GB1593283A - Liquid diluters - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO LIQUID DILUTERS (71) We, J.H. GOOCH & COMPANY LIMITED, a British Company, of Henfield Road, Albourne, Hassocks, Sussex, BN6 9DD, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to diluters for introducing a liquid additive, such as a liquid concentrate, into a main flow of liquid, as one example the addition of a liquid fertilizer in measured proportion to a flow of water for use in horticulture or agriculture.

The application of fertilizer by spreading a dry material on the soil is well known but has many disadvantages. It is not usually possible to apply the fertilizer evenly so that there is a tendency to use additional material with results that the cost is increased.

The labour required to spread the ferilizer is a further item of cost. It is therefore now known to apply fertilizer as a dilute aqueous solution. By the use of a liquid fertilizer concentrate, this can be dispensed through a distribution network in a main flow of water using diluters which are already known in a number of forms.

In one known type of diluter (US patents Nos. 2 618 510 and 3 556 141 for example) the water flows through a main conduit in which there is some kind of restriction, e.g.

a sharp-edge orifice or a venturi, and a reservoir of the liquid concentrate is subjected to the water pressure upstream of the restriction. Opening into the water conduit downstream of the restriction is a smaller bore outlet pipe from the reservoir so that the upstream water pressure thus forces concentrate through the pipe into the main water flow downstream of the restriction.

Typically, a control or metering valve, such as a needle valve, is provided in the outlet pipe from the reservoir to vary the flow of the concentrate and thus adjust the dilution ratio in the main feed water flow.

These diluters suffer from a disadvantage which arises from the common user requirement for a wide range of flow rates, with a maximum throughput often six or seven times the minimum throughput. Such a throughput range implies a pressure drop range of 36 to 49 (square law relation) and the passages for the two different liquids will exhibit a change in flow characteristics at different flow rates which occur at different throughput rates of the diluter: e.g. one of the liquid flows will change from streamline flow to turbulent flow at a different operating point than that of the other liquid flow.

For this reason diluters of this general type have a reputation for being inaccurate.

Another known form of diluter passes concentrate through a first small tube and the water through a number of further tubes of similar size, the dilution ratio being set by the number of water tubes. As the tubes are long in relation to their diameter, typically the length is over 100 diameters, the flow through them is turbulent and not streamline. Although the pressure drop is intended to be the same in each of the tubes it is very sensitive to the condition of the inside walls of the tubes. In use the concentrate tube becomes fouled on its inner wall with undissolved particles, which alters the flow through it, and so this diluter also has a reputation for being inaccurate.

To overcome these disadvantages there are more complex diluters known which incorporate a device for measuring the flow of water and for automatically controlling electrically operated dispensing equipment which injects the correct proportions of fertilizer into the metered water flow, the fertilizer being drawn from an open tank or drum. Such equipment is of course very expensive. Moreover, the control mechanisms are necessarily complex and this means that they are more subject to malfunction and their repair requires the services of a specialist.

According to the present invention, there is provided a diluter comprising respective first and second spaces for a main flow of liquid from an inlet connection and for a liquid additive to be admixed with the main flow, and outlets from said spaces leading to.

a common exit opening for the mixed flow of the liquids, means for controlling the pressure in the liquid additive space in accordance with the pressure in said space for the main flow, said outlets from the first and second spaces leading to the common exit opening being in the form of orifices (by "orifice" is meant for example a hole through a partition wall), at least the main liquid first space having a plurality of said orifices opening from it and the orifices for both said first and second spaces being each of the same size and shape.

Preferably, said orifices are designed as plate orifices - that is to say having a diameter, or an equivalent diameter of the cross-sectional area where this is not circular, at least equal to the axial length of the aperture. In this way it is possible to maintain non-turbulent flow conditions down to very low flow rates so that there is a substantially direct relationship between the rate of flow and the square root of the pressure head across the apertures. It is, however, possible to have orifices of other forms, e.g. as convergent or divergent nozzles.

