Aerosol Dispenser This invention relates to an aerosol dispenser.
It is known to provide an aerosol dispenser comprising a container or canister in which a product is stored under pressure. A valve is provided to enable the product to be dispensed from the container when the valve is opened. The product to be dispensed wilJ often be a liquid, such as a liquor for example, and a propellent will also be present in the canister at lea it partly as a compressed gas. Some propellants, such as butaae, are present partly as a gas and partly as a liquid, which may be in solution in the liquid product Other propellents, such as compressed air or nitrogen, are present only ;is a gas whilst with propellants such as carbon dioxide a limited amount of the gas may be held in suspension in a liquid In certain aerosol dispensers, the li quid is held in a flexible bag within the. canister and so is separated from the propellant
A nozzle is often fitted to the outlet valve by means of a valve stem to ensure the product is delivered in an appropriate form and direction for the application. Many aerosols have an atomising nozzle fitted to the outlet valve, the nozzle being configured to cause the liquid stream passing through the nozzle under pressure to break up or "atomise" into numerous droplets as it
passes through an outlet orifice of the nozzle to form an. atomised spray or mist
i A. large number of commercial products are presented to consumers in mis
form, including, for example, antiperspirant sprays, de-odorant sprays, perfumes, air fresheners, antiseptics, paints,' insecticides, polish, hair care products, pharmaceuticals, water and lubricants.
The optimum size of the droplets required in me spray dcpe ads primarily on the particular product concerned and the application for which ~t is intended. For example, a pharmaceutical spray that contains a drug intended to be inhaled by a patient (e.g. an asthmatic patient) usually requires very small droplers, which can penetrate deep into the lungs. In contrast, a polish spray preferably
CONFIRMATION COPY

comprises spray droplets with, larger diameters to promote the impaction of the aerosol droplets on the surface that is to be polished and, particularly if the spray is toxic, to reduce the extent of inhalation.
The size of the aerosol droplets produced by conventional nozzle arrangements is dictated by a number of factors, including the dimensions of the outlet orifice and the pressure with which the fluid is forced through the nozzle, However, problems can arise if it is desired to produc e a spray that comprises small droplets with a narrow droplet size distribution, particularly at low pressures. The use of low pressures for generating spray; is becoming increasingly desirable because it enables the quantity of propel ant present in the spray to be reduced or alternative propellants which produce lower pressures, such as compressed air, to be used. The problem of providing a high quality spray at low pressures is further exacerbated if the fluid concerned has a high viscosity became it becomes harder to atomise the fluid into sufficiently small droplets.
A farther problem with known pressurised aerosol dispensers fitted with conventional valve and nozzle arrangements is that the size of the aerosol droplets generated tends to increase during the lifetime of the aerosol dispenser, particularly towards the end of tie dispenser's life as the pressure within the canister reduces as the contents become gradually depleted. This reduction in pressure causes an observable increase in the size of the aerosol droplets generated and thus, die quality of the spray produced is comprormised.
The amount by which the pressure drops over the life of the dispenser varies depending on the type of propellent used. Where me propellent, such as butane, exists in the canister both as a liquid and a gas, the reduction in pressure over the life of the dispenser may be 20-30%. With this type of pitipellant, more gas comes out of solution as the product is used up and the pressure in the canister drops. By comparison, with propellauis that are present mainly or
exclusively as a compressed gas, me overall reduction in pressure may be 50% or more.
To assist in the break up of droplets and improve atormisation some known aerosol dispenser valves arc provided with one or more fine holes in the housing of the valve through which the propellant gas can be bled into the liquid product as it is dispensed through the valve. These holes a re known as a vapour phase tap (VPT).
A problem with the use of a VPT is that the propellant gas is used up more quickly, exacerbating the problems discussed above in regard to the loss of pressure in the canister over the life of the dispenser. This is a problem regardless of me propellant used but is a particular problem where the propellant is a compressed gas, such as air or nitrogen, when the loss of pressure may result in an unacceptable performance as the contents become depleted For example, in a typical dispenser without a VPT and which uses compressed air as the propellant, the starting pressure will be around 10 bar reducing to around 4 bars. However, if a VPT is used, the pressure may fall to less than 2 bars, which is insufficient to atomise the liquid.
