GB2617399A

GB2617399A - Dosing apparatus and method

Info

Publication number: GB2617399A
Application number: GB2205201.3A
Authority: GB
Inventors: Donaldson Rebecca; Stakes Thomas; Kabla Alexandre
Original assignee: Blue Tap Solutions Ltd
Current assignee: Blue Tap Solutions Ltd
Priority date: 2022-04-08
Filing date: 2022-04-08
Publication date: 2023-10-11
Also published as: GB202205201D0

Abstract

A dosing apparatus 100 for dispensing a first liquid 3a into a flow of a second liquid 3b inside a main conduit 1 comprises a pressure transfer assembly comprising a first 3 and second compartment 2, a first conduit 6 for fluid flow between the main conduit and the second compartment 2, wherein the first compartment and the second compartment are arranged for transfer of pressure from the liquid in the second compartment to exert a corresponding pressure on the liquid in the first compartment, means 5 for drawing the liquid in the first compartment into the flow of the second liquid in the main conduit. There may be pressure release valves and air-release valves 8 present. The first liquid may be refilled from an external reservoir. The means for drawing the liquid from the first compartment may comprise a Venturi or an eductor.

Description

I

DOSING APPARATUS AND METHOD

The present invention relates to dosing apparatus for dispensing a first liquid into a flow of a second liquid, and an associated method. In particular the invention relates to, but is not limited to, apparatus for dispensing a dose of one liquid into a pipe containing another liquid. For example, the invention is applicable, but in no way limited, to dispensing a dose of chlorine (more particularly, a chlorine solution) into a flow of water, to render the water safe to drink.

Background

Dosing apparatuses for dispensing a certain quantity of a first liquid into a flow of a second liquid have many practical applications. For example, dosing apparatus may be provided for dispensing a dose of chlorine into a potentially-contaminated water supply, to achieve a particular concentration of chlorine in the water, in order to output a supply of disinfected water, e.g. which is fit to drink. A further example is the dispensing of a fertiliser into water for the purpose of fertigation.

In many applications, it is important that the dosing system is able to reliably and accurately dispense a specific quantity of a first liquid (e.g. a chlorine solution or fertiliser) into the flow of the second liquid (e.g. water). For example, when adding a chlorine solution to water, it is important the that the concentration of the chlorine in the water output from the dosing system falls within an acceptable range. Adding either too much or too little chlorine into the water could be dangerous for a consumer of the water. In other words, it is important that the correct amount of chlorine is added per unit of water.

In some applications, the flow rate of the second liquid may be variable. For example, for dosing apparatus that is configured to add a chlorine solution to a flow of water in a pipe from a water supply, the pressure and flow rate of the water in the pipe may vary depending on several different factors, such as the water pressure of the upstream water supply, and the current level of demand downstream of the dosing apparatus. Some such dosing systems are arranged to add a first liquid into the flow of the second liquid at a constant rate. As a result, when the flow rate of the second liquid changes, the concentration of the first liquid in the second liquid also changes.

However, this is undesirable in many applications where precise dosing is required. To mitigate against this problem, some dosing systems employ a 'proportional dosing' arrangement that aims to maintain a constant dose (concentration) of the first liquid in the second liquid, independently of variations in the flow rate of the second liquid.

A first type of proportional dosing system uses an electrical controller to control the addition of the first liquid to the second liquid. However, such systems are unsuitable for environments with no supply of electricity (or an unreliable or intermittent supply of electricity). A second type of proportional dosing system utilises a complex mechanical arrangement of pistons and valves to control the addition of the first liquid to the second liquid. However, these types of system have a high mechanical complexity, and the large number of parts decreases the reliability of the system, increases the difficultly of maintenance, and increases the cost of production. A third type of proportional dosing system comprises a venturi-based controller, wherein a 'Venturi' device pulls the first liquid into the second liquid. However, in a venturibased system, whilst the dose of the first liquid is independent of the flow rate of the second liquid through the system, it is not independent of the pressure of the second liquid. Therefore, when variations in the pressure of the second liquid occur, the apparatus is unable to deliver the first liquid at a constant dose into the second liquid.

More generally, there is a need for improved dosing apparatus for accurately and reliably dispensing a dose of a first liquid into a flow of a second liquid.

Summary

The present invention seeks to provide apparatus and methods for addressing or at least partially ameliorating one or more of the above issues.

In a first aspect the invention provides dosing apparatus for dispensing a first liquid into a flow of a second liquid inside a main conduit, the dosing apparatus comprising: a pressure transfer assembly comprising a first compartment configured for containing a reservoir of the first liquid, and a second compartment configured for containing a reservoir of the second liquid; a first conduit for fluid flow, wherein the first conduit is coupled to the second compartment for fluid flow of the second fluid between the main conduit and the second compartment, wherein the first compartment and the second compartment are arranged for transfer of pressure from the second liquid inside the second compartment to exert a corresponding pressure on the first liquid in the first compartment; means for drawing the first liquid from the first compartment and into the flow of the second liquid inside the main conduit as the second liquid flows along the main conduit, the drawing being driven by the flow of the second fluid along the main conduit; and a second conduit for fluid flow, for fluid flow from the first compartment to the means for drawing the first liquid from the first compartment; wherein the second conduit comprises a one-way valve configured for preventing flow of fluid from the main conduit into the first compartment; wherein the dosing apparatus comprises a pressure release valve that is coupled to the second compartment for releasing second liquid from the second compartment when the pressure of the second liquid inside the second compartment exceeds a threshold level; wherein the dosing apparatus comprises a first air-release valve that is coupled to the first compartment for releasing air from the first compartment; and wherein the dosing apparatus comprises a second air-release valve that is coupled to the second compartment for releasing air from the second compartment.

By virtue of the one-way valve, the dosing apparatus is advantageously able to prevent flow of the second liquid into the first compartment, which would dilute the reservoir of the second liquid in the first compartment and decrease the accuracy of the dosing.

By virtue of the pressure release valve, the dosing apparatus is advantageously able to release second liquid from the second compartment when the dosing apparatus is subject to abnormal conditions (e.g. abnormally high pressure of the second liquid in the main conduit), preventing an excessive build-up of pressure in the second compartment from occurring.

By virtue of the first and second air-release valves, air from the first and second compartments can be removed. Advantageously, this increases the accuracy of the dose of the first liquid dispensed by the dosing apparatus.

The dosing apparatus may comprise a refill valve that is coupled to the first compartment and is configurable to allow a flow of the first liquid into the first compartment By virtue of the provision of the refill valve, the first compartment can be re-filled rather than being replaced. Advantageously, this reduces the operating cost of the dosing apparatus and reduces waste that would otherwise be created through the use of a single-use compartment. Moreover, the risk of leakage caused by installation of a replacement first compartment is avoided.

The refill valve may be operable by a user to manually fill the first compartment with the first liquid.

By virtue of the refill valve being operable by a user to manually fill the first compartment, the need for electrically powered refill apparatus (e.g. comprising an electrical pump, valve or actuator) is avoided. For example, when the dosing apparatus is for dispensing a chlorine solution into a flow of water to provide safe drinking water, the dosing apparatus can be deployed to under-resourced areas which do not have a reliable supply of electricity (or no supply of electricity at all).

