IE85512B1 - A method and apparatus for metering liquids - Google Patents

Description

Title A Method and Apparatus for Metering Liquids Field of the Invention The invention relates to a method and apparatus for metering a liquid into and out of a container. The invention relates particularly to conveying milk into and out ofa col lcction tanker, but may apply to other liquid foodstuffs, e.g. liquid yeast.

Background to the Invention In general, when a milk tanker collects milk from a farm, milk is pumped into the collection tanker vessel by a positive displacement pump mounted on the tanker.

Alternatively, the milk may be loaded by a vacuum system which pumps air from the tanker, whereupon a system of valves permits the milk to be sucked from the farm tank into the tanker vessel. The latter type of system is especially efficient in clearing the flexible hose which connects the tanker to the farm tank during collections.

It is well known that the collection of mill: in tankers requires an accurate means of metering the milk in and out of the tanker. A common problem is that air can get entrapped in the milk flow and is detected as milk, thus causing an inaccurate reading to be recorded.

Thus, before the milk can be measured. it must be separated from any air entrained in the flow. This is done by means of a vessel called an air eliminator in which milk is forced through a port at the bottom and air is allowed to escape through a port at the top.

Known methods of metering milk in a vacuum type container are described in GB 8323688 A, GB 2|49l43 A and GB 2152679 A.

GB 2 l52679 A discloses a metering method for metering milk comprising, a pipe through which milk is fed from a farm vat to a tanker mounted collection vessel. A turbine flow meter and valves (V2, V3} downstream and upstream of the meter are arranged in the pipe. Upstream of valve (V3) there is arranged a deaerating vessel with 3 Vcnllng Pipe leading, via a valve (V I) from the top of the deaerating vessel to the top of the tanker mounted collection vessel. Probes detect the presence of air in the milk and, monitored by a control unit, control the operation of the valves (V1 to V3).

The systems described above utilise a vacuum type tanker collection vessel in which the interior of the tanker vessel is under vacuum. The present invention is directed to an atmospheric system in which the collection tanker is open to atmosphere. The “vacuum” tanker vessels are so called because a partial vacuum is created in the tanker vessel and, when the tanker vessel is connected by a hose to a farrn milk container, it is the vacuum which draws the milk from the farm container into the tanker vessel.

Because of the physical forces exerted by the vacuum pump on the vacuum type tanker vessel, the vessel it has to be substantially cylindrical in shape, and usually has a greater wall thickness than an atmospheric vessel.

Recently, in an effort to load milk more quickly, atmospheric systems have been used employing centrifugal type pumps which offer the benefit of a higher pumping rate.

Centrifugal pumps, however, have disadvantages in that they require “priming" with a suitable liquid such as water or milk before they will operate and they are unable to clear the collection hose adequately at the end of each collection, which is a necessity for accurate metering of the milk. These disadvantages are overcome to a degree by the fitting of a second pump which is designed to prime the centrifugal pump and to clear the hose.

Object o[ the Invention It is an object ofthe invention to provide an improved apparatus and method for pumping milk (or other liquid foodstufls) into and out of a collection tanker.

It is also an object of the invention to provide a system which allows the use of a centrifugal pump with its attendant benefits, but also offers the ability to clear the intake hose efiiciently, and to measure the collected milk accurately and efficiently. it is also an object of the invention to provide an improved system which handles the milk more quickly and efficiently than known systems.