• For the purposes of atomisation of the liquid product, it is preferable if the VPT produces a higher ratio of propellant gas to liquid when the pressure in the canister is lower than when the canister is full and the pressure is higher. This is because at the higher pressures, the relatively high rate of flow of the liquid through the nozzle is sufficient on its own to cause the required atoinisation without the need to introduce propellant gas into the liquid stream through the VPT. However, with a conventional VPT, the opposite effect is seen as the ratio of propellant gas' to liquid falls as the pressure in the canister falls. This can be explained by considering the flow through the "VPT. The gas flows through the VPT because the liquid flowing through the housing is at a lower pressure than the gas on the outside of me housing and the rate at which

the gas flows through the VPT is a function cross sectional area of the VPT and the pressure difference across it Because the cross sectional area of the VPT is fixed, the volumetric flow rate through the VPT reduces as the pressure in the canister falls.
In order to ensure that sufficient gas is hied into the liquid to provide for proper atoimsation of the liquid when the pressure in the canister has reduced towards the end of the life of the dispenser, the VPT openings have to be a certain minimum size. However, this means that excess propel] ant gas is bled into the liquid when the canister is full and the pressure is higher. It cart be seen, therefore, that with a conventional VFT a considerable amount of the propellent gas bled through the VPT when the canister is relatively full is wasted, as it is not essential for ensuring propel atomisation of the liquid. This problem is further compounded because the propellant gas is compressible and hence for a given volumetric flow rate, a greater mass of gas will pass through the VPT when the canister is full and is at its highest pressure inan when the canister is nearly empty and the pressure inside the canister has dropped.
Varying the manner in which the gas is delivered into fee valve housing thorough a VPT has been found to make a significant difference to the droplet size and to the spray form of the aerosol It has been found in particular (hat several small holes give better results than one large hole. How ever, there are difficulties in manufacturing small holes. Typically, the valve housing is injection moulded from polymeric materials and the VPT holes are product using pins in the mould. In order to produce smaller holes the size of the pins needs to be reduced but if very fine pus are used they have a tendency to break. A further problem with very small holes is that they can become blocked.
There is a need then to provide an improved aerosol dispenser that overcomes, or at least reduces, the problems of the prior art dispensers.
There is a particular need to provide an improved aerosol dispenser having a VPT, in which, the overall amount of propellent gas bled into the liquid product through the YPT is reduced whilst ensuring adequ ate atomisation of the liquid over the useful life of the dispenser.
In accordance with the invention, there is provided an ae :osol dispenser comprising a canister adapted to contain a liquid product to be d ispensed and a propellant present in the canister at least partly as a gas, said dispenser having a valve for controlling the release of the liquid product from the canister and means for introducing a pardon of the gaseous propellant into the liquid product as it is dispensed, characterised in that the dispenser further comprises a flow control means for varying the rate at which the propellant gas is introduced into the liquid product in dependence cm the pressure of the contents in the canister.
Further optional features of the invention are set out in the dependent claims.
Several embodiments of the invention will now be described, by way of example only, with reference to the following drawings in which:
Figure 1A is a cross-sectional view through a male nerosol valve arrangement forming part of a dispenser in accordance with the invention, showing the valve when closed;
Figure 1B is a view similar to that of Fig. 1A but showing the aerosol valve when open; and
Figures 2 to 27 are various schematic views, some in i ross-sectioa, illustrating different embodiments of a flow control device forming part of a dispenser in accordance with the invention.
Figs. 1A and-1B show a male type aerosol valve 10 forming part of a dispenser in accordance with the invention. The valve 10 has a hollow plastic

housing 11 mounted in a metal cup 12 which forms part of an upper surface of an aerosol canister. As is well known in the art, the aerosol canister will typically contain a liquid product, which may be a liquor, to be dispensed sad a propellent, at least part of which is present as a gas above the product The propellent pressurizes the canister so that the product is dispensed when the valve is opened. Any suitable propellant may be used such as butane, compressed air, nitrogen or carbon dioxide, for example.
