GB2369191A - Liquid material batch metering apparatus - Google Patents

Abstract

A pressurisable measuring weigh vessel 21, suspended from a load sensor 12, receives pumped liquid or fluent material to be weighed in batches through a combined inlet/outlet pipe 22 from a supply pipe 24 and an inlet valve. The weighed liquid is delivered through the pipe 22 and an outlet valve to a delivery pipe 25 under the pressure of compressed air from a pipe 19. The weighing is conducted in a closed vessel, avoiding disadvantages associated with the liquid being open to the atmosphere, and the system requires fewer valves compared with prior art apparatus.

Description

Metering apparatus This invention is concerned with metering apparatus, and relates in particular to the metering by weight of batches of liquid.

There are numerous occasions where it is required to measure out a specified weight of some liquid material. One such is found in the treatment of batches of seed, or some other particulate substance, to apply to it a fungicide or to provide it with a protective or growth-enhancing coating (such a process, and equipment for effecting the process, is the subject of our co-pending British Patent Application No: 25/9/99; Publication No :,, ; P1574). A batch of the particles is placed in a coating chamber, and a precise amount of liquid is metered into the chamber for application to the surface of the particles.

One problem to be dealt with is how accurately and consistently to measure out the liquid to be employed.

The presently standard method uses a measuring weigh vessel, open at the top, suspended from a load sensor.

Liquid is fed into the vessel from above, with no physical connection between the supply pipe and the measuring vessel that might cause a load on the vEsseL.

Accordingly, the load sensor's output gives a true indication of the weight of the vessel plus the liquid, and-by subtraction of the empty vessel's weight, the liquid itself. The discharge of the liquid from the vessel is by gravity via a valved outlet at the bottom of the vessel. The liquid is allowed simply to drop out into a second open-topped vessel, and again there is no physical connection with the receiving vessel.

No pressure can be generated at this point, so where the liquid must be moved further, a third element must be involved. Typically this is a pressurisable transfer vessel, having a valve inlet above and a valved outlet below it, and after closing the liquid inlet valve the vessel is simply pressurised to blow the contents out when the outlet valve at the bottom is opened.

In operation the weigh vessel is filled conventionally-through the outlet valve of the main liquid storage container-to the set point. The vessel's outlet valve and the transfer vessel's inlet valve are then opened to allow the liquid to run under gravity into the transfer vessel. When the sensed weight is zero, those two valves are closed, and a supply of compressed air is then applied to the top of the transfer vessel, and the vessel's outlet valve is opened to drive the liquid through a delivery pipe to the delivery point.

This is relatively complicated, and requires a minimum of four valves capable of handling the liquid at sufficient flow under gravity. Furthermore, the passage of the liquid material through the open air between the vessels is a significant disadvantage in the case where the liquid is one that is hazardous to health, flammable, quick drying, and/or volatile, or that has an unpleasant odour. Moreover, in order to ensure that all of the liquid is delivered from the transfer vessel, thus maintaining the accuracy of the dose, the compressed air supply has to be kept on for an adequate period. This inevitably leaves the delivery pipe substantially empty of liquid after each delivery, and yet a film of liquid can remain that dries out, leaving a deposit that thickens, batch after batch, and so causes progressive blockage.

Other problems are associated with this standard technique. Thus, in practice it is sometimes necessary to deliver batches fairly rapidly, so that it becomes necessary to fill the weigh vessel simultaneously with the discharge of the previous batch from the transfer vessel. A further disadvantage then arises where a change is to be made either to the dose, or to the actual liquid being metered. In this case, the change must be made one batch in advance of the delivery. For example, if the batches of liquid are required to coat a solid particulate material (such as seed) being fed in batches from a supply source, then when the supply source is almost exhausted, it is sometimes necessary to handle a smaller than normal batch. This condition may not be apparent until the particulate batching apparatus fails to fill a complete batch. At this point the liquid weigh vessel has already filled the next batch of liquid-sufficient for a normal batch of particles whereas a reduced batch of liquid is requiredcorrespondingly to the reduced batch of particles.

Likewise a different batch of particles might require a different liquid additive. For example, a different seed type may require a different fungicide.

Again, the change must be anticipated one batch in advance of the particle change.