The means for drawing the first liquid from the first compartment may comprise an eductor.

The means for drawing the first liquid from the first compartment may comprise a Venturi.

The first liquid may comprise chlorine (more particularly, a chlorine solution) and the second liquid may comprise water.

The first liquid may comprise a fertiliser and the second liquid may comprise water.

At least one of the first air-release valve and the second air-release valve may be provided on an upper surface of the pressure transfer assembly.

By virtue of the provision of the first air-release valve and the second air-release valve on the upper surface of the pressure transfer assembly, a more compact dosing apparatus can be provided. Moreover, when the first air-release valve and the second air-release valve are provided on the upper surface, the air can be more reliably extracted from the first and second compartments.

The dosing apparatus may comprise a dosing valve for selectively allowing flow of the first liquid along the second conduit to mix with the second liquid in the main conduit.

The dosing apparatus may comprise a valve for selectively allowing flow of the second liquid along the first conduit.

The dosing apparatus may comprise a valve for selectively allowing pressure to be transferred from the liquid inside the main conduit to the liquid inside the second compartment.

By virtue of the dosing valve, the valve for selectively allowing flow of the second liquid along the first conduit, and the valve for selectively allowing pressure to be transferred from the liquid inside the main conduit to the liquid inside the second compartment, the dosing apparatus can be more easily installed (e.g. coupled to a main conduit), the reservoir of liquid inside the first compartment can be more easily managed (e.g. refilled), and leaks or other failures in the dosing apparatus can be more easily isolated.

The dosing apparatus may comprise a configurable valve that is configurable between: a first configuration for allowing a flow of the first liquid into the first compartment from an external reservoir, and for preventing a flow of the first liquid from the first compartment and into the flow of the second liquid inside the main conduit; and a second configuration for allowing a flow of the first liquid from the first compartment and into the flow of the second liquid inside the main conduit, and for preventing a flow of the first liquid into the first compartment from the external reservoir.

By virtue of the configurable valve, the risk of a user error in the operation of the dosing apparatus is beneficially reduced. In other words, the risk of a user opening the refill valve to fill the first compartment with the first liquid whilst liquid is still able to flow from the first compartment and into the main conduit (which would result in an inaccurate or unpredictable amount of the first liquid flowing into the main conduit) is avoided.

At least one of a length or diameter of the second conduit may be configured for dispensing a predetermined amount of the first liquid into the second liquid inside the main conduit, per unit volume of second liquid that flows along the main conduit.

The second conduit may be configured to induce a predetermined pressure loss between the first compartment and the main conduit, for dispensing a predetermined amount of the first liquid into the second liquid inside the main conduit, per unit volume of second liquid that flows along the main conduit.

The second conduit may comprise at least one of an orifice plate, valve (e.g. needle valve or butterfly valve), expansion or contraction for inducing the predetermined pressure loss between the first compartment and the main conduit.

Advantageously, therefore, the configuration of the second conduit provides a mechanically simple and reliable means or adjusting or controlling the dose of the first liquid that flows into the main conduit.

The first compartment may comprise a deformable bag.

The first compartment may comprise a deformable bellows.

The first compartment may comprise a deformable balloon.

The first compartment may be disposed inside the second compartment.

Alternatively, the pressure transfer assembly may for example comprise a deformable diaphragm between the first compartment and the second compartment, for transfer of pressure from the second liquid inside the second compartment to the first liquid inside the first compartment. Accordingly, the first compartment may be adjacent to the second compartment.

The first compartment may be divided into a plurality of sub-compartments, wherein each sub-compartment is configured for containing a respective reservoir of the first liquid, and wherein each sub-compartment is coupled to the second conduit for flow of the first liquid into the second conduit. Advantageously, this allows for greater flexibility when using fabrication methods which are limited in respect of size, as a plurality of smaller sub-compartments can be used where it is impossible to fabricate one large compartment.

By virtue of the provision of the deformable bag, deformable diaphragm, deformable bellows, deformable balloon, or the plurality of sub-compartments, pressure from the second liquid inside the second compartment is efficiently transferred to the first liquid inside the first compartment. Advantageously, this results in more accurate dosing of the first liquid into the main conduit.

Each of the sub-compartments may comprise a deformable bellows, deformable balloon or deformable bag.

Preferably the dosing apparatus does not require the use of electricity in order to dispense the first liquid into the flow of the second liquid inside the main conduit. Likewise, preferably the dosing apparatus does not require electricity in order to fill the second compartment with the first liquid via the refill valve. Advantageously, this enables the dosing apparatus to be deployed in environments in which no supply of electricity is available (or only an unreliable or intermittent supply of electricity is available). Moreover, the complexity of the dosing apparatus is reduced, since there is no need to ensure isolation (for safety reasons) between a supply of electricity and the liquids that are flowing through the system.

The main conduit may comprise a tube or pipe.

At least one of the first conduit or the second conduit may comprise a tube or pipe, or any other type of fluidic coupling, and need not necessarily be elongate.

The means for drawing the first liquid from the first compartment and into the flow of the second liquid inside the main conduit preferably comprises threaded connections.

The use of threaded connections advantageously reduces leakage and allows the pressure reduction geometry to be easily inserted and removed from an existing pipeline.

In a second aspect the invention provides dosing apparatus for dispensing a first liquid into a flow of a second liquid inside a main conduit, the dosing apparatus comprising: a pressure transfer assembly comprising a first compartment configured for containing a reservoir of the first liquid, and a second compartment configured for containing a reservoir of the second liquid; a first conduit for fluid flow, wherein the first conduit is coupled to the second compartment for fluid flow of the second fluid between the main conduit and the second compartment, wherein the first compartment and the second compartment are arranged for transfer of pressure from the second liquid inside the second compartment to exert a corresponding pressure on the first liquid in the first compartment; means for drawing the first liquid from the first compartment and into the flow of the second liquid inside the main conduit as the second liquid flows along the main conduit, the drawing being driven by the flow of the second fluid along the main conduit; and a second conduit for fluid flow, for fluid flow from the first compartment to the means for drawing the first liquid from the first compartment The second conduit may comprise a one-way valve configured for preventing flow of liquid from the main conduit into the first compartment.

The dosing apparatus may comprise at least one of: a pressure release valve that is coupled to the second compartment for releasing second liquid from the second compartment when the pressure of the second liquid inside the second compartment exceeds a threshold level; a first air-release valve that is coupled to the first compartment for releasing air from the first compartment; and/or a second air-release valve that is coupled to the second compartment for releasing air from the second compartment.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently (or in combination with) any other disclosed and/or illustrated features. In particular but without limitation the features of any of the claims dependent from a particular independent claim may be introduced into that independent claim in any combination or individually.

Any of the features set out above for the first aspect may also be used in the second aspect.

In a third aspect the invention provides a method of dispensing a first liquid into a flow of a second liquid inside a main conduit using the dosing apparatus according to the first aspect or the second aspect.