A sealing gasket 13 is located in a recess at the upper end of the housing. A valve member 14 is slidably positioned inside the housing and is biased upwardly by means of a spring 15. A valve stem 16 projects up wardly from the valve member and is received in an actuator/nozzle 17. A lower end of the housing provides an inlet 18 to the valve and also mounts a dip tube 19. The valve stem 16 is hollow and a hole 20 is provided at the base of the stem through which fluid can exit the valve housing and enter the stem when the valve is opened,
When the dispenser is not actuated, the valve member is biased by the spring to its upper position, as shown in Fig, 1A, so that the hole 20 is sealed by the gasket and the valve is closed However, when downward pressure is applied to the actuator/nozzle 17, the valve member 14 is moved downwardly in the housing against the bias of the spring, as shown in Fig.1B, so that hole 20 becomes exposed. The product, together with the propellant passes through hole 20 into the stem from where it enters an outlet passage 21 in, the actuator/nozzle before being dispensed in aerosol or spray form from an cutlet orifice 22 of the actuator/nozzle.
To assist with the atomisation of the liquid, a VPT 24 is formed in a side wall of the housing 11 through which the gaseous propellant nbove the liquid product in the canister can be introduced or bled into the liquid product as it passes through the valve 10. The VPT 24 comprises a small hole or opening 26

through fhe side wall of the housing 11 through which fhe gaseous propellant can pass to enter fee liquid product -within the valve housing. The VPT 24 also has a flow control device 28 configured to control the rate at which the gas flows through, the VPT 24 is response to changes in the pressure inside lie canister.
The flow control device 28 comprises a flow control element 30, which is located in 201 enlarged recess or chamber 32 formed tn an out T surface of the wall of the housing 11 about the VPT opening 26, In the present embodiment, the flow control element 30 is in the form of a disc shaped shuttle that moves freely within the recess 32, which is circular. When the valve 10 is open, the element 30 is pressed towards the inner end wall 34 of the recess by the pressure of me gas flowing through the recess 32 so that it restricts the flow of gas through the opening 26, The flow control element is held within the recess by means of an inwardly projecting lip 36 formed about an alter end of the recess, though any suitable means of retaining the element 30 can be used.
The flow control element 30 has a substantially flat inner face 38 which, opposes a corresponding flat face of the inner or downstream end wall 34 of the recess in which, the VPT opening 26 is formed. As shown in Figures 1A and 1B, the outer diameter of the of the flow control element 30 is g reater than that of the VPT opening 26 so that it completely covers the opening and overlaps with at least part of the inner end wall 34. However, by appropriate design and selection of materials, it can be arranged that the flow control dement 30 does not form a perfect seal with the inner end wall 34 such that the propellant gas can pass between the flow control element 30 and the end wall 24 and through the VPT opening 26 in to the valve housing.
The force with which fhe element 30 is pushed towards the end wall 34 is proportional to the pressure difference acting across the opening 26 (i.e. the difference in pressure between the gas oa the outside of the housing and the
liquid product flowing through the housing). When the dispenser is full and the pressure in the canister is at its highest, the pressure differential across the opening win be relatively high and the flow control element 30 is pressed towards the end wall 34 with a correspondingly high force forming a dose partial seal with the lace of the wall and offering a relatively high resistance to the flow of propcllant through the VPT opening 26. As the dispenser empties and the pressure in the canister falls, the pressure differential across the VPT opening 26 when the valve is opened also falls. As a result, the force pushing the flow control element 30 towards the inner ead wall 34 will bis lower and the propellant will be able to pass between the flow control element 30 and the inner end wall 34 more easily. Thus the flow control device 28 offers a greater resistance to the flow of gas through the VPT opening when the pressure in the canister is relatively high than when the pressure in the canister is relatively low.