Summa ft 1 yen on In accordance with a first aspect, the invention provides apparatus for conveying and metering a liquid (e.g. milk) from a first container (e.g. a farm milk tank) to a collection tanker vessel, the interior of which is substantially at atmospheric pressure, comprising: a liquid inlet pipe connectable at an inlet end by a hose to the first container; : pump in fluid connection with the inlet pipe, and adapted to pump liquid from the inlet pipe into an air eliminator vessel; an air venting means communicating with an upper region of the air eliminator vessel; venting valve on the air venting means; a liquid outlet pipe connected, at one end, to a lower region of the air eliminator vessel, and connectable at the other end to an inlet port of the tanker vessel; a metering means disposed in the pipe to meter the volume of liquid conveyed through the metering means; a plurality of valves for controlling the flow of liquid through the apparatus; a plurality of sensors located in selected positions in the apparatus and capable of determining whether air or liquid is in contact therewith; a control unit which controls the operation of the apparatus in response to signals received from the sensors; characterised in that: the upper region of the air eliminator vessel is in fluid communication with a vacuum pump and also is in fluid communication with a source of compressed air, through an air filter; and valve means are provided whereby the air eliminator vessel may alternately be put in fluid communication with the vacuum pump or compressed air source.

Suitably the pump is a centrifugal pump operated by the vehicle's hydraulic system although it may be powered from other sources either on the vehicle or from the mains electricity at the location of the transaction. The vacuum pump used to prime the centrifugal pump may be a venturii pump and may be powered by compressed air from the braking system of the collection tanker. The source of compressed air used to push milk through the system at certain stages of the method of the invention may also be the braking system of the collection tanker. However in this case the compressed air is passed through the air filter before coming into contact with the milk.

In one embodiment the pump is located upstream of the air eliminator vessel. In another embodiment of the invention. the centrifugal pump may be mounted downstream of the air eliminator vessel. In this case, the venturii pump is used to prime the air eliminator vessel and the centrifugal pump is then fed by gravity. The filtered compressed air is only used to push milk through the centrifugal draw (and meter which is downstream from the pump) when necessary.

In accordance with a further aspect, the invention provides a method for conveying and metering a liquid (e.g. milk) from a first container (eg. a farm milk tank) to a collection tanker vessel using an appmtus as defined above.

The method may include the following steps: a) connecting the liquid inlet pipe to the first container, by connection means; b) opening valve means to put the vacuum pump in fluid communication with the inlet pipe whereby a vacuum is created in the inlet pipe to draw liquid into the pump to prime the pump; c) pumping liquid by means of the pump, from the inlet pipe into the air eliminator vessel and from the lower region of the air eliminator vessel, through the metering means, to the collection tanker vessel; d) sensing when a predetennined volume of air has collected in the air eliminating vessel and opening the air venting valve to permit the accumulated air in the air eliminator vessel to vent to atmosphere; e) sensing the presence of air in the pump and switching off the pump; The steps a) to e) are known. The method of the invention is characterised in that it comprises the step of: Opening the compressed air valve means to put the air eliminator vessel in fluid communication with the source of filtered compressed air, and closing inlet valve means in the inlet pipe, whereby accumulated liquid in the air eliminator vessel is pushed by the compressed air from the lower region of the air eliminator vessel through the metering means to the collection tanker vessel.

Preferably, the method of the invention includes the following additional steps: g) closing the compressed air valve means and inlet valve means in the inlet pipe and opening a vacuum valve means whereby the vacuum pump is put in a fluid communication with the air eliminator vessel to create a vacuum within the air eliminator vessel; and h) opening the inlet valve means whereby the vacuum created in the air eliminator vessel is suddenly applied to the hose to suck residual liquid in the hose into the air eliminator vessel.

Suitably, the method of the invention may include the following additional step: '1) following step h) the vacuum valve means and the inlet valve means in the inlet pipe are both closed, and the compressed air valve means is opened to put the air eliminator vessel in fluid communication with the source of filtered compressed air whereby the residual liquid in the air eliminator vessel is pushed by the compressed air from the lower region of the air eliminator vessel through the metering means to the collection tanker vessel; Optionally steps 0 and g) are repeated as necessary to clear substantially all liquid from the hose.

When, following step i), it is sensed that substantially all of the liquid has been drawn into the air eliminator vessel. the compressed air valve is operated to supply a quantity of filtered compressed air to push the liquid to a pre-dctemtinccl level in the air eliminator vessel whereby by finishing the liquid conveying method at this level on ¢,—,,-,1, collection of liquid, each collection may be accurately measured.