The present invention proposes a novel form of batch metering apparatus that substantially reduces, or even does away with, such problems. The invention suggests the use not of an open weigh vessel but of a closed one, which closed vessel can therefore also be the transfer vessel. More particularly, the invention suggests using a substantially-closed, pressurisable measuring vessel suspendable from a load sensor and having a generally horizontally-orientated flexible combined inlet/outlet pipe at the in-use lower part of the vessel, which pipe is connectable, at a pipe junction at a fixed (i. e. not supported from the load sensor) point, both to an input pipe (via an input supply valve) and also to an output pipe (via an output delivery valve). The input pipe runs between a source of the liquid to be metered and the supply valve, via a pressurising pump, and the output pipe runs between the delivery valve and the delivery point for the metered liquid. The vessel also has a generally horizontallyorientated flexible air inlet pipe at the in-use upper part of the vessel by which pipe the vessel is connectable to a source of compressed air via a suitable regulator (conveniently a relieving-type air pressure regulator-i. e. one that can reduce the downstream air pressure if it rises above the set pressure, as well as increase it if it falls below).

In one aspect, therefore, the invention provides a liquid material batch metering system comprising: a pressurisable closed combined weigh-and transfer vessel suspended from a load sensor, the vessel having a generally horizontally orientated flexible combined inlet/outlet pipe at the in-use lower part of the vessel, which pipe is connected, at a pipe junction at a fixed point, both to an input pipe (via an input supply valve) and also to an output pipe (via an output delivery valve), which input and output pipes are connectable respectively to a source of and a delivery point for the metered material, the vessel also having a generally horizontally orientated flexible air inlet pipe at the in-use upper part of the vessel by which pipe the vessel is connectable to a source of compressed air via a suitable regulator.

The invention provides a liquid material batch metering system-that is, a system for metering out a liquid in batches. The liquid can be of any sort, as required, and can even be a flowable"solid"-a fine powder, for example-but is likely to be an actual liquid.

The size of the batches can be whatever is required for the job at hand and the vessels available-thus, from as little as a few pounds/kilograms up to as much as a ton (around 1, 000 kg).

The metering system of the invention includes a pressurisable closed combined weigh-and-transfer vessel.

This vessel may take any convenient form, and be made of any appropriate material and to any suitable size, and no more need be said about it at this time.

The vessel used in the invention's metering system is suspended from a load sensor. This can conveniently be effected using any of the sensors and suspension means used or suggested for use in the Art, and no more need be said about it here.

The vessel has a generally horizontally-orientated flexible combined inlet/outlet pipe at the in-use lower part of the vessel, and a generally horizontallyorientated flexible air inlet pipe at the in-use upper part of the vessel. The object of the two pipes being generally horizontal is to reduce and control the effect their weight and their internal pressure have on the load sensor. It is known that a flexible pipe connecting a vessel suspended from a load sensor is likely to exert a force on the vessel that will be transmitted to the sensor, thus interfering with the accuracy of weight measurement. Furthermore, pressure in the pipe is likely to influence the force applied.

(In Bordon tube pressure gauges, this principle is exploited to actually measure the pressure). In the invention this force is made to be substantially constant since the internal pressure in both connecting pipes is held substantially constant. The air pressure, and hence the effect of the top pipe, can be accurately constant. The pressure in the lower pipe is the sum of the air pressure and the liquid height in the vessel.

The latter varies but is a small component of the total.

However, there is also a change in the dynamic pressure in the lower pipe (there must be a pressure gradient in any pipe in order for flow to take place). Therefore the lower pipe will experience an increased pressure at the fixed end, falling to zero at the vessel end during filling, and a corresponding decreased pressure at the fixed end falling to zero at the vessel end during discharge. These pressure variations can be made small by choosing a relatively large diameter pipe. In any case, the filling pressure difference does not affect accuracy at all since the high weight reading is taken under static conditions after the fill process is complete. The discharge pressure difference is small and is constant from dose to dose. It can therefore be automatically compensated in the control software. This is discussed further hereinafter.

Incidentally, the term"generally horizontallyorientated"covers quite a wide range of angles the pipe might actually have to the horizon. Without being limited by this, though, there is here meant from around zero to around twenty degrees-and the smaller the better.

The various pipes used in the system of the invention can, like the vessel, be of any convenient size, shape and material, and no more need be said about that here.

The vessel used in the system of the invention has a combined inlet/outlet pipe at the in-use lower part of the vessel, which pipe is connected at a junction at a fixed point-that is, one which is fixedly supported independently of the load sensor-both to an input pipe (via an input supply valve) and also to an output pipe (via an output delivery valve). The junction may be regarded as a simple Y-or T-junction, and the valves can, like the rest of the apparatus, take any suitable form, and no more need be said about this here.