In an advantageous form of the invention, means are provided for selectively closing one or more of said orifices for adjustment of the dilution ratio of the liquid additive. In this way the adjustment can be made without in any way affecting the similar flow patterns of the two different liquids through their orifices.

In a preferred arrangement, said second space communicates with a further space having a displaceable boundary wall, conveniently formed by a flexible diaphragm or bag, on which the pressure of the liquid in said first space is arranged to act. The liquid additive in the flexible bag can thereby be expelled, with equal pressure force, by way of said second space through said at least one aperture for admixture with the main liquid flow. In one form, the further space can be disposed in the same container as said first and second spaces, where a nonsealing baffle member may be provided as a dividing wall between said first space and the region containing the further space.

Alternatively, said further space may be provided in its own container having connecting conduits to said first and second spaces which are formed in a further container provided with said series of outlet apertures, in which case the two containers may be disposed in positions remote from each other.

It is possible to arrange that a dispenser according to the invention is manually replenished with the liquid additive. Alternatively, however, there may be means for the automatic replenishment of the additive liquid so that the diluter can function for long periods without attention, and advantageously said replenishment means comprises a differential pressure switch with respective pressure-sensing connections to said first and second spaces. It can conveniently be provided, moreover, that the movement of said displaceable boundary wall is arranged to cause a change of pressure in said second space for actuation of said switch upon the loss of liquid from said further space, thereby initiating said replenishment at the required stage.

In one such arrangement, pumping means are arranged to be automatically actuated for pumping a supply of liquid additive to said second space. In another arrangement, the replenishment may be provided by a gravity feed through a non-return valve and pressure-release means are provided for actuation by said switch to relieve the supply pressure in the first space and permit a replenishment flow through said non-return valve.

Embodiments of the invention will now be more particularly described by way of exmaple with reference to the accompanying drawings, wherein: Figure 1 is a sectional elevation of a first diluter according to the invention, Figure 2 is a detail view of one outlet aperture or orifice in the diluter of Figure 1, Figure 3 illustrates a modification of the filler tube cap of the diluter in Figure 1 to adapt the diluter for automatic replenishment, Figure 4 illustrates in plan the diluter of Figure 1 with the cap of Figure 3 and the means for automatic replenishment of the liquid additive, Figures 5 and 6 illustrate two further diluters according to the invention with means for automatic replenishment of the liquid additive, and Figure 7 illustrates a pressure-sensitive switch such as may be employed in the embodiments of Figures 4 to 6.

In the example of Figure 1 of the drawings, the diluter comprises a main casing 2 that has a base 4 and top plate 6 and upper and lower cylindrical walls 8, 10 separated by an orifice plate 12, these casing parts being held together by tension bolts (not shown) extending between holes 14 in the base and top plates. A vertical filler tube 16 extends through aperture 18 in the orifice plate and engages the bore sealingly. The tube also extends through and is sealingly secured to a baffle plate 20 below the orifice plate. Both the plates 12, 20 may for example have a screw-threaded connection with the tube 16. The baffle plate comprises a cylindrical collar 24 that seals against the underside of the orifice plate 12, but the outer rim of the baffle plate is spaced from the adjacent cylindrical wall 10 of the casing.

The closed lower end of the filler tube 16 projects into a flexible plastics bag 28 which has a sealing strip 30 around its neck holding it against the outer wall of the tube. Within the extent of the tube inside the bag there are a number of apertures 32 and there are further apertures 34 in the tube in the extent between the orifice and baffle plates.

