: the first is riveted, while the tank is glued on. The coupling part on the tank is made slightly higher and with the outer (ridge-free) surface sloping forward (toward the cup).
The dimensions of the auxiliary parts mounted outside the housing are not critical; their shape is clear from the general assembly drawing, so there is no need to provide detailed drawings for these parts.
The particle size in the “vortex” is controlled in two ways: first, by changing the feed rate of the working fluid; second, by adjusting the supply voltage to the motor, which alters the rotation speed of the cup sprayer and breaks the liquid into droplets of different sizes.
a) version for treating tall plants; b) version for treating low-growing plants;
1 — cup-type sprayer; 2 — extension boom; 3 — working tank (plastic bottle or canister); 4 — portable power supply unit (±24 V)
The operating principle of the cup-type sprayer is as follows. The working fluid flows by gravity from the supply tank through a tube onto the inner wall of the rotating cup. There, under the action of centrifugal forces, the liquid spreads into a thin film and is forcefully thrown from the cone, breaking up at the sharp edge of the cup into fine droplets of approximately the same size. The aerosol cloud is formed most completely at a distance of 200–250 mm from the edge of the spraying cup.
In working position, the cup-type sprayer is oriented horizontally relative to the ground, but it can be installed at a small angle (about ±30°) without noticeable loss of performance.
The droplet size produced by the cup-type sprayer, depending on the feed rate of the working fluid and the cup speed, ranges from 100 microns to 2 mm. The maximum consumption of working fluid is 3 L per hectare for a 60 mm cup diameter and 9 L per hectare for a 100 mm cup diameter, which corresponds to ultra-low-volume spraying rates.
The advantage of rotating sprayers is that they are practically clog-free, contain relatively few parts, and, thanks to reliable electric motors, can be used for several years without repair.
The device is designed so that by manufacturing several such modules it is possible to automate plant spraying, providing the supply of working fluid and adjustable power, which allows the operator to stay away from the aerosol cloud containing hazardous chemicals.
The cup-type sprayer can also be successfully used for painting, spraying paints and varnishes (coatings). The device makes it possible to spray liquids with a viscosity in the range of 18 to 25 s according to the VZ‑246 viscometer at a temperature of 25 ± 10 °C.
“Modelist‑Konstruktor” No. 8’2004, A. Narvatov
Recommend to read
VOLTAGE CONVERTER
On occasion purchased a portable led flashlight in China with the battery inside. The flashlight has the ability to switch between a cluster of eight super-bright LEDs and a krypton bulb...
RECYCLING SCRAP?
Sometimes it's a shame to throw away a brand new empty tin can. However, it will be yet, but already in new quality if with a chisel to carefully cut on a cylindrical stand such Bank in...