However, it is desirable that the pipes from the junction to and from the valves be arranged generally vertical (which, with appropriate alterations, may be construed in a manner similar to"generally horizontal"), and it is especially preferred that the pipes inputting material to the vessel be below the combined inlet/outlet pipe while those outputting material from the vessel be above that pipe.

The input and output pipes leading to/from the junction are connectable respectively to a source of and a delivery point for the metered material (in the line to the source itself there will usually be a pump, to drive the liquid from the source along through the inlet valve and on into the vessel, while-as discussed below - in the line to the delivery point there will usually be a variable valve). The air inlet pipe at the in-use upper part of the vessel is connectable to a source of compressed air via a suitable regulator (and specifically a relieving-type air pressure regulatori. e. one that can reduce the downstream air pressure if it rises above the set pressure, as well as increase it if it falls below). These pipes can take any appropriate form etc, and no more need be said about them at this time.

Because the output from most load sensors under changing load conditions is more accurate when the change is small, and occurs at a low rate, it is convenient to include, in the output pipe to the delivery point, a variable valve-typically a constriction valve of some sort-so that the the output flow rate can be adjusted during actual delivery.

Initially the valve will be fully open, but as the batch nears its final value the valve will be partially closed to reduce the flow rate and so improve the system's accuracy.

After being connected up to both a source of and a delivery point for the material to be batch metered, and to a compressed air source, the liquid material batch metering system of the invention is operated as follows.

First, the air pressure regulator is set such that when the weigh vessel is partially filled with the liquid, and the delivery valve is opened, the air pressure will be able to drive the liquid out through the delivery valve and pipe to the delivery point at a rate suitable for the process. This pressure is maintained constant throughout the metering process.

The liquid pump on the supply side must be capable of pumping liquid into the weigh vessel, via the supply valve, against the air pressure in the weigh vessel, at a rate suitable for the process.

Then, to meter the liquid, the supply valve is opened, and liquid is pumped into the vessel. The flow is terminated by closing the supply valve when an arbitrary gross weight is reached-that weight must include a quantity of liquid in excess of the required dose. The required dose is then deducted from this figure to give a low weight set point. When delivery of the measured dose is required, the delivery valve is opened to allow the pressure inside the vessel to drive the liquid to the delivery point, until the low set point is reached, at which time the delivery valve is closed to stop the flow.

The actual controlling device is conveniently a microprocessor (or some similar form of computer), and conventional software therein can be used to measure the actual weight at the termination of input and of output, the difference being the actual achieved dose. Any error can then be used to modify the calculation of the low set point for the next dose, thus avoiding repetition of the error.

As noted above, the flexible pipes are likely to exert a force that will interfering with the accuracy of weight measurement, as will pressure in the pipes. In the invention, though, this force is made to be substantially constant since the internal pressure in both connecting pipes is held substantially constantthe air pressure and hence the top pipe can be accurately constant, while the pressure in the lower pipe, the sum of the air pressure and the liquid height, varies but is only a small component of the total.

There is also a change in the dynamic pressure in the pipe; the lower pipe will experience an increased pressure at the fixed end, falling to zero at the vessel end during filling, and a corresponding decreased pressure at the fixed end falling to zero at the vessel end during discharge. These pressure variations can be made small by choosing a relatively large diameter pipe.

In any case, the filling pressure difference does not affect accuracy at all since the high weight reading is taken under static conditions after the fill process is complete. The discharge pressure difference is small and is constant from dose to dose. It can therefore be automatically compensated in the control software.

If a change is required in the liquid being metered, the following procedure can be instigated.

First, the air supply to the weigh vessel is shut off.

The liquid pressurising pump is then reversed, and the supply valve is opened. After a delay to allow the pressure in the weigh vessel to decay, the delivery valve is opened, and the pump then draws all liquid in the system-in the weigh vessel and the complete pipe system-back to the original supply container. The two liquid valves are then closed, and the air pressure is restored to the weigh vessel. Finally, the new liquid is introduced into the weigh vessel, and one or more batches are delivered (diverted to a catchment vessel if necessary) in order to fill the delivery pipe.

It can also be advantageous to use a plurality of weigh vessels so as to be able to respond instantly to a required change of liquid. Where only one of a set of possible liquids is required, a number of weigh vessels can be suspended from a single load sensor. This arrangement can also be used where liquids-are to be dispensed consecutively, but not simultaneously.

Simultaneous dispensing would require a separate device for each liquid.

Where multiple weigh chambers are suspended from a single load sensor, then the dead weight of the total suspended assembly may be large compared to the metered dose, which may reduce accuracy. To mitigate this problem a it is possible to exert a constant upward force on the assembly that reduces the dead weight carried by the load sensor. This can be achieved employing a balance arm and counterweight system, for example-a horizontal arm with a weight at one end and, at the other end, a linear force transmitting device that exerts an upward force to the suspended assembly without applying any turning moment to it.