The main casing has a water inlet 36 below the baffle plate and a mixture outlet 38 above the baffle plate. The filler tube has a screw closure cap 40 on its upper end projecting from the casing, the cap clamping a sealing ring 42 against the casing top plate 6. Communication between the upper and lower sides of the baffle plate is established by means of a first series of small orifices or nozzles 44 in the annular region of the plate radially outwards of the collar 24, and a second series of small orifices or nozzles 46 radially inwards of the collar. All the orifices 44, 46 are of identical shape and size.

lt will be seen that, as described so far, the water inlet 36 opens into a first inlet space 50 formed in the main casing below the orifice plate, but this is sealed from a further inlet space 52, formed between the baffle and orifice plates and encircled by the collar 24, for a concentrated additive that can be introduced through the filler tube 16.

The first inlet space 50 communicates directly with the region 54 beneath the baffle plate so that the pressure in the region 54 is controlled in accordance with the water inlet pressure, and in said region there is a separate chamber or further space 56, sealed off by the flexible plastics bag 28. The space 56 provides a reservoir of the liquid concentrate and the bag 28 forms a flexible diaphragm boundary on which the inlet water pressure acts, so as to supply concentrate to the space 52. The first and second inlet spaces 50, 52 are both connected by their respective series of orifices 44, 46 to outlet space 58 above the orifice plates and so to the mixture outlet 38.

Thus, in use, liqid concentrate is put into the bag through the filler tube, and when the water inlet 36 is connected to a water supply conduit 36a (Figure 4) the inlet pressure acts on the bag, since there is free communication from the water inlet, around the outer rim of the baffle plate, to the region 54 below the plate. The water pressure produces a flow of water through the first series of orifices 44 and also forces the concentrate into the second space 52 and from there through the second series of orifices 46, so that both water and concentrate mingle in the outlet mixture space 58 and a diluted flow enters outlet conduit 38a (Figure 4). It will be noted that both series of orifices will have the same pressure on their inlet side, since this is determined by the water inlet pressure. Similarly since they open into the same outlet space the flow through each nozzle will be subject to the same pressure drop, and there will be corresponding rates of flow through the individual orifices.

It has already been mentioned that the shape and size of the orifices of both series are the same. The liquid fertilizer concentrates normally used are materials such as aqueous solutions of chemical salts and they will have substantially the same viscosity as water and have only a marginally high density, the effects of which on the rate of flow through the nozzles can be calculated and compensated for. The flow conditions at every one of the nozzles are nevertheless substantially identical, and as a result, it can be expected that variation of the water flow rate will produce a strictly proportional variation in the flow rate of the liquid concentrate. In other words, the dilution ratio of the concentrate will be determined by the relative numbers of orifices opening from the respective inlet spaces 50, 52 into the outlet space 58 and will be the same over a wide variation of flow rates.

Preferably, to ensure that this proportional effect is obtained over as wide a range as possible, in particular extending into very low rates, the orifices are constructed as plate orifices, i.e. having an axial length not greater than their diameter (or the equivalent diameter of their cross-sectional area if they are not circular) although it is possible to employ other orifice or nozzle forms. On the other hand, it may be desirable to have a relatively thick orifice plate, particularly if a plastics material is to be used for economical manufacture of the plate. Both features can be obtained using the construction illustrated in Figure 2, where the relatively thick orifice plate has such plate orifices 60 occupying only a small part of the thickness or depth of the plate and there is a considerably larger diameter counterbore 62 leading to the orifice. The figure also shows the use of a filter layer 64 applied to the underside of the orifice plate which can prevent the blocking of individual orifices by foreign matter, which would alter the dilution ratio of the concentrate.

Preferably there is a large number of orifices in each series, although of course a larger number of orifices will be required for the water flow. As an example the numbers may be in the ratio of 100:1 - e.g. 198 orifices in the first series and 2 orifices in the second series. By providing considerable numbers of orifices it is possible to preset finely graduated adjustments of the dilution ratio by blocking individual orifices and so changing the ratio of operative orifices in the two series. If desired this can be very simply done by removing the orifice plate from the casing, peeling off the filter layer from its underside, applying adhesive tape to said underside of the plate to cover the orifices that are not required, and sticking the filter layer on again. Alternatively it can be done without dismantling the apparatus, if screw-threaded plungers 66 (only one being shown) are mounted on the top plate to be movable upwards and downwards to uncover and cover individual orifices.