The flow control means 28 helps to reduce the overall loss of propellant gas through the VPT 24 by restricting the flow of gas when the pressure in the canister is relatively high and there is less need to bled gas intc the liquid to ensure atomisation. However, the device 28 is configured to alow sufficient gas to flow through the VPT when the pressure in the canister has dropped to provide a ratio of gas to liquid sufficiently high as to ensure adequate atomisation of the liquid as it flows through the nozzle. As less gas is lost through the VPT, the overall pressure drop in the canister is also reduced and, by appropriate design, it can be arranged that there is sufficient pressure in the canister to achieve adequate atomisation of the liquid product over the whole useful life of the dispenser or that the useful life is increased,
In the present embodiment, the flow control means 28 is configured so that, over a given range of pressure variation in the canister, the race of flow of gas through the VPT remains fairly constant or at least more so than would be the case without the flow control device 28. However, in practice it may be

sufficient to merely to restrict the flow of gas through theVPT when the pressure in the canister is relatively high so as to reduce wastage of the propellant gas. In a fttriher alternative, the flow control device 28 could be configured so that the flow rate of the gas through, the VPT increases as the pressure in the canister falls. It will be appreciated that a flow .control means can be configured in a number of ways whilst still achieving the objective of reducing the wastage of propellent gas through the VPT. For example, a flow control means could be configured so that the ratio of gas to liquid product dispensed remains generally constant or that the ratio of gas to liquid product increases as the pressure in the canister falls.
In one embodiment, the flow control element 30 and the inter face of the end wall 34 of the recess are made from rigid or a semi-rigid materials such as polypropylene or nylon plastic, metal or ceramic so that the two corresponding flat faces 38, 34 are not able to form a true seal even when they are pressed together by the pressure differential across the opening. However, for certain applications that are required to operate at lower pressure differentials, it may be appropriate to use softer materials as these can form a parti al seal more easily.
To ensure that a complete seal is not formed between the flow control element 30 and the inner race of the end wall 34 of the recess, the corresponding surfaces of the inner end wall 34 of the recess and/or the face 38 of the flow control element 30 may be textured or other means may be provided, to space me flow control element 30 from the inner end wall 34 by a very smidl amount Alternatively, grooves may be formed in the surface of the inner end wall 34 of the recess and/or the face 38 of the flow control element along which the fluid can pass to reach the VPT opening 26.
la certain 'embodiments, at least part of the face 38 of the flow control element 34 will contact the wall 34 whilst fluid is flowing mrough the opening

26. However, in other embodiments, particularly where the faces of the element 38 and the wall 34 are smooth, the fluid flowing between the faces may force them apart by a very small amount. In most cases, the gap between the faces 38, 34 in use will be no more than 0.01mm but in certain, circumstances the gap may be up to a maximum 0.3mm or even up to a maximurn of 0.6mm. It should be appreciated that the spacing between the faces in use is dependant on the pressure differential between the gas outside the valve housing and the liquid inside. Where the pressure differential is high, as will be the case when the canister is full or nearly full, the gap between the faces will be small so that the cross sectional area through which me fluid can flow is correspondingly small As the contents of the canister are used up, the pressure differential will fall and the gap between the faces 38, 34 will increase so that the cross sectional area through which the fluid can flow to pass through the opening 26 also increases. Since the rate of flow of the fluid through the VPT is dependent 011 the pressure differential and the minimum cross sectional area through which 11 must pass, it can be arranged mat a decrease in the pressure differential is at least partially offset by an increase in the cross sectional area of the gap between the faces to maintain a generally constant flow rate.
The design of the flow control device 28 can he varied to suit the particular requirements of the application. The key is to create an interaction between the inner end wall 34, or in some cases the side wall, of the recess and the flow control element 30 that allows the propellant gas to pass through the VPT opening 26 in a controlled way. Hence, the seal between the flow control element 30 and the inner end wall 34 of the recess is partial and never complete in the pressure range required but increases in effectiveness with the pressure differential across the opening (which in turn is usually proportional to the pressure in the canister) in such a way that the rate of flow of the propellent through the VPT opening 26 remains generally constant within acceptable tolerances.
