PLANT SPRAYING APPARATUS AND METHOD

Abstract: An apparatus and method for plant spraying are disclosed. Liquid plant spray is pumped at high pressure through one or more atomisers (28) to produce a mist having a small droplet size, i.e. between 5 and 60 microns. The spray may be pumped to the atomisers through a hose (24) of nylon or other material which induces an electrostatic charge in the droplets.

Description: PLANT SPRAYING APPARATUS AND METHOD FIELD OF THE INVENTION This invention relates to a spraying apparatus particularly but not necessarily exclusively for spraying plants with fungicide, insecticide and the like. DESCRIPTION OF THE PRIOR ART Conventional plant sprayers of one kind comprise a motor driven centrifugal blower which blows air through a flexible pipe of relatively large bore (i.e. of the order of 50 mm diameter). Liquid insecticide is led to the flexible pipe through a feed pipe which is connected to a tank for holding the insecticide. The insecticide is fed through the feed pipe either by gravity, by putting the tank under the low air pressure generated by the blower, by venturi effect or by a combination of these. As the liquid enters the flexible pipe it forms into droplets which are entrained in the air stream. Typically the size of the droplets emitted from a conventional plant sprayer is of the order of 250 to 400 microns. It is a disadvantage of droplets of this size that there is a lot of wastage of the spray. The reason for this is that when the droplets are deposited on the plant they have a marked tendency to coalesce into larger drops which merely run off the plant under gravity and are wasted. Furthermore the conventional sprayers of the kind referred to above are relatively slow in operation as the spray which they emit covers a relatively small area in each pass of the sprayer. In another kind of plant sprayer large drops of the liquid insecticide are dropped onto a spinning disc and become dissociated into droplets of small size. The output of spinning disc sprayers in however limited. OB JECT OF THE INVENTION It is an object of the invention to provide a sprayer which distributes the spray over a crop in a more cost-effective manner; or at least to offer the public the choice of a sprayer of novel design. SUMMARY OF THE INVENTION According to the invention plant spraying apparatus comprises at least one atomiser and means to pump liquid plant spray through the atomiser at high pressure, the atomiser being such that the plant spray pumped therethrough emerges as a mist the average droplet size of which is not greater than 100 microns. Further according to the invention a method of plant spraying includes the step of pumping a liquid plant spray through an atomiser under high pressure to form a mist the average droplet size of which is not greater than 100 microns. Liquid plant sprays include fungicides, insecticides, herbicides and the like but are not necessarily limited thereto. "High pressure" as used herein means pressure which is high enough to cause a plant spray pumped through an atomiser of orifice size between .18 mm and .60 mm diameter to emerge as a mist having a droplet size of between 5 and 100 microns. An atomiser with an orifice size of less than about .18 mm would probably be too expensive except for special purposes and equally a pump required to pump at a pressure high enough to produce droplets smaller than 5 microns would be too expensive to be commercially useful for ordinary plant spraying work. It is envisaged that the apparatus of the invention will include a pump which will operate at a pressure of about 130 bar but it is believed that, to be useful for ordinary plant spraying, the minimum pressure at which the pump should be capable of operating under ordinary conditions should be about 120 bar. Under special conditions or for some purposes however, a pump operating as low as 60 bar and as high as about 200 bar might still be useful for plant spraying. The apparatus of the invention will thus operate without the use of an air stream to draw the liquid through the atomiser. Also, since the apparatus does not use air to entrain the atomised spray. According to an important aspect of the invention the apparatus includes a small bore flexible hose at least downstream of the pump. In one form the hose is of hose material such as nylon which induces an electrostatic charge in the spray. Any other suitable hose material having the same effect may of course be used and the hose may be reinforced to enable it to sustain the operating pressure. It is an important feature of the invention that droplets are formed which are substantially smaller than the droplets formed by conventional sprayers. In one aspect of the invention the average size of the droplets produced is of the order of 5 to 60 microns. However, it might be useful for some purposes to achieve an average droplet size of up to about 100 microns. Another important feature of the apparatus is that it may comprise a wand or other distribution member having a number of atomisers, i.e. at least two but even three or more atomisers. This is made possible by the efficient action of the mist in enveloping the plants to which it is directed combined with the considerably reduced quantity of plant spray which passes through each atomiser per unit time. BRIEF DESCRIPTION OF THE DRAWING The invention is further discussed with reference to the accompanying line diagram, which by way of example, shows the arrangement of components for making up a plant or crop spraying apparatus. DESCRIPTION OF EMBODIMENT OF THE INVENTION In the drawing the outlet of a tank 10 containing liquid fungicide or insecticide is connected by a low pressure pipe 12 to, for example, a triplex (i.e. three stage) plunger pump 14 driven by a directly connected petrol engine. The pump and engine may be supplied as a single unit and are not separately shown on the diagram. A high pressure pipe 16 connects the outlet of the pump 14 to a regulator valve 18 provided with a pressure gauge 20 and a by-pass line 22 for returning excess liquid to the tank. The outlet of the regulator valve 18 is connected by a flexible, reinforced, high pressure nylon hose 24 to a rigid wand or boom 26 provided with, in this case, three liquid atomisers 28. The tank 10 is a standard size tank of capacity to suit the size of the apparatus. For example, if the apparatus is intended to be carried on the back of the user the tank may have a capacity as low as 10 litres. On the other hand a tractor mounted apparatus may have a tank of 1500 litres capacity. It is important that the tank should not be too large since suspended materials in the liquid may have a tendency to settle if the liquid remains in the tank for too long after the tank is filled or if the tank is not provided with an agitator. Since the tank 10, the pump 14 and the regulator valve 18 are all fixed on a common frame (not shown) the pipes 12, 16 and 22 may be rigid or flexible as desired. The pump 14 in one working example is a Speck τ ^ pump, model #NP 12-12-130. This pump has a rated working pressure of 130 bar and the output of this apparatus was about 3 litres per minute. Whatever pump is used it must of course have a delivery capacity matched to the capabilities of the apparatus. The capacity of the pump may be as low as 1 litre per minute for a back mounted apparatus and as high as 76 litres per minute for a tractor mounted apparatus. The regulator valve in the same working example is also known per se, being a model #UL 150, also marketed by Speck™. The pressure valve controls the pressure and rate of delivery of the liquid to the atomising nozzles. The atomising nozzles may also be of commercially available type as used in airless paint spraying equipment. The nozzle size can be chosen to suit the characteristics of the liquid and the size of droplet required. The droplet size is determined at least in part by the disease or pest for which the plants are being sprayed. The orifice size of nozzles most commonly used in the present apparatus will probably be .28 mm to .58 mm diameter. In apparatus using the above mentioned model of Speck pump operating at 130 bar as measured on the pressure gauge the average droplet size of a mist produced by pumping a liquid insecticide through a wand with three nozzles of .38 mm orifice size was determined to be 40 microns. The test comprised passing a glass microscope slide through the mist and determining the average size of the droplets which adhered to the glass. As already mentioned a hand held wand may comprise two, three or even more atomising nozzles. On the other hand a tractor mounted boom may comprise as many as thirty five atomising nozzles. It is of considerable benefit if the atomising nozzles are of tungsten carbide or other material which is resistant to the abrasion of solids suspended in the liquid. One advantage of the apparatus is believed to be that such solids tend to be broken up as they pass through the high pressure filters with which such nozzles are provided. Filters of this kind are commonly of stainless steel gauze and again are well known in airless paint spraying equipment. It is believed that the use of a nylon hose in combination with the high pressure and velocity of the liquid through the hose imparts a static charge to the mist droplets which causes the droplets to be attracted by the plants at which the spray is directed. This reduces wastage. Another factor which is believed to reduce wastage is that there is less tendency for the droplets to agglomerate in the air and, being so finely divided, eddies or swirls occur in the spray which increase the efficiency of the distribution of the droplets over the plants. Yet another factor which may contribute to the efficiency of the apparatus, still associated with the small droplet size, is that the fine mist created by the sprayer causes a sudden increase in humidity around the plant and also a rapid reduction in the humidity as the mist is dispersed. It is possible that this rapid change in humidity is beneficial for flowering and pollination. Because of the efficiency of the distribution of the mist over the plants the time taken to spray a given crop is very considerably reduced and moreover the quantity of liquid used is considerably diminished. It is not intended that the scope of a patent granted in pursuance of the application of which this specification forms a part should exclude modifications and/or improvements to the embodiments described and/or illustrated which are within the spirit of the invention as defined herein or be limited by details of such embodiments further than is necessary to distinguish the invention from the prior art.