The plastics bag 28 is preferably of an opaque material, e.g. white polyethylene, so that it can be seen through a series of transparent plugs 68 that are inserted at different heights in the cylindrical wall 10.

When the liquid concentrate is poured in, the bag is pressed against the inner face of the cylindrical wall and can be seen through the transparent plugs. As the concentrate is dispensed, the bag begins to collapse and, since the concentrate will have a slightly higher specific gravity than water the upper part of the bag will form a substantially level interface between the concentrate and the water admitted to the lower space. Progressively, therefore, the bage is no longer visible at the upper plugs so that the operator has indication of the quantity of concentrate remaining and will know when replenishment is needed. It may however be preferred for the lower cylindrical wall 10 to be made of a transparent material. To refill the bag it is simply necessary to stop the water flow so as to cut off the casing from the supply pressure, to unscrew the cap 40 from the filler tube, and to pour in the required concentrate.

The diluter illustrated in Figures 1 and 2 can be modified to allow it to be automatically replenished, as is illustrated in Figures 3 and 4. The filler tube cap 40 is replaced by a screw cap 70 into which open an inlet pipe 72 and a fine bore tube 74 providing a pressure tapping. A further pressure tapping connection 76 is taken from the water inlet space 50, a removable plug 78 for this purpose being shown in Figure 1. The inlet pipe 72 extends to an electrically driven pump 80 which is able to pump concentrate from an open reservoir 82 into the inlet pipe and the pump motor 84 is switched on and off by a pressure-sensitive control switch 86 connected to the two pressure tappings 74, 76.

In operation, when the concentrate within the collapsible bag 28 is consumed the pressure in the filler tube 16, which has previously been maintained hydrostatically at the water inlet pressure, falls to the outlet pressure in the outlet space 58. A pressure difference thus appears between the two pressure tappings 74, 76 and the switch 86 is actuated to start the pump motor 84 and refill the collapsible bag 28. Pumping continues until the bag is full when the pressure in the filler tube rises above the inlet water pressure, it being arranged that this change in the pressure difference operates the switch 86 to stop the pump.

Another example of an automatically replenishing apparatus is shown in Figure 5.

This uses no pump, there being a gravity feed of the liquid concentrate from the reservoir 82 into the casing 2 through inlet pipe 72, with a non-return valve 88, to a filler tube cap 70 similar to that shown in Figure 3. The two pressure tappings 74, 76 are connected to the pressure-sensitive switch 86, as before, which now actuates a valve 90 in the water supply conduit 36a.

In normal operation the valve 90 is open and the non-return valve 88 prevents any backflow into the reservoir 82. When with the exhaustion of the concentrate in the collapsible bag 28, the pressure tappings 74, 76 sense a pressure differential in the manner already described, the switch 86 is actuated to close off the water supply valve 90. The reservoir pressure head is arranged to be greater than the pressure in the outlet conduit 38a and thus concentrate flows under gravity through the non-return valve 88 to replenish the collapsible bag. As the bag is refilled, the pressure in the first tapping 74 rises to match the pressure head in the reservoir and the switch is then operated again, as already described, to change over the valve 90 and re-establish flow through the diluter.

Another example of an automatically replenished diluter according to the invention is shown in Figure 6, where parts corresponding to those already described are indicated by the same reference numbers. In this example the concentrated liquid additive is contained in a separate casing 102. The water supply is brought through supply pipe 36a to a pressure vessel 104 in which the orifice plate 12 forms an internal partition and the inlet space 106 is connected by conduit 108 to the interior of the casing 102. The supply pipe 72 from the concentrate reservoir connects with the filler tube 16 through a union conduit 109 that also has an outlet branch pipe 110. The inlet water pressure thus acts on the collapsable bag 28 to force concentrate through the union conduit 109 and the branch pipe 110 to a compartment 112 in the pressure vessel on the inlet side of the orifice plate 12. The space 106 thus corresponds to the first inlet space of the first-described embodiment and the compartment 112 corresponds to the further inlet space, the orifice plate being provided with the two series of similar orifices, as already described, for the passage of the fluids from these two spaces.