A further flow control device (not shown) can also be provided to control the flow of the liquid product through the valve 10. Since, the rate of flow of the gas through the VPT 26 is dependant on the pressure differential between the liquid inside the housing and the gas outside. By controlling the rate at which the liquid flows through the valve, the pressure 'differential can also be controlled which will affect the rate of flow of.the gas through the VPT. Controlling the flow rates of both the liquid and the gas allows greater control over fee rate at which the gas is bled through the VPT 26".
The further flow control device may be configured to maintain a substantially constant flow rate of the liquid product so that the ratio of propellant gas to liquid in the product dispensed also remain s substantially constant. Alternatively, the further flow control device may be configured to allow an increased flow of liquid product when the pressure in the canister is higher than when it is lower so that the ratio of gas propellant to liquid in the product dispensed increases as the pressure in the canister drops. The further flow control device may be provided at the inlet to the valve prior to the liquid mixing with the gas or at the outlet The further flow device may be of any suitable type and may, for example, be similar to the flow device 28 described above in relation to Figures 1A and 13 or any of the variations described below.
The rate at which the propellant gas is bled into the liquid as it is dispensed may alternatively be controlled by using a flow control means to control the rate of flow of the combined liquid and gas ether in th 3 valve itself, or downstream from the valve in the valve stem or the nozzle or between the valve and the stem or between the stem and the nozzle, for example.
The design of the flow control device 28 can be varied from that shown in Figs. 1A and 1B, in order to produce different flow effects and/or to adapt the device for use over different pressure ranges and/or for use with different

propellents and to cater for the desired flow range and the properties of the liquid product. In practice, it is expected that the configuration of the flow control device 28 will be adapted to meet the specific needs of the particular application, taking into consideration all the relevant factors including, for example, foe desired pressure range, the desired flow rate and the properties of the liquid product and the propellant gas.
Figures 2 to 22B are schematic drawings that illustrate a number of possible configurations that can be used in a flow control device 28 of a dispenser in accordance with the invention. These drawings show only the flow control device itself, or a part thereof. It will be appreciatec that the flow control devices shown will be incorporated into the valve 10 its itself in a manner similar to that shown in Pigs. 1A and1B.
As the flow control device 28 is adapted to deliver a fairly constant flow, across a range of pressures, it is necessary to be able to adapt the design to be able to deliver different flow rates across that range of pressures. Hence, if one configuration delivers a flow rate of 21/m for pressures of 2-10 bars, ft will be necessary to change the configuration in order to deliver a flow rate of say 31/m over the same pressure range. The simplest way to achieve this is to vary the size of the VPT opening 26 such that the larger the opening, the greater the flow rate. Alternatively, it is possible to provide multiple VPT openings 26 m the inner end wall 34 to provide a greater flow rate. Figures 2 end 3 illustrate flow control apparatus in which the size of the VPT opening 26 is varied whilst Figure 4 illustrates the use of multiple openings.
Other factors that may influence the flow rate are the surface finish of the inner end wall 34 of the recess 32 and/or the face 38 of the flow control element and the materials from which the inner end wall 34 and/oi: flow control element are manufactured. Thus, a smooth surface finish will tend to reduce the flow rate compared with a rough or textured surface finish. Also, as discussed

above, the use of harder materials will tend to increase the leakage between the flow control element 30 and the inner ead wall 34 and so will lead to a greater flow rate than would be achieved if softer materials are used.
Another way of controlling the flow rate through the devi ce 28 is to alter the overlap or contact area between the flow control element 3) and the inner end well 34 of the recess, The requited overlap to achieve a desired flow rate depends on the size of the opening or openings 26, the materials of the flow
*
control element 30 and the inner end wall 34, the surface finish of the corresponding surfaces of flow control element and the inner end wall 34, the pressure range involved and (he properties of the propellent gas. However, generally speaking, different overlaps permit different levels of leakage and these determine the flow rates. At higher pressures, over say 4 bar, the overlap can be reduced as the flow tends to be stable whereas at lower pressures the overlapping area may need to be larger. Figure 5 illustrates a flow control apparatus having a reduced overlap between the flow control element 30 and the inner end wall 34 compared wilh fast of the flow control apparatus shown in Figure 2.

