Metering devices

Details Metering devices Metering devices

1999-11-24

2002-01-29

Buiz, Michael-Powell (Department: 3753)

Valves and valve actuation

With selective flow regulation

Different sized bores in valve head

C137S487500, C137S488000, C137S510000

Reexamination Certificate

active

06341760

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to improvements in metering devices, and particularly to metering devices used in agricultural and horticultural spraying devices and related application equipment.
BACKGROUND TO THE INVENTION
Sprayers are used in agriculture and horticulture for applying chemicals and/or liquid fertilisers to growing crops, and for the treatment of harvested produce.
Generally, sprayers have a series of outlets across the width of the sprayer boom. Each outlet through which liquid is passed is provided with a check valve, commonly known as an Anti Drip Check Valve, and the check valve is generally equipped with a means to attach a nozzle or applicator on the downstream side of the check valve. Check valves are provided to prevent liquid flowing from the outlets when the said liquid is below a predetermined pressure. For example, a check valve may be set up so that liquid may not pass through the valve unless the liquid is at the intended working or application pressure.
Check valves are available in various different forms. The most common type used in agricultural and horticultural sprayers comprises a sealing diaphragm maintained against a sealing face by a compressed coil spring, the spring rate, or loading of which is determined by the pressure at which the valve is required to open and the surface area of the sealing diaphragm.
In practice when the supply pressure to the sprayer boom is switched off, the pressure in the boom supply line drops and when below the level at which it exerts sufficient force to maintain the spring loaded diaphragm check valve in an open position, the valve shuts. The length of time taken for the line pressure to drop after shut off can be lengthy, and increases as higher spraying pressures are used. Given the characteristics of the spring loaded diaphragm check valve they are not generally used in high pressure sprayer applications.
In another type of check valve, a ball loaded against an annular sealing face by a coil spring is used. Ball type check valves are generally used where sprayers are operated at higher pressures, because unlike the spring loaded diaphragm check valve their sensitivity is not dependent on, or effected by, pressure acting over a large surface area to withhold the ball from the point of sealing and therefore provide outlets with a quicker shut off.
Where high spraying pressures are to be used, it is common to provide a spring loaded check valve downstream of a spring loaded diaphragm valve to facilitate quick shut off of the outlet and manufacturers of check valves as described commonly accommodate such practice by providing suitable fittings to their check valve products.
Certain crops, ground conditions, weather conditions or chemicals require different operating pressures to be used necessitating switching over from a high pressure application to a low pressure application and vice versa. This causes time delays due to the assembly and disassembly of components. There is also a risk of components being mixed up and the operator being contaminated with toxic chemical.
Passive check valves, be they diaphragm or ball valves, share a common problem. The problem is that a time delay exists between the moment at which the liquid supply is turned off at source, and the time at which the pressure in the boom drops sufficiently for the check valves to operate and so prevent the flow of liquid from the outlets. The further away from the centre of the boom a particular nozzle is, the longer is the time delay. At present, sprayers having booms of 24 meters are often used. When operating at 2.5 to 3.0 bar and depending on the spray nozzles fitted downstream of the outlet, an operator may observe a time delay of ten seconds between shutting off liquid flow, and liquid ceasing to flow through the outlets. This causes crop damage due to patches of crop being overdosed which in turn may lead to environmental damage, and is of course a waste of valuable resource. For example, a sprayer travelling at 12 km/h may travel 33 meters in the interval between the operator shutting off the flow of liquid and the outlets actually being closed off. There is a particular problem found in brassica crops when turning at headlands. This is because brassica crops are very sensitive to chemicals and at row ends and headlands some of the crop will almost inevitably be double dosed. This has led farmers to leave field headlands unplanted which represents a considerable reduction in effective land usage.
In some countries stringent environmental protection laws have been introduced to limit the application of chemicals, such as fungicides, herbicides, pesticides or fertilisers, per unit area in given time periods in order to reduce the risk of ground water being contaminated by the said chemicals. The potential liabilities, in terms of penalties, resulting from double dosing caused by inaccurate shut-off valves is therefore of prime concern to the farmer.
A further problem posed by spring operated check valves is that operating performance is governed by the accuracy of the springs fitted within them. Coil springs are manufactured in a manner whereby the spring ratings have wide tolerances. Where springs are designed to operate check valves at 1.0 bar for instance, due to the tolerance in the spring rating one check valve may not open until a pressure of 1.1 bar is reached, whilst the check valve in an adjacent outlet may open at a pressure of 0.8 bar. Clearly, in the precision application of chemicals and fertilisers this is most undesirable.
In the spraying of liquid fertilisers it is desirable to operate at low pressures. This is because higher pressures produce fine droplets in the form of a mist which may remain on the leaves of the plants and lead to burning of the crop. In order to produce large droplets, lower pressures must be used. Conventional check valves limit the lower range of operating pressures since spring operated check valves do not operate reliably below 1 bar. Whilst liquid fertiliser can be applied at 1 bar it is desirable to operate at even lower pressures.
It would therefore be desirable to provide a check valve having controllable shut-off which can be opened at low operating pressures and which has very fine tolerances on its opening and closing pressures.
Spring loaded diaphragm check valves of the type so far described pose additional problems to users. At the time the sprayer boom is folded for transport, and/or during normal transport to or from the site of spraying, any liquid remaining in the boom supply lines tends to surge, as a result of movement, which causes localised increases in internal pressure sufficient to open the check valve and thereby allow liquid to escape. Such escape can lead to unintended contact with other crops as the sprayer passes by, double dosing or worse spraying the operator or passers by who become contaminated with toxic chemical. Such escape would permit corrosive solutions to come into contact with the sprayer, and this is particularly damaging in the case where the liquid is fertiliser. It would therefore be desirable to provide a check valve which may be adjusted to open and close at any desired pressure. It Is also desirable to provide a check valve having its shut off at a pressure closely adjacent to the operating pressure of the sprayer, which pressure may vary with time, and would therefore allow the pressure in the supply to the inlet to remain at a level close to the operating pressure required when spraying is resumed. Such a feature would reduce the time taken for full operating pressure to be achieved when the operator switches a sprayer back on when re-entering a crop.
As mentioned above, generally, sprayers have a series of outlets across the width of the sprayer boom. Each outlet through which liquids are passed is generally provided with a check valve which is generally equipped with a means to attach a nozzle or applicator on the downstream side of the check valve. The nozzle or applicator distributes the flow of liquid in a manner specific to

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