Although this embodiment can be arranged to be manually replenished, as illustrated there are pressure tappings 74, 76 sensing the water inlet presure and the pressure of the concentrate in the filler tube 16 connected to the collapsible bag 28 in order to actuate the pressure-sensitive switch 86 for operation of a pump (not shown) to introduce further concentrate into the bag through the inlet pipe 72. It will be clear that the manner of operation of this embodiment is as already described for the embodiment of Figure 4, although the diluter internal spaces are differently arranged, and it can similarly be modified to gravity feed, in the manner exemplified in Figure 5.

It will be understood that the connections between the pressure vessel 104 and the casing 102 can be of considerable length so that these may be some distance apart. It is also possible to have a number of discrete compartments in the pressure vessel, corresponding to the illustrated compartment 112, each with outlet orifices in the plate 16 and each with its own concentrate supply arrangement corresponding to the arrangement shown in Figure 6, so that a number of different additives can be mixed with the main flow each in its own chosen proportion. Moreover, it will be clear that the number of such additives can be changed without affecting the concentration of the others per unit volume of the main flow.

A preferred arrangement of the pressuresensitive switch is shown in Figure 7 for use with the automatically replenishing arrangements described above. This has a balance arm regulating mechanism in which two enclosed vessels 120 122 are suspended by wires 126 from opposite ends of a balance arm 128 pivoted at 130 on a support 132.

Each vessel has an upper outlet 134 and the two upper outlets are connected directly together by a flexible tube 136. Lower unions 138, 140 in the vessels are connected to the respective pressure tappings 74, 76 already described: thus, the connection of 138 may be to the water inlet pressure at 36 and the connection of 140 may be to the concentrate pressure in 16.

The pivoting of the arm of the support is limited by end stops 142 and an electrical gravity switch 144 (e.g. a mercury switch) is fixed upon the arm. This switch has the above-described electrical connections to the pump motor 84 (Figures 3 and 6) or the closure valve 90 (Figure 5). In each of the two vessels there is a float valve 146 on the liquid surface 148 in the vessel. The valve 146 may be in the form of a buoyant rubber or flexible plastics disc.

During the operation of the diluter, the first vessel 120 will fill partly with water and the second vessel 122 partly with concentrate, via their connections 74, 76. Since both liquids are then at the same pressure within the diluter, the liquid levels will establish themselves in substantially the same horizontal plane and there will be trapped air above the liquid in both vessels and in their inter-connecting tube 136.

When the concentrate in the diluter is running out, the pressure in the second vessel 122 drops in the manner already described, so that the water level in the first vessel rises and some of the trapped air is displaced into the second vessel. The first vessel 120 is now heavier than the second vessel 122 and the balance arm 128 tilts onto the left-hand end stop, the switch 144 being thereby operated, to start the pump motor 84 or change over the closure valve 90, as the case may be.

When the plastics bag 28 has been fully replenished the increase of pressure in the filler tube 16 drives liquid into the second vessel 122 so that the liquid level in the first vessel 120 now drops below that in the vessel 122 and the change in relative weight of the two vessels swings the arm 128 in the opposite direction to the illustrated position. The switch 144 is thereby operated to terminate the replenishment of the concentrate container. The arm 128 will remain in this position during the normal operation of the diluter until the need for replenishment is again sensed, so that the switch is always positively held in one or other end position, this effect being obtained by choice of the level of the pivot 130 relative to the line joining the attachment points of the two suspension wires 126 to the arm 128.