Although not shown in the
accompanying drawings, s.a alternative
method of reducing the overlap, whilst ensuring the shuttle rem tins stable in the recess, is to reduce the outer diameter of shuttle and provide a number of vanes which project outwardly to contact the side wall of the recess. A further alternative, also not shown, would be to use a square or triangular shaped shuttle in which the corners of the shuttle contact the side wall of the recess.
A further design option as illustrated in Figure 6, is to provide a circular recess 40 in tixe face 38 of the flow cotxtrol element 30 that races t the inner end wall 34 of the recess. This reduces the contact area or overlap between the flow control element and the wall which, tends to increase the flow rate, p'urthermorne the recess 40 can be used as a swirl chamber to impart rotation into the

propellent gas causing it to form a spray or j'et as it passes through the opening 26. To aid this effect, the gas may be caused to spin around the recess in which the flow control element is located so mat when ft enters the recess 40 it is already spinning. This could be achieved by using a tangential input into the recess 32 from the outside of the valve 01 by using a known swirl device upstream from the flow control element Alternatively, or m addition, curved veins (not shown) could be put inside and around part of the cinular recess: 40 or VPT opening 26 to cause the propellant gas to spin and create a conical spray or jet into the liquid in the valve. If there is more than one VPT opening 26 in the wall, several recesses 40 could be provided, each acting as a swirl chamber for a respective one of the openings. The recess 40 can be of any writable shape.
Figure 7 illustrates a flow control device in which the recrss 32 and the flow control element 30 are conical or frusto-conioal, tapering inwardly towards the inner end wall 34, "With this arrangement, a spiral formation (not shown) can be applied to the side wall 42 of the recess or the side 44 of the flow control element 30 to cause the gas to spin and create a conical spray or jet through the VPT opening 26. In an alternative embodiment (net shown) the inner end wall 34 of the recess 32 may be omitted so that the fluid will pass between the conical side 44 of the flow control element 30 and the side wall 42 the recess 32. In such an embodiment, the side wall of tho element 30 and the side wall 42 of the passage comprise the corresponding faces between which me gas passes to reach the VPT opening. The flow control element 30 used in tins embodiment can "be of any suitable shape such as any of those shown ID the accompanying drawings. A swirl arrangement may also be used to cause the propellant gas to rotate either before it reaches the flow control element, after the flow control element or around the flow control element In certain applications, it may be advantageous for the partial seal between the flow control element and the conical side wall 42 of the recess to be formed along a
thin line. This could be achieved, for example, by not tapering the side 44 of the flow control element 30.
Figure 8 shows an arrangement in which a conical recess 46 is formed in the face 38 of the flow control element 30 and a corresponding conical recess 48 is formed in me inner end wall 34 of the recess about the VPT opening 26. This arrangement creates an expansion chamber 50 into which the propellent gas passes from between the flow control element 30 and the innar end wall 34 of the recess. Where tie wall 34 has multiple VPT openings 26, the face 38 of the flow control element and/or the wall 34 can have a corresponding number of recesses to provide an expansion chamber 50 for each opening. The openings 26 will usually be located centrally of their respective chambers. the expansion chambers) 50 can be of any suitable shape.
As shown.in Figuie.9, a post.52-may.project from-the flow control
v
element 30 into the VPT opening 26. Ef the gap between the post 52 and the side of the opening is small, the gas will form a spray or jet in th e liquid as; it passes through the gap. A series of fine grooves could be provided around the inside of the VPT opening 26 or on the surface of the post 52 that effectivesly create a number of semi-circular openings between the post and the wall defining the opening 26 which would operate as multiple fine spray/jet orifices into the interior of the valve housing 11. The post 52 could be flush with the VPT opening 26 and both the outer circumference of the post 52 and the opening 26 could be conical.