Brief Description of the Drggiggs One embodiment of the invention is hereinafter described with reference to the accompanying drawings wherein: Figure l is a schematic diagram of a first embodiment of apparatus for metering milk in accordance with the invention; Figures 2 to 9 are schematic diagrams similar to Figure I showing (in greyscale) the direction of flow and position of milk during the various stages of the method of the invention; and Figure 10 is a schematic diagram of a second embodiment of apparatus for metering milk in accordance with the invention.

Detailed Descri lion 0 t e win Referring to the embodiment Figure I, this illustrates a pumping and metering apparatus for transferring milk from a farm milk tank to a tanker vessel. and at the same time metering the quantity of milk collected by the tanker. The apparatus, which is mounted either on the tanker or on the tractor used to draw the tanker if the tanker is a trailer, in well known manner, comprises a flexible hose 1 I which is connected at its distal end to a farm milk tank (not shown). The proximal end of the hose I I is connected to a milk inlet port 12, which, in turn, is connected to a four-way valve system It} comprising valves V2, V3, V4 and V5 which are all interconnected. The operation of the four-way valve system is also described in my Patent IE 950846. The valves may be butterfly valves, An outlet port 13 ot‘ the four~way valve system is connected by a pipe 14 to a centrifugal pump 15.

An outlet 18 of the put'np,lS is connected by a pipe 16 to an inlet port 17 of an air eliminator vessel 20.

The air eliminator vessel 20 has an air outlet port 21 at the top of the vessel. and a milk outlet port 22 at the bottom of the vessel.

The air outlet port 2! (which also acts as an air inlet port for compressed air, as discussed below) is connected by a pipe 23 to an air exhaust valve V1. The pipe 23 also communicates with branch pipes 24 and 25.

Pipe 24 communicates, via a valve V6. to a venturii pump 30. The venturii pump is powered by compressed air supplied from the tanltcr vehicle's compressed air system, c.g. the brake system. This compressed air, for this purpose, need not be filtered because it is not permitted to come into contact with the milk. It is vented to atmosphere from the venturii pump 30 after me. The branch pipe 25 is connected via valve V7 to a series of air filters 31 which make the air sufficiently clean to come into contact with food products in manufacture. The air filter 31 is, in turn, connected by a pipe to the compressed air system of the tanker vehicle.

At the bottom of the air eliminator vessel 20, the milk outlet port 22 is connected by a pipe 26 to a suitable liquid volume measuring means, for example to a meter 40 for metering the volume of milk passing through the meter 40. The meter 40 is preferably a “rnagflow" (magnetic induction) type meter. Altematively, it may be a turbine flow meter, or a positive displacement type meter, for example.

An outlet of the meter 40 is connected by a pipe 27. which passes through a non-return valve V8 and also through valve V4, to an inlet port I9 of the milk tanker.

The apparatus includes probes Pl, P2, P3, P4 and PS which control the operation of the valves V2, V3, V4 and V5. The probes Pl-PS and the valves V2-VS are all controlled and monitored by a system controller, which may be a microprocessor such as a PLC (programmable logic controller) in well known manner.

Probe Pl is located in the milk inlet pipe 14, eg. in, or adjacent, the centrifugal pump ‘ Probe Pl measures conductivity to indicate the presence of milk or air in the pipe . The probes P2, P4 and P5 are positioned in the air eliminator vessel 20, and probe P3 is located upstream of the milk meter 40. These probes also monitor conductivity to detemiine the presence of either air or milk at the location of the probe and thus. by logic, determine the status of the system.

The apparatus of the invention is suitable for collecting milk from a farm rank into lhc milk tanker vessel; metering the volume of milk collected. It can also be used for dispensing milk from the milk tank vessel into another vessel or tanker. or to a milk processing plant, and metering the volume of milk dispensed. The same milk hose 1 l can be used for both collecting and dispensing.