Advantages of the invention over the known and presently-utilised Art are:1. The system is less complicated with fewer elements.

2. There is no contact between the liquid being handled and free air (there is contact with the air inside the weigh vessel but this does not communicate with the atmosphere generally), thus avoiding contact of process workers with a hazardous product, flammable risk, unpleasant odour, or the drying out of product (the air inside the weigh vessel will become saturated with vapour from the liquid after which no further evaporation can take place.).

3. Since flow is not generated by gravity alone, the rates of flow can be greater, or pipes and valves can be smaller.

4. The delivery pipe is maintained full of liquid, thus avoiding the problem of drying out and depositing solid materials that can progressively block the pipe.

5. Where batches of liquid are required to match other elements of a batch process, such as in the application of fungicides to seed, the conventional open-vessel system of the Art must operate in one of two modes.

In slow mode it responds to a demand for a batch, by going through the weighing and transfer to transfer vessel before it can deliver the batch.

In fast mode it weighs a second batch during transfer of the previous one and then immediately transfers the second batch to the transfer vessel.

In that case it cannot respond immediately to a required change in the dose.

The device according to the invention, on the other hand, can simultaneously offer both an immediate response to a demand for delivery of a batch of liquid (equivalent to fast mode in the Art), and can also change the required dose at any time up to commencement of delivery, or even after commencement (equivalent to slow mode in the Art.) 6. Where a change in the liquid to be metered is required (for example a change in seed type may provoke a change in fungicide type) the Art, if operating in fast mode, cannot respond to the change immediately. The final batch will already be in the transfer vessel and must be used or diverted to a catchment vessel. With the invention, the liquid in the vessel can be removed and the new one charged, as described above.

7. Multiple weigh vessels are possible, arranged vertically so that the transmitted force from any of them exerts a purely downward force on the load sensor. This allows for rapid changing of liquids or for sequential applications of different liquids without recourse to full duplication of the whole dispenser.

An embodiment of the invention is now described, though by way of illustration only, with reference to the accompanying diagrammatic Drawings in which: Figure 1 shows an example of the Prior Art liquid material batch metering system; Figure 2 shows an example of the liquid material batch metering system of the invention; and Figure 3 shows another example of the liquid material batch metering system of the invention, using multiple weigh vessels.

Figure 1 shows an example of the Prior Art liquid material batch metering system.

The system uses a measuring weigh vessel (11), open at the top, suspended from a load sensor (12). Liquid is fed into the vessel 11 from above, with no physical connection between the valved supply pipe (13) and the measuring vessel 11 that might cause a load on the vessel. Accordingly, the output of the load sensor 12 output gives a true indication of the weight of the vessel plus the liquid, and-by subtraction of the empty vessel's weight, of the liquid itself.

The discharge of the liquid from the vessel 11 is by gravity via a valved outlet (14) at the bottom of the vessel. The liquid is allowed simply to drop out into a second open-topped vessel (15), and again there is no physical connection with the receiving vessel 15.

No pressure can be generated at this point, so where the liquid must be moved further, a third element must be involved. Typically this is a pressurisable transfer vessel (16), having a valved inlet (17) above and a valved outlet (18) below it, and after closing the liquid inlet valve 17 the vessel is simply pressurised to blow the contents out when the outlet valve 18 at the bottom is opened.

In operation the weigh vessel 11 is filled conventionally-through the outlet valve of the main liquid storage container (not shown) -to the set point.

The vessel's outlet valve 14 and the transfer vessel's input valve 17 are both then opened to allow the liquid to run under gravity into the second open-topped vessel 15 and thence into the transfer vessel 16 (the latter's outlet valve 18 is of course closed). When the sensed weight is zero, those two valves are closed, and a supply of compressed air A is then applied along input pipe (19) to the top of the transfer vessel 16, and the vessel's outlet valve 18 is opened to drive the liquid through a delivery pipe to the delivery point (not shown).

Figure 2 shows an example of the liquid material batch metering system of the invention.

The system comprises a pressurisable closed combined weigh-and-transfer vessel (21) suspended from load sensor 12. The vessel 21 has a generally horizontally-orientated flexible combined inlet/outlet pipe (22) at the in-use lower (as viewed) part of the vessel, which pipe 22 is connected, at a pipe junction (23) at a fixed point (not shown), both to an input pipe (24, via an input supply valve) and also to an output pipe (25, via an output delivery valve), which input and output pipes 24,25 are connectable respectively to a source of and a delivery point for (neither shown) the metered material. In the path to the delivery point there is also a flow restriction/control valve (26).