Whilst the face 38 of the flow control element 30 and me inner end wall 34 of the recess may be flat, they can be shaped in certain ways thai ensure only a partial seal is formed and to vary the flow rate. Figure 10 illustrates a flow control device 28 in which the face 38 of the flow control element 30 is convex but other shapes can be used. Varying the shape of the flow contro element 30
ana/or toe end wall 34 of the recess can be used to direct the gas into the valve housing in different ways.
Figure II illustrates -a flow control device in which the flow control element 30 is in the form of a flap connected to the walls of t the recess along one edge. As shown in Figure 11, the flap would normally adopt a position spaced from me end wall 34 of the recess fay a small amount when it is not subjected to pressure within the canister but is configured to be pressed into contact, or close proximity, with the wall by the pressure in the canister in use. However, the flap could be arranged to contact or lie close to the wall 34 at all times but be configured so that the effectiveness of the seal formed between the Hap and wall increases as the pressure of the fluid acting on the flap rises to control the rate of flow.
As discussed.above,, the surface-finish of the flow control element 30 and/or the wall 34 can be modified to vary the flow rate and other flow characteristics. For example, a scries of fine rods could project from the wall 34 or from the face 38 of the Sow control element 30 to easure a nrinfinum spacing is maintained and which could act as a filter. Alternatively, grooves
could be fonned in the wall 34 and/or in the face 38 of the flow control element. The grooves would ensure that mere was at least a minimum flow of gas and could be arranged to impart particular flow characteristics cs to the gas causing it to spry into the liquid through the VPT opening 26.
Figures 12 to 14 illustrate some examples of groove arrangements that might be used These drawings show the face 3 8 of the flow control element 30 with the inner circle 54 being indicative of the position of the VPT opening 26 in the inner end wall 34 of the recess. It should be understood that; the grooves could be formed in the wall 34 of the recess rather than, in the end face 3 8 of the . flow control element 30 or in both if desired,
In Figure 12, a circular groove 56 having a diameter larger than that of the VPT opening 26 has a number of radial spoke like grocves 58 leading towards the centre of the flow control element 30 and the VPT opening 26. With this arrangement, the gas would collect in the circular groove 56 and then travel along the radial grooves 58 towards their inner ends when} it would enter the VPT opening 26 as a series of fine sprays or jets. If the end. face 38 of the flow control element and the wall 34 are conical, the gas would spray or jet outwards into the valve housing and could be directed so that the various sprays/jets hit each other or miss each other as required.
In Figure 13, an outer circular groove 56 is connected to a central recess 60 by two straight radial grooves 62, 64 which may be of different sizes. The radial grooves 62, 64 are arranged to enter the central recess non-tangenti-ally on different sides of the VPT opening 26 so as to cause the gas to rotate within the central recess 60 so that it is spinning as it enters the VPT ope fling 26.
In Figure 14, an outer circular groove 56 is connected to a central recess 60 by two curved radial grooves 66, 68 which direct the gas into the central recess tangentially in lie manner of a swirl chamber to case the gas to spin in the recess from which it passes through the VPT opening 26.
Any suitable groove pattern can be applied to the surfac e of the flow control element 30 and/or the wall 34. Where the grooves are formed in the wall, the flow control element 30 would normally cover all the g rooves so that the fluid had to pass between the element 30 and the wall 34 to reach the grooves.