Brief description of the drawings

Embodiments of the invention will now be described by way of example only with reference to the attached figures in which: Figure 1 shows a schematic cross-sectional overview of a dosing apparatus having a pressure transfer assembly which, in this case, comprises a deformable bag, Figure 2 shows a modified version of the dosing apparatus of Figure 1; Figure 3 shows a modified version of the dosing apparatus of Figure 2, in which a one-way valve is additionally provided; Figure 4 shows a dosing apparatus in which the pressure transfer assembly comprises a deformable diaphragm; the pressure transfer assembly Figure 5 shows a dosing apparatus in which comprises an expandable bellows; the pressure transfer assembly Figure 6 shows a dosing apparatus in which comprises an expandable balloon; and Figure 7 shows a dosing apparatus in which the pressure transfer assembly is divided into multiple compartments, comprising a compartment for the second liquid, and a plurality of compartments for the first liquid.

Detailed description

The present embodiments represent the best ways known to the Applicant of putting the invention into practice. However, they are not the only ways in which this can be achieved.

Overview Figure 1 shows, for illustrative purposes, dosing apparatus 100 for dispensing a first liquid 3a (which may otherwise be referred to as an 'injection fluid' herein) into a flow of a second liquid 3b (which may otherwise be referred to as a 'motive fluid' herein), as the second liquid (motive fluid) 3b flows through a main conduit 1, in a flow direction indicated by arrow F. The injection fluid 3a may be a chemical used for the treatment of the motive fluid 3b. For example, the injection fluid 3a may comprise a chlorine solution or a fertiliser. More generally, the dosing apparatus 100 is for dispensing the first liquid 3a into a flow of the second liquid 3b inside the main conduit 1.

The dosing apparatus uses an entirely hydraulic system to ensure the dosing ratio (the ratio of the flow rates of the injection fluid 3a and the motive fluid 3b) is independent of the inlet pressure. The injection fluid 3a is pumped into the motive fluid 3h using the pressure difference generated by the flow of the motive fluid through a pressure reduction geometry 5. As described later, the pressure reduction geometry 5 may comprise an eductor or a so-called 'Venturi'. The high pressure at the inlet of the pressure reduction geometry 5 is used to pressurise the injection fluid 3a by means of a pressure transfer assembly provided within a pressure vessel 2.

The motive fluid (second liquid) 3b can flow between the main conduit 1 and the pressure vessel 2 via a first conduit 6. The injection fluid (first liquid) 3a is separated from the pressurised fluid 3b inside the pressure vessel 2 using a deformable (e.g. flexible) injection reservoir 3 which is, for example, in the form of a deformable bag.

This injection reservoir 3 allows pressure to be transferred between the two liquids without the liquids mixing. The pressure difference between the high pressure in the pressure vessel 2 and the lower pressure generated by the flow of the motive fluid 3b is used to drive the flow of the injection fluid 3a (via a second conduit 10) into the motive fluid 3h in the main conduit 1.

In other words, the dosing apparatus 100 comprises a vessel having a first compartment 3 and a second compartment 2, the first compartment 3 being configured for containing a reservoir of the first liquid 3a. The dosing apparatus 100 comprises means 5 for drawing the first liquid from the first compartment 3 and into the flow of the second liquid 3b inside the main conduit 1 as the second liquid 3b flows along the main conduit 1. A first conduit 6 is coupled to the second compartment 2 for fluid flow between the main conduit 1 and the second compartment 2, for transfer of pressure from the second liquid 3b inside the main conduit 1 to exert a corresponding pressure on the first compartment 3 (and therefore on the first liquid 3a inside the first compartment 3).

The main conduit 1 may also be referred to as a 'pipeline', 'tube' or 'pipe' in the present disclosure, although it will be appreciated that any suitable conduit for fluid flow may be used.

Pressure reduction geometry This pressure reduction geometry 5 inside the main conduit 1 is used to reduce the pressure of the motive fluid (second liquid) 3b as it flows through the pressure reduction geometry 5. This pressure drop is a function of the flow rate of the motive fluid 3b in the pipeline. The difference in pressure created by the pressure reduction geometry 5 is used to drive flow around the dosing apparatus 100. This pressure reduction geometry 5 is preferably made from a material that is safe for use with drinking-water and is compatible for contact with the injected fluid (first liquid) 3a. The roughness of the inside wall of the pressure reduction geometry 5 is preferably minimised, to reduce the non-recoverable pressure drop in the motive fluid 3b, and therefore the energy required to drive flow through the apparatus 100.

Advantageously, the pressure reduction geometry 5 does not require a supply of electricity in order to operate.

In a particularly advantageous configuration, the pressure reduction geometry 5 is manufactured with threaded connections, using a thread size and standard that is ubiquitous in the chosen deployment area. The use of threaded connections advantageously reduces leakage and allows the pressure reduction geometry to be easily inserted and removed from an existing pipeline.

The pressure reduction geometry 5 contains an injection port 5a. This port 5a is the means through which the injection tubing 10 (also referred to as the 'second conduit' 10) is hydraulically connected to the pressure reduction geometry 5. This connection is airtight and provides a path through which the injection fluid 3a flows from the injection tubing 10 to the point of minimum pressure (or low-pressure point') in the pressure reduction geometry 5.

At least one of a length or diameter of the second conduit 10 may be configured for dispensing a predetermined amount of the first liquid 3a into the second liquid 3b inside the main conduit 1, per unit volume of second liquid that flows along the main conduit.

The second conduit 10 may be configured to induce a predetermined pressure loss between the first compartment 3 and the main conduit 1, for dispensing a predetermined amount of the first liquid 3a into the second liquid 3b inside the main conduit 1, per unit volume of second liquid 3b that flows along the main conduit 1.

For example, the second conduit 10 may comprise at least one of an orifice plate, valve (e.g. needle valve or butterfly valve), expansion, or contraction for inducing the predetermined pressure loss between the first compartment 3 and the main conduit 1.

Examples of pressure reduction geometry that could be used in the dosing apparatus 100 include, but are not limited to, a Venturi tube' and an 'orifice plate'.

A Venturi tube (also referred to as simply a 'Venturi') is a pipe section which comprises a gradual contraction which reduces the pipe diameter, a short length of straight pipe at this reduced diameter, and a gradual diffuser which expands the pipe back to its original diameter. A flow of fluid through this geometry exhibits the Venturi Effect, whereby the fluid velocity increases and the pressure decreases as the diameter of the pipe decreases. The point in the pipe where the diameter is the smallest is known as the 'Vena Contracta'. This is the region in which the pressure is lowest and the velocity is highest. When a Venturi tube geometry is used, the Vena Contracta is preferably used as the injection point.

