WO2009106893A1

WO2009106893A1 - Flow control device

Info

Publication number: WO2009106893A1
Application number: PCT/GB2009/050198
Authority: WO
Inventors: Michael Brady
Original assignee: Billericay Farm Services Limited
Priority date: 2008-02-26
Filing date: 2009-02-26
Publication date: 2009-09-03
Also published as: GB0803465D0; GB201014830D0; GB2470155A; GB2470155B

Abstract

A flow control device (10) for adjusting the rate of flow of a pressurised liquid. The device (10) comprises an elongate body (15) defining an inlet (11) for receiving liquid under pressure, one or more aperture (18) through which liquid may pass, and a flow path from the inlet (11) to the or each aperture (18). The device (10) includes a resilient sheath (19) mounted around the body (15) to close the or each aperture (18). The sheath(19) is expandable in response to increases in the pressure of the liquid to open the or each aperture (18) and to define an outlet (13) between the sheath (19) and the body (15). This permits the liquid to flow out of the or each aperture '(18) and be ejected from the outlet (13). The rate of flow is directly proportional to the pressure of the liquid introduced to the inlet (11), such that an increase in liquid pressure increases the size of the outlet (13), resulting in an increase in flow rate.

Description

FLOW CONTROL DEVICE

The present invention relates to a flow control device, and in particular to a flow control device which enables accurate control of the flow rate of a pressurised liquid.

The present invention is particularly well suited to use with liquid fertiliser and primarily will be described with respect thereto, but it is not limited solely to such a liquid.

To improve crop yields, fertiliser may be applied on a regular basis. The fertiliser can either be applied as a solid in the form of granules or prills, or as a liquid aqueous solution or suspension. Each form of fertiliser has respective advantages and disadvantages, and each is in common use. Liquid fertilisers in particular have the advantage of providing accurate placement as well as requiring relatively less labour to use. Further, they are not as harmful to the equipment used to deliver them as compared to other forms of fertiliser. Liquid fertilisers are applied using crop-spraying apparatus, and in large-scale agriculture are usually applied with dribble bars rather than spray nozzles. Each dribble bar generally comprises an inlet to receive the liquid fertiliser, a metering disc with variable hole size to control the rate of flow of liquid from the dribble bar, and a plurality of outlets (generally four) to direct the liquid fertiliser into streams, rather than a spray, so as to reach the soil with minimal contact with crop leaves.

The rate of application of the fertiliser is chosen to suit the needs of the crop and the condition of the soil in which the crop is being grown. The rate can be controlled in three ways - by adjusting the flow rate from the dribble bar, adjusting the width of soil covered and by adjusting the speed over the ground of the vehicle applying the fertiliser.

The vehicle's top speed is limited as the vehicles used to apply the fertiliser are often large, and are travelling over uneven ground. However, to minimise costs and time, it is desirable to keep the vehicle speed as high as possible. Further, the width of the sprayer's arms and hence the width of soil covered must be kept to an optimum to ensure adequate coverage and sufficient stability. In practice therefore, the only way of varying the fertiliser application rate over a wide range is to change the size of the metering hole in each dribble bar. This has to be done manually before application starts.

Further, with the advent of GPS technology, farmers are now able to record crop yield data metre by metre as their crop is harvested. Combined with soil analysis, the fertil iser needed for the next crop can then be determined. This gives rise to a need to vary dynamically the application rate to suit the changing soil requirements.

At present the application rate can only be varied from the cab of the vehicle by a small amount by altering the tractor speed and/or the liquid fertiliser feed pressure. If larger changes are required the dribble bars need to be reset individually. Manually resetting a large number of dribble bars by hand would be impractical, as this would take a long time, with 48 dribble bars on one vehicle being normal. The usable pressure that can be exerted through a dribble bar is generally from 1.25 to 3.5 bar (1 bar being 100 kPa). From Toricelli's law the flow rate is proportional to the square root of the pressure. This gives a flow rate maximum to minimum ratio of 1.7 to 1.

