GB2118011A - Spraying crops - Google Patents

Abstract

A crop spraying system mounted on a vehicle comprises a liquid container (14) having a pressuring system, e.g. an air compressor 12, for forcing liquids therefrom to a number of sprayheads (18). The pressurizing system is controlled by a valve 15 in accordance with ambient temperature (to which the valve responds automatically) and the vehicle speed so that a substantially constant quantity of liquid is sprayed per unit area of ground. The liquid is delivered to the sprayheads by a gear pump (16) driven at a speed proportional to that of the vehicle. The pressure downstream of the pump operates on a piston 60 which adjusts the valve 15. <IMAGE>

Description

SPECIFICATION Spraying systems for liquids This invention relates to spraying systems for liquids and particularly, but not exclusively, to spraying systems for agricultural crops which utilise an electrostatic liquid spraying system.

In such systems a suitable liquid is sprayed on to the crops from a moving vehicle, such as an agricultural tractor, and the electrostatic spraying system minimises the quantity of liquid used as well as ensuring that the crops are thoroughly coated both on top and underneath with the liquid.

This is achieved by making the liquid impinge on a conducting surface which has an earthed field intensifying electrode mounted adjacent thereto.

When the conductive surface is electrically charged to a potential of the order of 1-20 kilovolts an electrostatic field is formed at the surface which causes the liquid droplets to atomize on hitting the surface and form electrically charged particles which are projected away from the surface and the electrode towards the surface of the crop which has, of course, earth potential.

It is an object of the present invention to provide a spraying system for liquids which will provide a substantially uniform covering of the liquid on the parts to be sprayed.

According to the present invention, a spraying system for liquids comprises liquid container means, pressurising means for the container means for forcing liquid therefrom to at least one sprayhead, the at least one sprayhead being movable over a surface and control means for controlling the pressurising means in accordance with at least one variable parameter, such as ambient temperature or the relative speed of movement between the sprayhead and the surface being sprayed, whereby a substantially constant selectable quantity of liquid is sprayed per unit area of the surface.

Preferable, the spraying system is mounted on a movable vehicle and is adapted to spray the surface over which the vehicles moves.

The pressuring means preferably comprises an air compressor which is adapted to pressurize a compressed air reservoir, the liquid container means being supplied with compressed air from the reservoir via the control means.

Preferably the control means varies the supply of compressed air in accordance with the speed of movement of the vehicle and the ambient temperature.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which FIGURE 1 is a pictorial view of an agricultural tractor having a spraying system for liquids in accordance with the invention, FIGURE 2 is a schematic arrangement of the spraying system and, FIGURE 3 is a cross-sectional view of a control system for compressed air incorporated in the system.

The spraying system is mounted on an agricultural tractor 10 and consists basically of a compressor 12, a compressed air reservoir 13, one or more containers 14 containing the liquid to be sprayed, a pump 1 6 and a number of sprayheads 1 8.

The whole system is mounted on the tractor 10 in a supporting frame 20 which also supports a boom 22 carrying the sprayheads 1 8 in a suitable spaced apart relationship.

The air compressor 12 pumps air into the reservoir 13 and a valve 1 5 such as described in our co-pending Patent Application No. 8205446 controls an air supply from the reservoir to the container 14 in accordance with the vehicle speed and ambient temperature. A suitable liquid such as a pesticide or a herbicide is contained in the container 14 and the air pressure from the reservoir forces the liquid out of the container 14 through a series of restrictors such as described in our co-pending Patent Application No. (Ref.

1398/F.1 2706).

The liquid is passed to a gear pump 1 6 which pumps the liquid to a gallery 24 and thence to a plurality of spray nozzles 1 8. The gear pump 16 is driven at a speed proportional to the speed of the tractor. Various stop valves such as the solenoid operated valves 26 are included in the system so that leakage is prevented when the system is inoperative or so that a limited number of sprayheads 1 8 can be used.

The system can thus be adjusted to spray a substantially constant predetermined quantity of liquid per unit area of ground with the tractor running at a constant speed and with ambient temperature constant.

FIGURE 3 illustrated the operation of the valve 1 5 which consists of a body 110 with an air inlet duct 52 and an air outlet duct 32. A ball 30 is urged against a seating 54 by a spring 58 so that the valve acts as a one way valve and also only allows air to pass through to the outlet duct 32 when the air pressure in the inlet duct 52 exceed a predetermined value. The end of the spring 58 abuts the end of an oil-filled bellows 1 26 which is adapted to expand when its temperature increases and thus increase the tension in the spring 58. The liquid in the container 1 4 tends to be fairly viscous and its viscosity varies with temperature.Thus as the ambient temperature increases, the viscosity of the liquid decreases, and a lower pressure of air is required to force the liquid out of the container.

The increase in tension in the spring 58 reduces the pressure of the air passing through the outlet duct 32 and into the container 14 and the system automatically adjusts itself to deliver the required quantity of liquid to the pump 1 6.

If the speed of the tractor varies, for example increases, the speed of the pump 1 6 increases.

The pressure downstream of the pump increases and this pressure is communicated to the valve 1 5. The cylindrical body 110 of the valve is connected to an end portion 42 by a series of balls 44 which are located in separate recesses formed in the surface 46 of the body 110 in a helical array, the balls 44 engaging a helical track 50 formed In the surface 48 of the end portion 42.

The outer surface of the body 110 is provided with d portion of coarse knurling or a set of fine gear teeth 134, a moveable rack 36 having similar knurling ar gear teeth being adapted to engage the knurls or teeth 134. Movement of the rack transversely of the body 110 causes rotation of the bedy whilst the end portion 42 is held stationary. The movement of the series of balls 44 ih the helical track 50 causes the body 110 to move axially relative to the érid portion 42 thus alteriiig the tension in the spring 56.

The rack is connected by suitable means, such as a piston and cylinder assembly 60, to be moveable in accordance with the pressure of the liquid downstream of the pump 16. When this pressure increases the rack 36 rotetes the body 1 10 so as to decrease the tension in the spring 68 This permits compressed air at a higher pressure to pass the ball 30 and be transmitted to the container 14 with the result that a greater quantity of liquid is forced out of the container 14 to meet the increased demand of the pump 16.

It is understood that the foregoing description of one embodiment of this invention is made by way of example only and various aspects of the spraying system may be modified or added to whilst the system remains within the scope of the invention.

Claims (2)

1. A spraying system for liquids comprising liquid container means, pressurizing means for the container means for forcing liquid therefrom to at least one sprayhead, the at least one sprayhead being movable over a surface and control means for controlling the pressurizing means in accordance with at least one variable parameter between the sprayhead and the surface whereby a substantially constant delectable quantity of liquid is sprayed per unit area of the surface.

2. A spraying system constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.