An orifice plate is a flat plate with a hole in its centre that placed in the cross section of a pipe (e.g. in the main conduit 1). The hole in the centre of the plate has the effect of instantaneously (or near instantaneously) reducing the diameter of the pipe to the diameter of the hole. As fluid flows through the smaller diameter of the orifice plate, the velocity increases and the pressure reduces. In typical water systems the flow rate through an orifice plate will be high enough such that flow downstream of the orifice plate separates from the walls of the pipe as it flows through it. This leaves a small region of low-pressure fluid (sometimes referred to as a Vacuum') circulating a small distance downstream of the orifice plate. When an orifice plate geometry is used as the pressure reduction geometry 5, this region of low-pressure fluid is preferable used as the injection point.

More generally, the dosing apparatus 100 comprises means for drawing the first liquid 3a from the first compartment 3 and into the flow of the second liquid 3b inside the main conduit 1 as the second liquid 3b flows along the main conduit 1, the drawing being driven by the flow of the second fluid along the main conduit. The means for drawing the first liquid from the first compartment may comprise an eductor. The means for drawing the first liquid from the first compartment may comprise the above-described Venturi or orifice plate.

Pressurisation port The pressurization port 6a is a connection upstream of the pressure reduction geometry 5, where the pipe diameter (diameter or width of the main conduit 1) is large. This port 6a provides an external hydraulic connection, upstream of the high-pressure inlet of the pressure reduction geometry 5. The pressurization port 6a is connected to the pressure vessel 2 via a pressurization line 6 (also referred to as a first conduit 6). The port 6a is preferably made from plastic and contains a threaded connection.

Pressurisation line The pressurization line 6 provides a hydraulic connection between the pressurization port 6a and the pressure vessel 2.

In operation, initially a small portion of the second liquid 3b in the main pipeline 1 flows through the pressurization line 6 into the pressure vessel 2, until the pressure vessel 2 is completely filled (the vessel 2 will already be partially filled due to the first liquid 3a in the injection reservoir 3). Once the vessel 2 is filled, the pressurization tubing 6 allows pressure to be transferred from the mainline pipe 1 to the pressure vessel 2 (minus a small change due to friction and any height differences). The connection between the pressurization line 6 and the pressurization port 6a, and the connection between the pressurization line 6 and the pressure vessel 2, is airtight.

This maximises the pressure transfer between the mainline 1 and the pressure vessel 2 and reduces (or potentially eliminates) build-up of air inside the pressure vessel 2. Preferably, the pressurization line 6 comprises a hose or tube of at least 0.5 inches in diameter, to reduce pressure loss in the pressurization line 6.

As described below, the transferred pressure is exerted on the first compartment 3 (and therefore on the first liquid 3a inside the first compartment 3). In other words, the first conduit 6 is coupled to the second compartment 2 for fluid flow between the main conduit 1 and the second compartment 2, for transfer of pressure from the second liquid 3b inside the main conduit 1 to exert a corresponding pressure on the first compartment 3 (and therefore on the first liquid 3a inside the first compartment 3) Pressure transfer assembly provided within a pressure vessel The pressure vessel 2 is used to contain pressurised fluid 3b (for example, up to a pressure equivalent to the maximum possible mains pressure in the main conduit 1, plus a 25% safety factor) without leakage. The pressure vessel 2 contains the two liquids 3a, 3b separated by an impervious pressure-transmitting barrier On this example, the wall of the injection fluid reservoir 3), thus forming a first compartment 3 (containing the first liquid 3a) separated from a second compartment 2 (containing the second liquid 3b). In an illustrative example, the second liquid 3h is water pressurised by the pressure in the mainline pipe 1 (pressurised fluid 3b), whilst the first liquid is the injection fluid 3a (e.g. comprising chlorine). The pressure vessel 2 contains one port 6b for a hydraulic connection 6 between the pressurised fluid 3b and the mainline pipe 1, and one port 4 to maintain a hydraulic connection between the injection fluid 3a and the injection port 5a of the pressure reduction geometry 5.

The pressure vessel 2 has airtight connections which pass through the vessel and allows the injection line 10 to connect to the injection reservoir 3 (via the port 4).

In other words, the first compartment 3 and the second compartment 2 are arranged for transfer of pressure from the second liquid 3b inside the second compartment 2 to exert a corresponding pressure on the first liquid 3a in the first compartment 3.

In more detail, by virtue of the pressure-transmitting deformable barrier between the second compartment 2 and the first compartment 3, pressure is transferred from the second liquid 3b in the second compartment 2 to the first liquid 3a in the first compartment 3.

Considering the system as a whole, and as described above, the flow of the first liquid into the second liquid is driven by the effect of the second liquid flowing through the pressure reduction geometry 5, giving a local reduction in pressure at the low-pressure point, which draws in the first liquid. The reduction in pressure is in proportion to the flow rate of the second liquid along the main conduit and through the pressure reduction geometry 5, and thus the flow of the first liquid into the second liquid is dependent on the flow rate of the second liquid.

However, in the present system, the flow of the first liquid into the second liquid is not exclusively dependent on the flow rate of the second liquid. Rather, to also account for variations in pressure of the second liquid flowing along the main conduit (as such variations would also affect the total dose of the first liquid in the second liquid), the pressure of the second liquid is also used to control the amount of the first liquid that is dispensed into the second liquid.

More particularly, the amount of the first liquid that is drawn into the second liquid depends on the difference between the pressure of the second liquid at the low-pressure point and the pressure of the first liquid at the injection port 5a. The pressure of the first liquid at the injection point 5a is in turn affected by the pressure of the second liquid in the second compartment 2 due to the effect of the pressurization line 6, effectively in the manner of feedforward control.

Accordingly, by taking into account both the flow rate and the pressure of the second liquid flowing along the main conduit, the accuracy of the dispensed dose of the first liquid is improved.

In the illustrated example of Figure 1, the outer wall of the second compartment 2 is also the outer wall of the pressure vessel as a whole. However, this need not necessarily be the case Examples of how the pressure vessel 2 may be constructed include: Pipe with sealed flange: Seal a plastic pipe at one end and install an open flange connection at the other end. A lid is then bolted to the open flange. This lid is used for the hydraulic connection ports.

Moulded plastic pressure vessel: Blow mould or rotation mould a thin-walled plastic pressure vessel with either a built-in lid, or neck which connects to a custom-built lid.

Cast metal pressure vessel: Cast a pressure vessel out of metal in two halves and weld the two halves together.

Injection reservoir The injection reservoir 3 (or 'first compartment') is a deformable (e.g. collapsible or flexible) container that holds the injection fluid 3a inside the pressure vessel 2. The injection reservoir 3 is 'deformable' such that it allows the pressurised fluid (second liquid) 3b to pressurise the injection fluid (first liquid) 3a. The injection reservoir 3 contains a connection to the injection line 10 (via the port 4) to allow the injection fluid 3a to flow to the main pipeline 1.

The deformation of the injection reservoir 3 is repeatable (e.g. elastically reversible) and ensures that the injection reservoir 3 does not become blocked.