The flow rate in litres per second from an orifice is calculated by the equation 1000^*agh, where a is the area of the orifice in square metres, g is the gravitational constant 9.81 , and h is the pressure measured in metres of head. The only means of making big changes in flow rate therefore is to change a. As previously mentioned, this is done on the dribble bar manually by setting the size of the metering hole. Attempts have been made to produce a dribble bar or nozzle with pressure-dependent metering holes. These normally comprise a piston biased by a spring, the piston movement coupled to a valve which opens as the pressure is increased. These prior-art pistons suffer from several drawbacks, for example they are relatively bulky and expensive due to the number of moving parts required. The piston and valve are also liable to seize, as the use of such devices, is only intermittent. Furthermore, the liquid fertiliser only has limited lubrication properties and is corrosive to some metals, making degradation and seizure more likely. The aim of the invention is to provide a flow control device which easily adjusts the flow of a pressurised liquid such as fertiliser in a linear manner.

Therefore according to the present invention there is provided a flow control device for adjusting the rate of flow of a pressurised liquid, the device comprising:

- an elongate body defining an inlet for receiving liquid under pressure, one or more aperture through which liquid may pass, and a flow path from the inlet to the or each aperture; and

- a resilient sheath mounted around the body and closing the or each aperture, the sheath being expandable in response to increases in the pressure of the liquid to open the or each aperture and define an outlet between the sheath and the body to thereby allow the liquid to flow out of the or each aperture and be ejected from the outlet at a rate directly proportional to the pressure of the liquid introduced to the inlet, such that an increase in liquid pressure increases the size of the outlet resulting in an increase in flow rate.

The device of the present invention is primarily intended to be used to control the rate of flow of liquid fertiliser when spraying crops. Of course, the device can be adapted for use to control the flow rate of any liquid for any particular purpose where the simple adjustment of flow rate is required.

The main advantage of the present invention over the prior art devices is that the flow rate from the device is dependent on the pressure of liquid entering the device, and that an increase in liquid pressure produces a linear increase in flow rate, something that is not provided by the prior art. Figure 1 shows a graph plotting the flow rate in litres per minute versus pressure measured in bar. The solid line represents flow through a simple hole, and the dotted line represents flow through the device of the present invention. As shown here, liquid does not flow from the device of the present invention until the pressure reaches a certain threshold. Once the threshold is passed, at approximately 1.25 bar, flow begins and increases linearly with an increase in pressure. Flow through a simple hole on the other hand does not follow such a linear relationship, meaning that it is increasingly complicated to calculate flow rates accurately, and also that the upper limit of the flow rate cannot be reached without submitting the spraying apparatus to unreasonable pressures.

The present invention preferably allows a ten-to-one ratio of flow to be controlled by a three-to-one ratio of pressure. Preferably, flow rates of 0.1 to 2.5 litres per minute will be achievable; though of course depending on the use required these rates can be increases or decreased accordingly.

The body of the device is preferably substantially tubular with at least one closed end. Preferably, the top end of the body is open which acts as the inlet, and the bottom end of the body is closed. The or each aperture is preferably disposed in the side wall of the body, which side wall is at least partially surrounded by the sheath.

The device may advantageously be used in conjunction with a dribble bar having a main inlet and a plurality of nozzles as previously described, supplying streams of fertiliser to crops from the nozzles. In one embodiment of the present invention a single flow control device is provided in the dribble bar, and the outlet thereof is in communication with the nozzles. The pressurised liquid enters the body of the flow control device through the inlet and then exits through the outlet. The pressurised liquid then leaves the dribble bar through the nozzles. It has been found that four is the optimum number of nozzles, but any reasonable number can be provided.