O ration of t The operation of the apparatus in collecting milk from a farm tank and conveying the milk through the meter 40. and into the tanker collection vessel is now described with reference to Figure I when viewed in conjunction with Figures 2 to 9, which show, in greyscale, the location of the milk in the apparatus, at different stages of the method of the invention. The direction of movement of the milk is shown by arrows.

Priming The milk hose I1 is first connected to the farm tank. Priming of the centrifugal pump now takes place, as is illustrated in Fig. 2. The valves V2 and V6 are opened and valves V3, V4 and VS remain closed. The venturii pump 30 is switched on to create a vacuum in the milk hose ll. This draws milk into the centrifugal pump 15 to prime the pump.

The priming may, in fact, be carried out using any suitable liquid e.g. water.

Priming is necessary because centrifugal pump: cannot pump air, and cease operation when substantial volumes of air are drawn through them.

Pumping V4 is opened and the centrifugal pump 15 then commences operation and milk is pumped by the pump l5 from the farm tank, through pipe 16, into the air eliminator vessel 20, and from there through pipe 26, meter 40, valve V8, pipe 27, and into the tanker inlet port 19, as illustrated in Fig. 3.

Venting During the pumping step, air (from the farm tank or fiorn any leaking unions in the pipework. or indeed any other source) will become entrained in the milk, and is separated from the milk in the air eliminator vessel 20. This is illustrated in Fig. 4. The separation of air from milk in the air eliminator vessel is accomplished in well known manner. The milk separates downwardly in the vessel 20. and the air collects at the top of the vessel. The pressure of the air gathering at the top of the air eliminator vessel pushes the milk level down. When the milk drops below the level of sensor P2, venting of the air commences, as illustrated in Fig. 4. This is achieved by opening air exhaust valve VI [valves V6 and V7 are closed). This pennits the accumulated air in the air eliminator vessel 20 to vent to atmosphere under the pressure of the milk being continually pumped into the vessel 20. The milk will then rise in the vessel 20 to the level shown in Fig. 3.

The venting of air from the system is repeated as necessary during the pumping operation.

Pushing Towards the end of the milk collection. the centrifugal pump I5 begins to draw air from the farm tank, and thus ceases to pump, as shown in Fig. 6. The system controller, in response to probe Pl which senses air in the centrifugal pump l5. then operates to switch~off the pump 15 and close valve V2. Valve V7 is then opened and clean filtered air from filter 3| is pumped through pipes 25, 23 under pressure into the air eliminator vessel 20. The pressurised air pushes milk in the air eliminator vessel 20 through the IO outlet port 22 and meter 40 to the tanker inlet port 19. This creates space in the air eliminator vessel 20 for more milk to be received into the vessel. The air used to pressurise the air eliminator vessel 20 is cleaned and filtered by a filter 31 to a standard suitable for use in food manufacturing. Typically the air is filtered to a 0.0] micron and then passed through an active carbon filter to remove any odours.

The air is taken from the compressed air system (e.g. the brake system) of the tanker vehicle, as described above. This air pressure is typically in the region of 100 to 150 psi, but is reduced in pressure before entering the system. The filtered air pressure is limited to about 0.5 Bar (about 7 psi). This rather low pressure is sufficient to push the milk out of the air eliminator vessel 20, but is not sufficiently high to require the vessel to be a pressure vessel resistant to high pressures.

Clearing Clearing of the residual milk in the milk hose ll, inlet pipe I4, pump I5 and pipe l6, now takes place, and is illustrated in Fig. 7. The controller then operates to close valves V7 and V2 and to open valve V6, and then operates the venturii pump 30 (Fig. 1).