Claims: Claims 1. Plant spraying apparatus comprising at least one atomiser (28) and means to pump liquid plant spray through the atomiser at high pressure, the atomiser being such that the plant spray pumped therethrough emerges as a mist the average droplet size of which is not greater than 100 microns. 10 2. Apparatus according to claim 1, including a pump (14) for pumping the liquid plant spray to the atomiser at a pressure of not less than 60 bar. JfJ 3. Apparatus according to claim 1 or claim 2, including a pump (14) for pumping the liquid plant spray to the atomiser at a pressure of between 60 bar and 200 bar. 4. 20 Apparatus according to any one of claims 1 to 3, in which the average droplet size is between 5 and 60 microns. 5. Apparatus according to any one of claims 1 to 4, in which the atomiser (28) has an 25 orifice the diameter of which is between .18 mm and .60 mm. 6. Apparatus according to any one of claims 1 to 5, in which the liquid plant spray is pumped to the atomiser through a pipe (24) which causes an electrostatic charge to be 30 present in the mist. 7. Apparatus according to any one of claims 1 to 6, including a rigid pipe (26) through which the liquid plant spray can be pumped to two or more said atomisers mounted 35 thereon. 8. A method of plant spraying includes the step of pumping a liquid plant spray through an atomiser (28) under high pressure to form a mist the average droplet size of which is not greater than 100 microns. 9. A method according to claim 8, in which the liquid plant spray is pumped to the atomiser at a pressure of not less than 60 bar. 10. A method according to claim 8 or claim 9, in which the liquid plant spray is pumped to the atomiser at a pressure of between 60 bar and 200 bar. 11. A method according to any one of claims 8 to 10, in which the average droplet size is between 5 and 60 microns. 12. A method according to any one ' of claims 8 to 11, in which the atomiser has an orifice the diameter of which is between .18 mm and .60 mm. 13. A method according to any one of claims 8 to 12, in which the liquid plant spray is pumped to the atomiser through a pipe (24) which causes an electrostatic charge to be present in the mist

Inventors: HEDGMAN RONALD GORDON, HEDGMAN, RONALD, GORDON
Applicants: GRANT MICHAEL JOHN, HEDGMAN RONALD GORDON, GRANT, MICHAEL, JOHN, HEDGMAN, RONALD, GORDON
Application year: 1990
Main classification: B05D1
IPC codes: A01M7, B05B5, B05D1, F02B1