Examples of how the injection reservoir 3 may be constructed include: i) A flexible cylindrical bag (as illustrated in Figures 1 to 3) made from plastic film/sheet, or any other suitable material. This may be RE welded, heat welded, or bonded together. Connectors, e.g. BSP threaded connectors, can be welded or bonded into the bag itself. In other words, the first compartment 3 comprises a deformable bag.

ii) Fluids are separated using a diaphragm 11 (as illustrated in Figure 4). The pressurised fluid (second liquid) 3b and injection fluid (first liquid) 3a are separated by a diaphragm 11 which stretches as the injection reservoir 3 fills and empties. The material is preferably chosen such that the energy absorbed as the diaphragm 11 stretches is small relative to the pressure 'energy' that is to be transferred across the diaphragm 11. In other words, the pressure transfer assembly comprises a deformable diaphragm 11, separating the first compartment 3 which contains the first liquid 3a from the adjacent second compartment 2 which contains the second liquid 3b.

iii) Injection fluid 3a is contained within bellows 12 (illustrated in Figure 5) which are connected to the injection line 10. Pressure is exerted on the surface of the bellows 12 by the pressurised fluid 3a. The bellows 12 collapse as they empty, and so the pressure reservoir 2 gradually fills with pressurised fluid 3b. In other words, the first compartment comprises a deformable bellows 12.

iv) Injection fluid is contained within a rubberized 'balloon' 13 (illustrated in Figure 6). The 'balloon' 13 is roughly the volume of the pressure vessel 2 but expands slightly when filled with the injection fluid 3a. The material is preferably chosen so that the energy absorbed as the 'balloon' 13 stretches is small relative to the pressure 'energy' that is to be transferred to the injection fluid 3a. In other words, the first compartment comprises a deformable balloon 13. The 'balloon' 13 may also be referred to as a 'bladder'.

v) The injection fluid 3a is contained within a number of collapsible tubes 14 which are connected in parallel (illustrated in Figure 7). The tubes 14 may be constructed, for example, out of Layflat hose with sealed ends, or any other suitable material. The tubes 14 collapse simultaneously (or substantially simultaneously), and the outlet of the tubes 14 are all fed into the injection tube 10 in parallel. In other words, the first compartment is divided into a plurality of sub-compartments 14, wherein each sub-compartment 14 is configured for containing a respective reservoir of the first liquid 3a, and wherein each sub-compartment 14 is coupled to the second conduit 10 for flow of the first liquid 3a into the second conduit 10. Whilst the sub-compartments shown in Figure 7 are described as tubes 14, each of the sub-compartments 14 may comprise a deformable bellows, deformable balloon or deformable bag.

It will be appreciated that, in the examples of Figures 1-3 and 5-7, the first compartment 3 is disposed inside the second compartment 2, such that the first compartment 3 is compressed inwardly by the effect of the second compartment 2 as the first compartment 3 gradually empties.

On the other hand, in the diaphragm-based example of Figure 4, the first compartment 3 is adjacent to the second compartment 2. Other configurations are possible in which the first and second compartments 3, 2 are adjacent to one another -e.g. by arranging them either side of a piston, such that the piston transfers pressure from the second liquid 3b inside the second compartment 2 to the first liquid 3a in the first compartment 3.

Injection hose In the present illustrative examples, the injection hose 10 (also referred to as the 'injection line', or 'second conduit') is a thin diameter (e.g. < 2mm) hose which connects the injection reservoir 3 to the injection port 5a. However, any other suitable conduit between the injection reservoir 3 and the injection port 5a could be used. The injection fluid 3a flows through the injection hose 10 and into the main pipeline 1. The tubing diameter is small to induce a large pressure drop as the fluid 3a flows through the hose 10. This ensures the flow rate through the hose 10 is low and reduces the dosing ratio to an appropriate value (depending on the dose required).

The injection hose 10 is preferably connected using airtight hose connectors, such as a barbed hose connector, suitable for a small diameter hose.

Injection port The injection port 5a is a hydraulic connection between the injection hose 10 and the low-pressure point of the pressure reduction geometry 5.

Implementational example: valve configuration Figure 2 shows a modified version of the dosing apparatus 100 of Figure 1, in which additional valves are provided. The modifications of Figure 2 may also be applied to any of Figures 4-7.

The provision of at least a first air release valve 8a is advantageous since trapped air in the system 100 (e.g. in the pressure vessel 2 or in the reservoir 3 of injection fluid 3a) can be compressed, which would interfere with the pressure transference mechanism that drives the dosing. This interference would make the delivered dose less accurate and more variable.

The provision of at least one pressure relief valve is advantageous, since if the apparatus 100 is operated above the safe operating pressure, the vessel may potentially fail catastrophically through leaking or bursting.

In under-resourced contexts, it can be difficult to measure pressure accurately, or to diagnose reasons why the dosing apparatus is not operating in an optimal way.

Therefore, the addition of the air release valve(s) 8a and pressure relief valve(s) is advantageous, since they improve the overall accuracy, reliability and safety of the dosing apparatus 100.

The dosing apparatus 100 illustrated in Figure 2 includes, among other features: valves to control the transfer of pressure throughout the system; an air release valve 8a to release air from the system; and a refill system 9 and corresponding refill valve 9a for refilling the injection reservoir 3.

A pressurization valve 70 is provided for control of the hydraulic connection 6 between the main conduit 1 and the pressure vessel 2. The pressurization valve 70 can be placed at either end of the pressurization line 6 (or mid-way along the pressurization line 6, as illustrated in Figure 2). The valve 70 may be, for example, a ball valve or gate valve. The pressurization valve 70 allows the user to cut off the pressure in the pressure vessel 2 to allow the injection reservoir 3 to be refilled.

In other words, the dosing apparatus 100 comprises a valve 70 for selectively allowing flow of the second liquid 3b along the first conduit 6. The valve 70 selectively allows pressure to be transferred from the second liquid 3b inside the main conduit 1 to the second liquid 3b inside the second compartment 2 (and subsequently to the first compartment 3 and the first liquid 3a inside the first compartment 3).

An injection line valve 7 (also referred to as a 'dosing valve') is provided for controlling the hydraulic connection 10 between the injection reservoir 3 and the injection port 5a of the pressure reduction geometry 5. The injection line valve 7 can be placed at any suitable location along the injection line 10. One option for the valve 7 is to use an on/off valve such as a ball valve or gate valve to stop/start the flow of the injection fluid 3a. Another option is to use a valve 7 with a variable pressure drop, such as a needle valve, which advantageously allows a user to control the flow rate of the injected fluid 3. A further option is for valve 7 to comprise a needle valve and a ball valve in series, with the needle valve being used to provide fine control over the flow rate, and the ball valve being used to start/stop the flow of the injection fluid 3a, without disrupting the position in which the needle valve has been set. Some examples of use of such valve(s) include: Controlling the flow rate of the injected fluid 3a into the motive fluid 3b - Stopping/starting the flow of the injected fluid 3a into the motive fluid 3b Stopping the hydraulic connection 10 between the injection point and the injection reservoir 3, to allow the reservoir 3 to be refilled In other words, the dosing apparatus 100 comprises a dosing valve 7 for selectively allowing flow of the first liquid 3a along the second conduit 10 to mix with the second liquid 3a in the main conduit 1.