Because V2 is closed, there is now a closed system and the mnning of the venturii pump creates a powerful vacuum in the vessel 20. The vacuum level is allowed to build up in the air eliminator vessel to a a level of between about [2 to 20 inches mg, for example approximately 15 inches/I-lg. Then the valve V2 is opened and the sudden application of this powerful vacuum causes the remaining milk to be sucked, in an efficient manner. to and through the centrifiagal pump l5 (which may be operated briefly to assist the process). and into the air eliminator vessel 20. It has been found that the sudden application of a strong vacuum causes the residual milk in the pipework to be jerked, in a wave-like manner. into the air eliminator vessel 20. thus clearing the piping elliciently of residual milk. If an insuflieient vacuum is applied air only would be sucked into the vessel 20, and the milk would be left in the pipework. The centrifugal pump 15 restarts if the probes sense sufficient milk in the milk inlet pipes.

Finishing The control system then operates to stop the venturii pump. and to close valves V6 and V2. Valve V7 is then opened and pressurised filtered air is again pumped into the air eliminator, as described above, to force the accumulated milk in the air eliminator vessel into the tanker inlet port 19, as previously described above.

The steps of clearing and finishing are repeated as necessary until substantially all milk is conveyed from the farm tank and the connecting pipes.

End of Collectign When the probes indicate that the majority of the milk has been drawn into the air eliminator vessel 20. the system supplies the filtered air to push the liquid to a pre- determined level in the vessel. By finishing at this same level on every milk collection, each collection can be measured accurately. A quantity of milk is lefi in the vessel 20, and pipes 26 and 27 , at all times to ensure that the meter 40 is always flooded. This quantity is known as the “prime". If the total system (including the meter 40) is dry, (typically for the first collection after the system has been washed), this known prime volume is added to the collection (in a well known manner) as it can be seen that this milk will not have passed through the meter, since it now remains upstream of the meter 40.

Account must be taken of this in metering. If it is desired to clear the system completely of milk during collections, the ‘‘prime‘’ may be pushed on, beyond the non- rctum valve V8, by opening valve V7 to allow filtered compressed air into the system to push the milk beyond the non-return valve V8 and into the tanker vessel.

Thus the system can be run as a “dry" system, where the air eliminator 20 and meter 40 is emptied between each collection.

As explained above. the embodiment of the invention as described in relation to Figure I may also be used to dispense milk from the tanker collection vessel and to meter the I2 milk dispensed using the fol-IPW3)’ V3lV° $)'S1¢m V2. V3. V4 and V5. The system Operates as described above, except that valves V2 and V4 are closed and Valves V5 and V3 are opened such that milk from the tanker vessel is routed through the pump 15 and 3" °llmi"3l0f Vessel 20. meter 40, through valve V3 and out through the hose 1 l.

A second, simpler, embodiment of the invention. which is used in a situation where it is desired to collect milk only, but not to dispense and meter milk from the tanker collection vessel, is shown in Figure I0.

In this embodiment the four-way valve system V2, V3, V4 and V5 is omitted from the apparatus. Consequently, the outlet port 13 of the four-way valve system may also be omitted.

With this modified apparatus the method for conveying the milk from a farm milk tank to a collection vessel is substantially the same as that described above with reference to Figures 1 to 9.

Thus, in this simpler embodiment of Figure l0, the flow of milk is from the farm tank, through flexible hose ll, through milk inlet port l2 to pipe 14 and so flows into the eentri fugal pump I5. As with the previous embodiment, an outlet 18 of the pump 15 is connected by a pipe l6 to an inlet port !7 of the air eliminator vessel 20 to deliver the milk into the air eliminator vessel 20. Valve V2 may be mounted either upstream or downstream of the centrifugal pump 15.

The flow of milk from the air eliminator 20 again is substantially the same as that described with reference to the embodiment of Figure 1, except that valve V4 is not utilised, and because of the exclusion of the four-way valve system, the pipeworlt is simpler. Thus. the milk passes through the milk outlet port 22, through the meter 40, through the one-way valve V8, through pipe 27 to the inlet port I9 of the milk tanker.