The vessel 21 also has a generally horizontallyorientated flexible air inlet pipe 19 at the in-use upper part of the vessel by which pipe the vessel is connectable to a source of compressed air A via a suitable regulator (not shown).

The operation of the invention's system is as follows. First, the apparatus is connected up to both a source of and a delivery point for the material to be batch metered, and to a compressed air source. Next, the air pressure regulator (not shown) is set such that when the weigh vessel 21 is partially filled with the liquid, and the delivery valve 25 is opened, the air pressure will be able to drive the liquid out through the delivery valve and pipe 2S to the delivery point at a rate suitable for the process. All valves are then closed.

Then, to meter the liquid, the supply valve 24 is opened, and liquid is pumped (by a pump not shown) into the vessel 21. The flow is terminated by closing the supply valve 24 when there is reached some arbitrary gross weight that includes a quantity of liquid in excess of the required dose. The required dose is then deducted from this figure to give a low weight set point. When delivery of the measured dose is required, the delivery valve 25 is opened to allow the pressure inside the vessel to drive the liquid through the flow rate-controlling restriction valve 26 to the delivery point, until the low set point is reached, at which time the delivery valve is closed to stop the flow. The overall output flow rate can be varied as required using the restrictor/control valve 26.

Figure 3 shows another example of the liquid material batch metering system of the invention, using multiple weigh vessels.

Three weigh chambers 21 linked by a rigid arm (31) are suspended from a single load sensor 12. This means that the dead weight of the total suspended assembly may be large compared to the metered dose, which may significantly reduce accuracy. To mitigate this problem a"balance"device (generally 32) is provided to exert a constant upward force on the assembly that reduces the dead weight carried by the load sensor. This device is comprised of a pivoted horizontal arm (33) with a weight (34) at one end and, at the other end, a linear force transmitting device (35) that exerts an upward force to the suspended assembly without applying any turning moment on it.

Claims (12)

1. Claims 1. A liquid material batch metering system comprising: a pressurisable closed combined weigh-and transfer vessel suspended from a load sensor, the vessel having a generally horizontally orientated flexible combined inlet/outlet pipe at the in-use lower part of the vessel, which pipe is connected, at a pipe junction at a fixed point, both to an input pipe (via an input supply valve) and also to an output pipe (via an output delivery valve), which input and output pipes are connectable respectively to a source of and a delivery point for the metered material, the vessel also having a generally horizontally orientated flexible air inlet pipe at the in-use upper part of the vessel by which pipe the vessel is connectable to a source of compressed air via a suitable regulator.
2. 2. A metering system as claimed in Claim 1, wherein the combined inlet/outlet pipe is a relatively large diameter pipe
3. 3. A metering system as claimed in either of the preceding Claims, wherein the pipes from the junction to and from the valves are arranged generally vertical.
4. 4. A metering system as claimed in Claim 3, wherein the pipes inputting material to the vessel be below the combined inlet/outlet pipe while those outputting material from the vessel be above that pipe.
5. 5. A metering system as claimed in any of the preceding Claims, wherein there is included, in the output pipe to the delivery point, a variable valve so that the the output flow rate can be adjusted during actual delivery.
6. 6. A metering system as claimed in any of the preceding Claims, wherein there is means to control the operation of the several valves.
7. 7. A metering system as claimed in Claim 6, wherein the control means is a microprocessor, and software running thereon is used to measure the actual weight at the termination of input and of output, the difference being the actual achieved dose.
8. 8. A metering system as claimed in Claim 7, wherein changes in the dynamic pressure in the pipes are automatically compensated for in the control software.
9. 9. A metering system as claimed in any of the preceding Claims, wherein there is a plurality of weigh vessels so as to be able to respond instantly to a required change of liquid.
10. 10. A metering system as claimed in Claim 9, wherein, where only one of a set of possible liquids is required, the weigh vessels are suspended from a single load sensor.
11. 11. A metering system as claimed in Claim 10, wherein, because the dead weight of the total suspended assembly may be large compared to the metered dose, there is exert a constant upward force on the assembly that reduces the dead weight carried by the load sensor, and this is achieved employing a balance arm and counterweight system including a linear force transmitting device that exerts an upward force to the suspended assembly without applying any turning moment to it.
12. 12. A metering system as claimed in any of the preceding Claims and substantially as described hereinbefore.