A pressure vessel release valve 8b is provided as a port at the top of the pressure reservoir 2 and can be opened to atmosphere. This allows air to be released from the pressure vessel 2. The pressure vessel release valve 8b may be provided, for example, as a ball valve or similar which manually opens to allow air to be released during periodic maintenance. Alternatively, an air vent may be provided which can be opened manually or automatically to release the air through periodic maintenance.

Examples of when the pressure vessel release valve 8b might be used include: When air gets into the system through the pipework or during the refill process To relieve pressure from the pressure vessel 2 before the injection reservoir 3 is refilled In other words, the dosing apparatus 100 comprises a second air-release valve 8b that is coupled to the second compartment 2 for releasing air from the second compartment 2.

The pressure vessel 2 may also be coupled to a pressure relief valve, which may be provided either as the pressure vessel release valve 8b described above, or as a separate valve. The pressure relief valve may be configured to open, to allow fluid to flow out of the pressure vessel 2, when the pressure inside the pressure vessel exceeds a threshold level 2.

In other words, the dosing apparatus 100 comprises a pressure release valve that is coupled to the second compartment 2 for releasing second liquid 3b from the second compartment 2 when the pressure of the second liquid 3b inside the second compartment 2 exceeds a threshold level.

An injection reservoir air release valve 8a is provided as a port at the top of the injection reservoir 3 that can be opened to atmosphere. This allows air to be released from the injection reservoir 3. This injection reservoir air release valve 8a may be provided as a ball valve (or similar) which manually opens to allow air to be released during periodic maintenance. Alternatively, an air vent could be provided, which can be opened manually to release the air through periodic maintenance, or an automatic air vent could be provided to allow the air to be released gradually as it builds up.

Examples of when the injection reservoir air release valve 8a may be used include: To release air that enters the injection reservoir 3 during the refill process To release air that build up in the injection reservoir 3 during operation In other words, the dosing apparatus 100 comprises a first air-release valve 8a that is coupled to the first compartment 3 for releasing air from the first compartment 3.

In the example illustrated in Figure 2, the air-release valves 8a and 8b are provided on the upper surface of the vessel 2. By virtue of the provision of the first air-release valve and the second air-release valve on the upper surface of the vessel, a more compact dosing apparatus can be provided. Moreover, when the first air-release valve and the second air-release valve are provided on the upper surface, the air can be more reliably extracted from the first and second compartments.

An injection refill valve 9a is provided for refilling the injection reservoir 3 with the injection fluid (first liquid) 3a. The injection refill valve 9a may comprise a ball valve (or similar) which can be connected to an external source 9 ('refill system') of the injection fluid 3a to allow the injection reservoir 3 to be refilled. When the valve 9a is opened, the injection fluid 3a can flow into the injection reservoir 3. The valve 9a is closed during operation of the dosing apparatus 100 to dispense the injection fluid 3a into the main conduit 1.

An exemplary method of the refilling (or filling) the first compartment 3 with the first liquid 3a is set out below: The pressurization valve 70 is closed to isolate the pressure vessel 2 from the mainline 1.

2. The injection valve 7 is closed to isolate the injection reservoir 3 from the mainline 1.

The pressure vessel pressure release valve 8b is opened to equalize the pressure inside the pressure vessel 2 with atmosphere.

4. The refill valve 9a is opened to allow injection fluid 3a (from an external source 9) to flow into the injection reservoir 3. This flow can be induced in a number of

ways, for example:

a. Placing the external source of injection fluid 3a above the injection reservoir 3 and allowing the injection fluid 3a to flow into the injection reservoir 3 under the influence of gravity.

b Pumping from the external source using an electronic pump (e.g. a low-power electronic pump).

c. Pumping from the external source using a hand pump (advantageously, the use of a hand pump does not require electricity).

The injection reservoir air release valve 8a is opened to release any air that has built up during the refill process.

6. The refill valve 9a, injection reservoir air release valve 8a, and the pressure vessel pressure release valve 8b are closed.

7. The pressurization valve 70 and the injection valve 7 are opened.

In other words, the dosing apparatus comprises a refill valve 9a that is coupled to the first compartment 3 and is configurable to allow a flow of the first liquid 3a into the first compartment 3. The refill valve 9a is operable by a user to manually fill the first compartment 3 with the first liquid 3a (e.g. using the hand pump).

Figure 3 shows a modification of the dosing apparatus of Figure 2, in which a non-return valve 15 (also referred to as a 'one-way valve' or 'check valve') is additionally provided. This valve 15 only allows fluid to flow through it in one direction. It is used to ensure that the injection fluid 3a can flow into the main pipeline 1, but that the fluid in the main pipeline 1 cannot flow back into the injection reservoir 3 via the injection line 10.

In other words, the second conduit 10 comprises a one-way valve 7 configured for preventing flow of fluid from the main conduit 1 into the first compartment 3.

The modification of Figure 3 may also be applied to any of Figures 4-7.

Additional clauses The present invention also relates to the numbered clauses set out below.

The present invention relates to a venturi-based dosing apparatus 100 with a pressure feedback mechanism configured to dispense a first liquid 3a into a second liquid 3b, at a dose (e.g. concentration or ratio) that is independent of the pressure and flow rate of the second liquid 3b inside a main conduit 1.

Clause 1: A dosing system for dosing one liquid (an auxiliary fluid or 'first liquid') into a pipe containing another liquid (the main fluid or 'second liquid') comprising: a pressure vessel divided in a fluid-tight manner by means of a closed bag into an auxiliary compartment within the bag which is in fluidic communication via a first port with an eductor which sits within the pipe, and a main fluid compartment surrounding said bag which is in fluidic communication via a second port with the pipe containing the main fluid such that the pressure within the pipe is transferred through the liquid and through the closed bag into the auxiliary fluid, a check valve within the fluid line between the closed bag and the Venturi low pressure section, a pressure relief valve for the pressure vessel and air release valves for the auxiliary compartment and the main fluid compartment.

Advantageously, the pressure transference from the main fluid to the closed bag means that the pressure difference between the auxiliary fluid and eductor is constant, and thus the dosage is independent of pressure as well as flow rate.

The system also includes a pressure relief valve to protect the system from pressure surges or high pressures. The system also includes air release valves to remove any air in the system which would interfere with the pressure transference mechanism. The system also includes a check valve or similar component to prevent fluid from the main pipe entering the flexible bag.

The system requires no electricity and is, advantageously, much simpler than other mechanical dosing systems.

Clause 2: A dosing system as in Clause 1 wherein said eductor comprises a Venturi. Advantageously, fabrication of the Venturi is simple and inexpensive.

Clause 3: A dosing system as in Clause 1 wherein the first and second port contain valves to selectively turn on or off fluid flow and/or pressure transference.

Advantageously, the provision of the valves to selectively turn on or off fluid flow and/or pressure transference enables ease-of-use within installation and maintenance.

Clause 4: A dosing system as in Clause 1 wherein the main fluid compartment and auxiliary compartment each contain a port in fluid communication with an air release valve.