The float valves 146 have the function of preventing passage of liquid between the two vessels 120, 122 and also of minimixing the air-liquid surface contact area in each vessel to reduce the absorption of the trapped air into the liquid.

It will be clear that modifications of the illustrated arrangements are possible with the scope of the present invention. For example, when automatic control is provided it is possible to replace electrical control means by hydraulically or pneumatically operated control means, in generally known manner. The replenishment of the concentrate can also be carried out using a continuously running pump with a modulating valve that maintains pressure balance, so that there is no interruption whatsoever in the flow of the diluted mixture. Moreover it is possible to adapt the diluter to dispense a plurality of concentrate feeds in the water supply.

It will be appreciated that although the invention has been particularly described with reference to the use of diluters for distribution of liquid fertilizer concentrate in water, the apparatus can be employed in many other applications in different fields of industry, e.g. in food processing, adding a liquid flavouring or colouring to a main flow of a beverage.

WHAT WE CLAIM IS: 1. A diluter comprising respective first and second spaces for a main flow of liquid from an inlet connection and for a liquid additive to be admixed with the main flow, and outlets from said spaces leading to a common exit opening for the mixed flow of the liquids, means for controlling the pressure in the liquid additive space in accordance with the pressure in said space for the main flow, said outlets from the first and second spaces leading to the common exit opening being in the form of orifices, at least the main liquid first space having a plurality of said orifices opening from it and the orifices for both said first and second spaces being each of the same size and shape.

2. A diluter according to claim 1 wherein each orifice provides a flow passage with a cross-sectional area of diameter or equivalent diameter at least equal to its axial length.

3. A diluter according to claim 2 wherein the orifices are formed in a wall or walls of thickness greater than said equivalent diameter and each said orifice opens into a larger cross-section recess occupying a part of said wall thickness such that the remaining wall thickness at the orifice is not greater than said equivalent diameter.

4. A diluter according to any one of claims 1 to 3 wherein means are provided for selectively closing one or more of said orifices for adjustment of the dilution ratio of the liquid additive.

5. A diluter according to any one of the preceding claims wherein said second space communicates with a further space having a displaceable boundary wall on which the pressure of the liquid in said first space is arranged to act to expel liquid from said further space through the second space and the outlet orifice or orifices thereof for admixture with the main liquid flow.

6. A diluter according to claim 5 wherein the displaceable boundary wall is formed by a flexible diaphragm.

7. A diluter according to claim 6 wherein said further space is formed by a flexible bag.

8. A diluter according to any one of claims 5 to 7 wherein said further space is formed as an internal chamber of a rigid container that is in communication with said first space for transmission of said main liquid pressure to said further space.

9. A diluter according to claim 8 wherein said container has connecting conduits to said first and second spaces which are formed in a further container provided with said series of outlet apertures, whereby the two containers can be disposed at a distance apart.

10. A diluter according to claim 8 or claim 9 wherein said container for the further space comprises at least one wall portion of transparent or translucent material through which said displaceable boundary wall can be viewed for indicating the quantity of liquid additive remaining in said further space.

11. A diluter according to any one of the preceding claims having replenishment means for the supply of liquid additive from a reservoir to said second space, said replenishment means comprising a differentialpressure switch with respective pressuresensing connections to said first and second spaces whereby to actuate replenishment in response to a fall in pressure in said second space relative to the pressure in said first space.

12. A diluter according to any one of claims 5 to 10 together with claim 11 wherein the movement of said displaceable boundary wall is arranged to cause a pressure change with the loss of additive liquid from said further space whereby said switch is actuated.