As indicated above the system can be run. at the end of collection, as a so—callcd “dry" system. This is used where it is important to clear the pipework between collections, for example when the tanker has to travel a long distance between farms, particularly in hot climates where it is desirable to pass all residual milk in mg gysicm into an insulated and cooled tanker.

In the first embodiment of Figure I, this is achieved during the “end of collection" step by opening valve ‘/7 to perrrtit the filtered compressed air into the pipe system to clear all residual milk front the air eliminator vessel 20 and from pipes 26 and 27 through as far as valve V4, where the system includes a four-way valve system.

Where, as in the embodiment of Figure 10 the four-way valve system is omitted, the filtered compressed air pushes the residual milk from the air eliminator vessel 20 through pipe 26 to valve V8.

In both embodiments valve V8 opens, because it is a non~retum valve which allows the milk to pass in one direction only (from left to right in Figs, I and 10). Thus, in the embodiment of Fig. 10 the residual milk flows directly to port 19 and into the tanker. In the embodiment of Fig. 1 the valve V4 is opened to permit the residual milk to flow to port I9 and into the tanker.

The words "comprises/comprising" and the words “havingIincluding" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features. integers. steps, components or groups thereof.

From the foregoing, it will be apparent that numerous modifications and variations can be efiected without departing from the true spirit and scope of the novel concept of the present invention. It will be appreciated that the present disclosure is intended to set forth the cxempliftcations of the invention which are not intended to limit the invention the specific embodiments illustrated. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Where technical features mentioned in any claim are followed by reference signs, these reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims (13)

Claims

1. Apparatus for conveying and metering a liquid (e.g. milk) from a first container (e.g. a farm milk tank) to a collection tanker vessel, the interior of which is substantially at atmospheric pressure, comprising: a liquid inlet pipe (l4, l6) connectable at an inlet end by a hose (I I) to the first container; a pump (1 5) in fluid connection with the inlet pipe (14), and adapted to pump liquid from the inlet pipe (14) into the air eliminator vessel (20); an air venting means (23) communicating with an upper region of an air eliminator vessel (20); a venting valve (V l) on the air venting means (23); a liquid outlet pipe (26, 27) connected, at one end, to a lower region of the air eliminator vessel (20), and oonnectable at the other end to an inlet port (19) of the tanker vessel; a metering means (40) disposed in the pipe (26, 27) to meter the volume of liquid conveyed through the metering means (40); a plurality of valves (V2, V8) for controlling the flow of liquid through the apparatus; a plurality of sensors {Pl-P5) located in selected positions in the apparatus and capable of detemiining whether air or liquid is in contact therewith; a control unit which controls the operation of the apparatus in response to signals received from the sensors; characterised in that: the upper region of the air eliminator vessel (20) is in fluid communication with a vacuum pump (30) and also is in fluid communication with a source of compressed air, through an air filter (31); and valve means (V6, V7) are provided whereby the air eliminator vessel (20) may alternately be put in fluid communication with the vacuum pump (30) or the compressed air source.

2. Apparatus as claimed in claim 1, wherein the pump ( I S) is a centrifugal pump operated by the tanker vehicle's hydraulic system.

3. Apparatus as claimed in claim 1 or claim 2, wherein the vacuum pump used to prime the centrifugal pump is a venturii pump and is powered by compressed air from the braking system of the collection tanker vehicle.

4. Apparatus as claimed in any one of the preceding claims, wherein the source of compressed air used to push millt through the system at certain stages of the method of the invention may also be the braking system of the collection tanker vehicle.

5. Apparatus as claimed in any one of the preceding claims, wherein the pump ( I S) is located upstream of the air eliminator vessel (20).

6. Apparatus as claimed in any of claims I to 4, wherein the centrifugal pump may be mounted downstream of the air eliminator vessel.