In an alternative and more preferable embodiment, there may be provided a plurality of flow control devices disposed within a dribble bar, wherein each flow control device is in communication with a single nozzle. All of the flow control devices receive liquid from the main inlet. The pressurised liquid enters the dribble bar through the main inlet, and under pressure the liquid is supplied substantially equally to the inlets of each of the flow control devices. The liquid then exits through the outlet of each flow control device and out of the dribble bar. This embodiment has the advantage over the previously mentioned embodiment in that even if the dribble bar is tilted, for example if the crop-spraying vehicle is traversing uneven ground, the liquid will leave the outlets at a uniform rate because the flow of liquid is divided before the liquid enters the flow control devices. If a plurality of flow control devices is not provided in a dribble bar, they may be provided separately, with the body of the flow control device being preferably mounted in an outer casing.

The liquid leaves the outlet at a rate dependent on the pressure of the liquid entering the device because the size of the gap between the body section and the sheath increases in proportion as the sheath expands with an increase in pressure. Therefore, the sheath must be made out of a suitable material that expands a suitable amount under pressure, and retains its elasticity during repeated use. Further, the sheath must be relatively unreactive and if appropriate be able to withstand constant exposure to liquid fertilisers and other volatile chemicals. It has been found that silicon rubber has all of the suitable properties for use with the present invention . Specifically, it has been found that a sheath 3mm to 3.2mm thick with an internal diameter of 4.8mm to 5mm, stretched over an elongate body with a diameter of 5.8mm and having two opposed apertures 2.5mm in diameter provides the optimum results.

The device of the present invention will preferably be provided with a pump to supply the liquid under pressure to the inlet. The pressure supplied by the pump to the device can be controlled either manually or automatically. Often, a quantity of devices according to the present invention will be applied to a rig mounted on a tractor or other vehicle to apply fertiliser to a field. Each device can be controlled centrally and individually by a computer which calculates the precise amount (and therefore rate of flow) of fertiliser that must be supplied to each area of the field. These amounts and flow rates can be obtained beforehand using GPS technology and previous crop yields to draw up a complete map of each field with the specific quantities of fertiliser required for each area.

Preferably, the flow control device of the present invention will be replaceable within a dribble bar for example to allow repair or replacement. So that the invention may be better understood, but by way of example only, two embodiments thereof will now be described in detail, with reference to the accompanying drawings wherein: Figure 1 shows a graph plotting the flow rate in litres per minute against pressure measured in bar;

Figures 2a and b show vertical cross sections through a flow control device of the present invention in different flow conditions; and Figure 3 shows a schematic representation of a dribble bar in conjunction with the present invention.

Figure 1 , which has already been described above shows a graph plotting flow rate against pressure. The graph shows the linear relationship between pressure and flow which the present invention provides. Figures 2a and 2b show a device of the present invention in different flow states. In each there is shown a flow control device generally indicated 10 comprising a tubular body section 12 defining an inlet 11 and an outlet 13. The flow control device 10 is often to be used in conjunction with a device such as a dribble bar, which will be described in detail below. The tubular body section 12 is constructed from a rigid, non-reactive material such as metal or plastic. Within the body section 12 is a generally cylindrical tube 15, which is firmly fixed to the external wall thereof by connector 16 which seals the space between the outer wall of the tube 15 and the inside wall of the body section 12. The tube 15 is open at the end nearest the inlet 1 1 , and closed at the other end by end wall 17. Extending through opposite sides of the tube 15 are apertures 18. A resilient silicon rubber sheath 19 is located around a lower section of the tube 15. The sheath 19 grips the tube 15 as shown in Figure 2a and blocks the apertures 18 to prevent liquid that has entered the inlet (as represented by arrow 21 ) from passing out through the apertures 18 (as represented by arrow 20). As shown in Figure 2b, liquid entering the inlet (as represented by arrow 21 ), which is subject to a pressure in excess of a defined threshold has sufficient force to expand the sheath 19 and allows liquid to pass through the apertures 18 and flow between the sheath 19 and the wall of the tube 15 to the outlet 13 as represented by arrow 22. The size and quantity of the apertures 18 sets an upper limit for flow rate of liquid through the flow control device 10. As pressure of liquid entering the inlet increases, once a certain threshold is exceeded the sheath 19 starts to expand. The expansion of the sheath 19 increases the size of gap through which liquid can flow. When the sheath 19 tightly covers the apertures 18, the gap is closed - i.e. there is zero flow. As pressure increases so does the size of the gap and the rate of flow, up to the maximum rate possible (which is dependent on the area and quantity of apertures 18). There is a linear relationship between the flow rate and pressure at which the liquid is supplied. Increases in pressure will produce a linear increase in the flow rate, and decreases in pressure produce a decrease in flow until the pressure falls below a minimum threshold after which flow will stop altogether.