13. A diluter according to claim 11 or claim 12 comprising an additive liquid reservoir for supplying said second space by gravity feed through a non-return valve, and pr

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. It will be appreciated that although the invention has been particularly described with reference to the use of diluters for distribution of liquid fertilizer concentrate in water, the apparatus can be employed in many other applications in different fields of industry, e.g. in food processing, adding a liquid flavouring or colouring to a main flow of a beverage. WHAT WE CLAIM IS:

1. A diluter comprising respective first and second spaces for a main flow of liquid from an inlet connection and for a liquid additive to be admixed with the main flow, and outlets from said spaces leading to a common exit opening for the mixed flow of the liquids, means for controlling the pressure in the liquid additive space in accordance with the pressure in said space for the main flow, said outlets from the first and second spaces leading to the common exit opening being in the form of orifices, at least the main liquid first space having a plurality of said orifices opening from it and the orifices for both said first and second spaces being each of the same size and shape.

2. A diluter according to claim 1 wherein each orifice provides a flow passage with a cross-sectional area of diameter or equivalent diameter at least equal to its axial length.

3. A diluter according to claim 2 wherein the orifices are formed in a wall or walls of thickness greater than said equivalent diameter and each said orifice opens into a larger cross-section recess occupying a part of said wall thickness such that the remaining wall thickness at the orifice is not greater than said equivalent diameter.

4. A diluter according to any one of claims 1 to 3 wherein means are provided for selectively closing one or more of said orifices for adjustment of the dilution ratio of the liquid additive.

5. A diluter according to any one of the preceding claims wherein said second space communicates with a further space having a displaceable boundary wall on which the pressure of the liquid in said first space is arranged to act to expel liquid from said further space through the second space and the outlet orifice or orifices thereof for admixture with the main liquid flow.

6. A diluter according to claim 5 wherein the displaceable boundary wall is formed by a flexible diaphragm.

7. A diluter according to claim 6 wherein said further space is formed by a flexible bag.

8. A diluter according to any one of claims 5 to 7 wherein said further space is formed as an internal chamber of a rigid container that is in communication with said first space for transmission of said main liquid pressure to said further space.

9. A diluter according to claim 8 wherein said container has connecting conduits to said first and second spaces which are formed in a further container provided with said series of outlet apertures, whereby the two containers can be disposed at a distance apart.

10. A diluter according to claim 8 or claim 9 wherein said container for the further space comprises at least one wall portion of transparent or translucent material through which said displaceable boundary wall can be viewed for indicating the quantity of liquid additive remaining in said further space.

11. A diluter according to any one of the preceding claims having replenishment means for the supply of liquid additive from a reservoir to said second space, said replenishment means comprising a differentialpressure switch with respective pressuresensing connections to said first and second spaces whereby to actuate replenishment in response to a fall in pressure in said second space relative to the pressure in said first space.

12. A diluter according to any one of claims 5 to 10 together with claim 11 wherein the movement of said displaceable boundary wall is arranged to cause a pressure change with the loss of additive liquid from said further space whereby said switch is actuated.

13. A diluter according to claim 11 or claim 12 comprising an additive liquid reservoir for supplying said second space by gravity feed through a non-return valve, and pressure-release means actuable by said differential pressure switch to relieve the main liquid supply pressure in said first space and permit a replenishment flow through said non-return valve.

14. A diluter according to claim 11 or claim 12 comprising pumping means for supplying said second space with replenishment liquid from the reservoir and said differential pressure switch is arranged to actuate the pumping means.

15. A diluter according to any one of claims 11 to 14 wherein said pressuresensitive switch comprises two vessels with respective top outlets that are intercon nected , and each with a bottom outlet connected respectively to the main liquid flow pressure and the liquid additive pressure upstream of the orifices, whereby the relative weights of the two vessels varies with relative variation of the pressures of the two liquids and product displacements dependent thereon.

16. A diluter according to claim 15 wherein the vessels are mounted on a balance arm to pivot the arm with said variation in relative weights.

17. A diluter for the admixture of a

liquid additive with a main flow of liquid, constructed and arranged for use and operation substantially as described herein with reference to any of the examples illustrated in the accompanying drawings.