7. Apparatus as claimed in any one of the preceding claims, wherein the apparatus may include a four-way valve system (V2. V3, V4 and V5) in fluid connection between a liquid inlet pipe ( l I, I4) and liquid outlet pipe (27), whereby the apparatus may be used to dispense liquid from the tanker collection vessel and to meter the liquid so dispensed.

8. A method for conveying and metering a liquid (e.g. milk) from a first container (eg. a farm milk tank) to a collection tanker vessel using an apparatus as claimed in any one of claims l to 7 comprising: a} connecting the liquid inlet pipe (I4) to the first container. by connection means (I I); b) opening valve means (V2, V6) to put the vacuum pump (30) in fluid communication with the inlet pipe (I4) whereby a vacuum is created in the inlet pipe (14) to draw liquid into the pump (15) to prime the pump (I 5); c) pumping liquid by means of the pump (I 5), from the inlet pipe (I4) into the air eliminator vessel (20) and from the lower region of the air eliminator vessel (20), through the metering means (40), to the collection tanker vessel; sensing when a predetermined volume of air has collected in the air eliminating vessel (20) and opening the air venting valve (V l) to penn it the accumulated air in the air eliminator vessel (20) to vent to atmosphere; sensing the presence of air in the pump (IS) and switching off the pump; characterised in that the method includes the additional step of: opening the compressed air valve means (V7) to put the air eliminator vessel (20) in fluid communication with a source of filtered compressed air and closing valve means (V2) in the liquid inlet pipe (14) whereby accumulated liquid in the air eliminator vessel (20) is pushed by the compressed air from the lower region of the air eliminator vessel (20) through the metering means (40) to the collection tanker vessel.

9. A method as claimed in claim 8, characterised in that it includes the following additional steps: closing the compressed air valve means (V7) and inlet valve means (V2) in the inlet pipe (I 4) and opening a vacuum valve means (V6) whereby the vacuum pump (30) is put in a fluid communication with the air eliminator vessel (20) to create a vacuum within the air eliminator vessel (20); and opening the inlet valve means (V2) whereby the vacuum created in the air eliminator vessel (20) is suddenly applied to the connection means. eg. a hose (1 l), to suck residual liquid in the connection means (I i) into the air eliminator vessel.

10. A method as claimed in claim 9, characterised in that: i) following step h) the vacuum valve means (V6) and the valve means (V2) in the liquid inlet pipe (14) are closed, and the compressed air valve means (V7) is opened to put the air eliminator vessel (20) in fluid communication with the source of filtered compressed air whereby the residual liquid in the air eliminator vessel (20) is pushed by the compressed air from the lower region of the air eliminator vessel (20) through the metering means (40) to the collection tanker vessel.

l l. A method as claimed in claim 9 or claim 10 wherein steps 0 and g) are repeated as necessary to clear substantially all liquid from the connection means which, optionally is a hose [1 I).

I2. A method as claimed in claim 10 or claim ll, wherein when, following step i). it is sensed that substantially all of the liquid has been drawn into the air eliminator vessel (20). the compressed air valve (V7) is operated to supply a quantity of filtered compressed air to push the liquid to a pre-determined level in the air eliminator vessel (20) whereby by finishing the liquid conveying method at this level on each collection of liquid, each collection may accurately be measured. 13. A method as claimed in claim 10 or 11 wherein ifat the end ofthe milk collection system it is desired to operate the milk collection system as a “dry" system in which all residual liquid is cleared from the air eliminator vessel (20) and the pipework between each liquid collection, then following step i) the compressed air valve (V7) is opened to supply a quantity of filtered compressed air to push all residual liquid from the air eliminator vessel (20) and from the liquid outlet pipe(s) (26, 27) and into the tanker vessel. 14. An apparatus, for conveying and metering a liquid (e.g. milk) from a first container to a collection tanker vessel substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

13. A method for conveying and metering a liquid (e.g. milk) from a first container to a collection tanker vessel substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.