Advantageously, the air release valve allows air within the system to be released, so as to avoid air compression interfering with the pressure transference between 30 compartments.

Clause 5: A dosing system as in Clause 1 wherein the auxiliary compartment contains a port in fluidic communication with a refill system which allows this compartment to be refilled when required.

The space between the first port (in the auxiliary compartment) and the eductor may be referred to as a 'chlorine injection line', within which there is preferably tubing. The diameter and length of this tubing may be adjusted, which in turn adjusts the pressure losses through the tubing. The pressure losses within this tubing determine the dosage the system provides. The higher the pressure losses, the lower the auxiliary fluid to main fluid ratio (dose).

Clause 6: A dosing system as in Clause 1 wherein tubing between the first port and eductor has an adjustable pressure loss achieved by varying the length or diameter of the tubing, thus allowing the dose achieved by the system to be adjusted.

Clause 7: A dosing system as in Clause 1 wherein the first port contains a two-way valve to switch this port between this compartment being in fluidic communication with the pipe containing the main fluid or this compartment being in fluidic communication with a refill system which allows this compartment to be refilled when required.

By virtue of the two-way valve, the probability of user error is decreased (e.g. leaving all of the valves in an open position).

Clause 8: A dosing system as in Clause 1 wherein tubing between the first port and eductor has an adjustable pressure loss achieved by introducing mechanisms and components of a known pressure loss into the tubing; components and mechanisms include but are not limited to orifice plates, valves (e.g. needle valves or butterfly valves), expansions and contractions. This adjustable pressure loss allows an adjustable dose to be achieved by the system.

Clause 9: A dosing system for dosing one liquid (an auxiliary fluid) into a pipe containing another liquid (the main fluid) comprising: a pressure vessel divided in a fluid-tight manner by means of a deformable diaphragm into an auxiliary compartment which is in fluidic communication via a first port with an eductor which sits within the pipe, and a main fluid compartment which is in fluidic communication via a second port with the pipe containing the main fluid such that the pressure within the pipe is transferred through the liquid and through the diaphragm into the auxiliary fluid, a check valve within the fluid line between the closed bag and the Venturi low pressure section, a pressure relief valve for the pressure vessel and air release valves for the auxiliary compartment and the main fluid compartment.

Clause 10: A dosing system for dosing one liquid (an auxiliary fluid) into a pipe containing another liquid (the main fluid) comprising: a pressure vessel divided in a fluid-tight manner by means of an expandable bellows into an auxiliary compartment within the expandable bellows which is in fluidic communication via a first port with an eductor which sits within the pipe, and a main fluid compartment surrounding said expandable bellows which is in fluidic communication via a second port with the pipe containing the main fluid such that the pressure within the pipe is transferred through the liquid and through the expandable bellows into the auxiliary fluid, a check valve within the fluid line between the expandable bellows and the Venturi low pressure section, a pressure relief valve for the pressure vessel and air release valves for the auxiliary compartment and the main fluid compartment.

Clause 11: A dosing system for dosing one liquid (an auxiliary fluid) into a pipe containing another liquid (the main fluid) comprising: a pressure vessel divided in a fluid-tight manner by means of an expandable balloon into an auxiliary compartment within the expandable balloon which is in fluidic communication via a first port with an eductor which sits within the pipe, and a main fluid compartment surrounding said expandable balloon which is in fluidic communication via a second port with the pipe containing the main fluid such that the pressure within the pipe is transferred through the liquid and through the expandable balloon into the auxiliary fluid, a check valve within the fluid line between the expandable balloon and the Venturi low pressure section, a pressure relief valve for the pressure vessel and air release valves for the auxiliary compartment and the main fluid compartment.

Clause 12: A dosing system for dosing one liquid (an auxiliary fluid) into a pipe containing another liquid (the main fluid) comprising: a pressure vessel divided in a fluid-tight manner into multiple compartments comprising one compartment for the main fluid and a plurality of compartments for the auxiliary fluid, wherein the plurality of compartments for the auxiliary fluid are in fluidic communication via a first port with an eductor which sits within the pipe, and the compartment for the main fluid is in fluidic communication via a second port with the pipe containing the main fluid such that the pressure within the pipe is transferred through the liquid, through the plurality of compartments for the auxiliary fluid and into the auxiliary fluid; a check valve within the fluid line between the plurality of compartments for the auxiliary fluid and the Venturi low pressure section; a pressure relief valve for the pressure vessel; and air release valves for the plurality of compartments for the auxiliary fluid and the compartment for the main fluid.

Clause 13: A dosing system as in Clause 12 wherein the compartment for the main fluid and/or the plurality of compartments for the auxiliary fluid are formed by bellows, balloons or bags.

Modifications and alternatives As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above examples and variations whilst still benefiting from the inventions embodied therein.

As described above, Figures 2 and 3 show modifications of the dosing apparatus 100 of Figure 1 in which a number of additional valves and other features are provided. Each of these additional valves and other features (e.g. the pressurization valve 70, the injection reservoir air release valve 8a, the pressure vessel release valve 8b, the injection line valve 7, the refill system 9, and the one-way valve 15) may be incorporated either individually, or in any suitable combination, into the dosing apparatus 100 illustrated in Figure 1. Similarly, these additional valves and other features may be incorporated either individually, or in any suitable combination, into the dosing apparatus 100 illustrated in any of Figures 4 to 6 (which show various examples of ways in which the first compartment 3 may be provided).

The injection refill valve 9a and the injection line valve 7 may be provided as a single valve. In other words, the dosing apparatus 100 may comprise a configurable valve that is configurable between: a first configuration for allowing a flow of the first liquid 3a into the first compartment 3, and for preventing a flow of the first liquid 3a from the first compartment 3 and into the flow of the second liquid 3b inside the main conduit 1; and a second configuration for allowing a flow of the first liquid 3a from the first compartment 3 and into the flow of the second liquid 3b inside the main conduit 1, and for preventing a flow of the first liquid 3a into the first compartment 3 (e.g. via the refill system 9).

VVhilst in some examples the first liquid 3a has been described as comprising a chlorine solution and the second liquid has been described as comprising water, any other suitable liquids may be used. For example, the first liquid 3a may comprise a fertiliser and the second liquid 3b may comprise water.

Whilst in the examples shown in Figures 1 to 7 the pressure reduction geometry 5 comprises a Venturi, any other suitable apparatus for drawing fluid from the injection reservoir 3 into the main conduit 1 to provide a constant dose could alternatively be provided.

Each of the valves illustrated in Figure 2 or Figure 3 may be operated manually by a user. Alternatively, one or more of the valves may be operated under the control of a suitable controller, such as an analogue or digital controller.

In the examples of Figures 1-3 and 5-7 described above, the first compartment 3 is disposed inside the second compartment 2, such that the first compartment 3 is compressed inwardly by the effect of the second compartment 2 as the first compartment 3 gradually empties. Alternatively, however, configurations may be envisaged in which the second compartment 2 is disposed inside the first compartment 3, such that the first compartment 3 is compressed outwardly by the effect of the second compartment 2 as the first compartment 3 gradually empties.

Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

Claims

CLAIMS1. Dosing apparatus for dispensing a first liquid into a flow of a second liquid inside a main conduit, the dosing apparatus comprising: a pressure transfer assembly comprising a first compartment configured for containing a reservoir of the first liquid, and a second compartment configured for containing a reservoir of the second liquid; a first conduit for fluid flow, wherein the first conduit is coupled to the second compartment for fluid flow of the second fluid between the main conduit and the second compartment, wherein the first compartment and the second compartment are arranged for transfer of pressure from the second liquid inside the second compartment to exert a corresponding pressure on the first liquid in the first compartment; means for drawing the first liquid from the first compartment and into the flow of the second liquid inside the main conduit as the second liquid flows along the main conduit, the drawing being driven by the flow of the second fluid along the main conduit; and a second conduit for fluid flow, for fluid flow from the first compartment to the means for drawing the first liquid from the first compartment; wherein the second conduit comprises a one-way valve configured for preventing flow of fluid from the main conduit into the first compartment; wherein the dosing apparatus comprises a pressure release valve that is coupled to the second compartment for releasing second liquid from the second compartment when the pressure of the second liquid inside the second compartment exceeds a threshold level; wherein the dosing apparatus comprises a first air-release valve that is coupled to the first compartment for releasing air from the first compartment; and wherein the dosing apparatus comprises a second air-release valve that is coupled to the second compartment for releasing air from the second compartment.
2. The dosing apparatus according to claim 1, wherein the dosing apparatus comprises a refill valve that is coupled to the first compartment and is configurable to allow a flow of the first liquid into the first compartment.
3. The dosing apparatus according to claim 2, wherein the refill valve is operable by a user to manually fill the first compartment with the first liquid.
4. The dosing apparatus according to any preceding claim, wherein the means for drawing the first liquid from the first compartment comprises an eductor.
5. The dosing apparatus according to any preceding claim, wherein the means for drawing the first liquid from the first compartment comprises a Venturi.
6. The dosing apparatus according to any preceding claim, wherein the first liquid comprises a chlorine solution and the second liquid comprises water.
7. The dosing apparatus according to any one of claims 1 to 5, wherein the first liquid comprises a fertiliser and the second liquid comprises water.
8. The dosing apparatus according to any preceding claim, wherein at least one of the first air-release valve and the second air-release valve are provided on an upper surface of the pressure transfer assembly.
9. The dosing apparatus according to any preceding claim, wherein the dosing apparatus comprises a dosing valve for selectively allowing flow of the first liquid along the second conduit to mix with the second liquid in the main conduit.
10. The dosing apparatus according to any preceding claim, wherein the dosing apparatus comprises a valve for selectively allowing flow of the second liquid along the first conduit.
11. The dosing apparatus according to any preceding claim, wherein the dosing apparatus comprises a valve for selectively allowing pressure to be transferred from the liquid inside the main conduit to the liquid inside the second compartment.
12. The dosing apparatus according to any preceding claim, wherein the dosing apparatus comprises a configurable valve that is configurable between: a first configuration for allowing a flow of the first liquid into the first compartment from an external reservoir, and for preventing a flow of the first liquid from the first compartment and into the flow of the second liquid inside the main conduit; and a second configuration for allowing a flow of the first liquid from the first compartment and into the flow of the second liquid inside the main conduit, and for preventing a flow of the first liquid into the first compartment from the external 30 reservoir.
13 The dosing apparatus according to any preceding claim, wherein at least one of a length or diameter of the second conduit is configured for dispensing a predetermined amount of the first liquid into the second liquid inside the main conduit, per unit volume of second liquid that flows along the main conduit.
14. The dosing apparatus according to any preceding claim, wherein the second conduit is configured to induce a predetermined pressure loss between the first compartment and the main conduit, for dispensing a predetermined amount of the first liquid into the second liquid inside the main conduit, per unit volume of second liquid that flows along the main conduit.
15. The dosing apparatus according to claim 14, wherein the second conduit comprises at least one of an orifice plate, valve, expansion, or contraction for inducing the predetermined pressure loss between the first compartment and the main conduit
16. The dosing apparatus according to any preceding claim, wherein the first compartment comprises at least one of a deformable bag, a deformable bellows, or a deformable balloon.
17. The dosing apparatus according to any preceding claim, wherein the first compartment is disposed inside the second compartment.
18. The dosing apparatus according to any of claims 1 to 15, wherein the pressure transfer assembly comprises a deformable diaphragm between the first compartment and the second compartment.
19. The dosing apparatus according to any of claims 1 to 15 or 18, wherein the first compartment is adjacent to the second compartment.
20. The dosing apparatus according to any preceding claim, wherein the first compartment is divided into a plurality of sub-compartments, wherein each sub-compartment is configured for containing a respective reservoir of the first liquid, and wherein each sub-compartment is coupled to the second conduit for flow of the first liquid into the second conduit.
21. The dosing apparatus according to claim 20, wherein each of the sub-compartments comprises a deformable bellows, deformable balloon or deformable bag.
22. The dosing apparatus according to any preceding claim, wherein the dosing apparatus does not require the use of electricity in order to dispense the first liquid into the flow of the second liquid inside the main conduit.
23. The dosing apparatus according to any one of claims 2 to 22, wherein the dosing apparatus does not require electricity in order to fill the first compartment with the first liquid via the refill valve.
24. The dosing apparatus according to any preceding claim, wherein at least one of the main conduit, the first conduit or the second conduit comprises a tube or pipe.
25. Dosing apparatus for dispensing a first liquid into a flow of a second liquid inside a main conduit, the dosing apparatus comprising: a pressure transfer assembly comprising a first compartment configured for containing a reservoir of the first liquid, and a second compartment configured for containing a reservoir of the second liquid; a first conduit for fluid flow, wherein the first conduit is coupled to the second compartment for fluid flow of the second fluid between the main conduit and the second compartment, wherein the first compartment and the second compartment are arranged for transfer of pressure from the second liquid inside the second compartment to exert a corresponding pressure on the first liquid in the first compartment; means for drawing the first liquid from the first compartment and into the flow of the second liquid inside the main conduit as the second liquid flows along the main conduit, the drawing being driven by the flow of the second fluid along the main conduit; and a second conduit for fluid flow, for fluid flow from the first compartment to the means for drawing the first liquid from the first compartment.
26. The dosing apparatus according to claim 25, wherein the second conduit comprises a one-way valve configured for preventing flow of liquid from the main conduit into the first compartment.
27. The dosing apparatus according to claim 25 or claim 26, wherein the dosing apparatus comprises at least one of: a pressure release valve that is coupled to the second compartment for releasing second liquid from the second compartment when the pressure of the second liquid inside the second compartment exceeds a threshold level; a first air-release valve that is coupled to the first compartment for releasing air from the first compartment; and/or a second air-release valve that is coupled to the second compartment for releasing air from the second compartment.
28. A method of dispensing a first liquid into a flow of a second liquid inside a main conduit using the dosing apparatus according to any preceding claim.