Figure 3 shows an embodiment of the present invention, wherein four flow control devices are incorporated within a dribble bar generally indicated 30. The dribble bar 30 comprises a main body 31 , a main inlet 32, and four outflow pipes 33, 34, 35, 36. Within the main body are four flow-control devices, generally indicated 37, 38, 39 and 40. These flow control devices are essentially identical to the flow control device described with reference to Figures 2a and 2b, so like parts will be given the same reference numerals in Figure 3. The difference between the flow control device in Figures 2a and 2b and that in Figure 3 is that the tubular body 12 is provided by recesses of a chamber in the main body 31. The outlets 13 on the flow control devices 37, 38, 39, 40 extend through the main body 31 to the pipes 33, 34, 35, 36 from which streams of liquid are ejected.

In use, the main inlet 32 receives pressurised liquid from a pump, which draws it from a reservoir (neither the pump nor the reservoir are shown). The liquid enters a chamber 41 within the main body 31. Liquid from the chamber 41 enters each flow control device 37, 38, 39 and 40. If the liquid pressure within the chamber 41 exceeds the threshold, then the sheaths 19 will expand and liquid will pass through the apertures 19 and down through the gap between the tubes 15 and the sheaths 19. The liquid will then pass through the outlets 13 and out of pipes 33, 34, 35 and 36. Increases in the liquid pressure will cause further expansion of the sheaths 19 and lead to a linear increase in the flow of liquid out of pipes 33, 34, 35 and 36.

Claims

1. A flow control device for adjusting the rate of flow of a pressurised liquid, the device comprising:

2. A flow control device as claimed in claim 1 , wherein the body is substantially tubular with at least one closed end.

3. A flow control device as claimed in claim 1 or claim 2, wherein the or each aperture is disposed in a side wall of the elongate body.

4. A flow control device as claimed in any of the preceding claims, wherein two opposed apertures are provided.

5. A flow control device as claimed in any of the preceding claims, wherein the aperture or apertures are 2.5mm in diameter.

6. A flow control device as claimed in any of the preceding claims, wherein the body has a diameter of 5.8mm.

7. A flow control device as claimed in any of the preceding claims, wherein the body is mounted in an outer casing.

8. A flow control device as claimed in any of the preceding claims, wherein one or more flow control device is provided within a dribble bar, the dribble bar having a main inlet and a plurality of nozzles.

9. A flow control device as claimed in claim 8, wherein a single flow control device is provided within the dribble bar and the outlet of the flow control device is communication with the nozzles.

10. A flow control device as claimed in claim 8, wherein a plurality of flow control devices are provided within the dribble bar which receive pressurised l iquid from the main inlet and wherein each flow control device is in communication with a single nozzle.

11. A flow control device as claimed in any of the preceding claims, wherein the sheath is made from silicon rubber.

12. A flow control device as claimed in any of the preceding claims, wherein the sheath is 3mm to 3.2mm thick with an internal diameter of 4.8mm to 5mm.

13. A flow control device as claimed in any of the preceding claims, wherein the liquid is a liquid fertiliser.

14. A flow control device as claimed in any of the preceding claims, wherein a pump supplies liquid to the inlet, the pump being operable to control the pressure of the liquid supplied to the inlet.