The embodiment shown in Figures 15A and 15B illusurate how the control element 30 can be modified to form an integral spring 10 form a self cleaning VPT. A main body portion 70 of the control element has a dish shape with a concave face 38 which opposes the inner face of the wall 34 with -the opening 26. As shown in Figure 15B, the main body portion can be compressed
against the wall 34 by the pressure of the gas flowing through the recess 32 so as to act as a flow control device in me manner previously described When the valve 10 is closed and the flow of gas through the VPT 26 stops the main body portion 70 will resume its dished shape, as shown in Figure 15A, so that any foreign matter trapped between the flow control element 30 and the wall 34 is released. The flow control element 30 may have ft central post 52 which projects into the opening 26 as shown or this may be omitted. The flow control element 30, or at least part of the dish shaped main body portion 70 may be made of a flexible, resilient material so that me spring effect is retained for longer man would be the case with a generally rigid material.
la the embodiment shown in Figures 16A and 16B, tho flow control element 30 has a central post 52 which extends into the VPT opening 26 in the wall 34 but is also provided with a swirl inducing formation 72 on the face 38 of the element which abuts the wall 34. As shown in Figure 16B, which is an end elevation of the element 30, the swirl foxmation 72 include two curved grooves which direct the gas into a circular recess 74 surrounding the post 52 so that the gas spins about the post forming a cone as it passes through the VPT 26. The height of the post 52 in the opening 26 dictates the shape of the come. Unlike a conventional swirl arrangement, the control element 30 is able to move relative to the wall 34 to control the rate of flow of fluid through me VPT opening 26. Causing the gas to swirl prior to entering the valve housing can help to promote mixing of the gas and the liquid in the housing, which in ten helps to improve the quality of the final spray produced at the nozzle outlet
It should be appreciated that any of the various features shown in the embodiments described herein can be combiried in any suitable way to produce a desired flow control arrangement For example, Figures 17A and 17B illustrate an embodiment which combines the features of the dished control element 30 as described above in relation to Figures 15A and 15B and the swirl

inducing grooves 72, similar to that described above in relation to Figures 16A and 16B, formed on the face 38 of the element which abuts the wall 42.
The face 38 of the element 30 need not be flat, Figures 18,19,20A and 20B illustrate embodiments in which the control element 30 hat. a tapered face 38 for cooperation with the end wall 34 of the recess. In the embodiment shown in Figure 18, the end wall 34 of the recess 32 is flat so that the tapered wall 38 of the control element makes a partial point or line seal with tfo wall 34 a.r, the edge of the opening 26. In the Figure 19 embodiment, the wall 34 has a corresponding tapered wall surface 76 about the opening 26 which mates with the tapered face 38 of the flow control element Figures 20A and 20B illustrate an embodiment similar to that of Figure 19 except that a swirl arrangement 72, similar to that described above in relation to Figures 16A and 16B, is formed on fee tapered surface 38 of the flow control element The swirl inducing grooves 72 can best be seen in Figure 20B, which is an end elevation from above of the flow control element 30.
Figures 21A and 21B illustrate an embodiment in which this flow control element has grooves 78 formed in the surface 38 which contacts the wall 34. Figure 21B is an end elevation of the flow control element 30 which has a central recess 80 surrounded by an annular portion 82 which abuts the wall 34. The grooves 78 extend across the annular portion on two sides so that the fluid can pass through the grooves into the central recess and pass out though the VPT opening 26. The control element 30 also has a post 52 which projects from the centre of me recess into the opening 26 in the wall 34 but this could be omitted. The control element 30 may be made of a flexible material so that when the element 30 is pressed into contact with the wall, the grooves 78 are partially collapsed to resist the flow. The greater the force acting to push the element 30 into contact with the wall 34, the more the grooves are collapsed and greater the resistance to the flow of gas. The arrangement can be used to control the flow rate of gas through the opening 26 since the minimum cross
sectional area of the grooves through which the gas flows is varied as a function of the force biasing the element in to the end wall 34, which is itself a function of the pressure differential acting across the opening 26. In an alternative arrangement, the grooves could be formed on the inner face of the wall 34 so that the flexible material of the flow control elemem is pushed into the grooves when the element is compressed against the end wal 1 34 to partially fill the grooves and so regulate the flow through the opening. The central recess could be reduced in size or omitted altogether so that the grooves 78 are formed in a flat face 38 of the flow control element so long as they are in fluid connection with the opening 26 when in use.
The recess 32 hi which the flow control element 30 is located can be of any suitable shape and especially could be any of the shapes ol the chambers disclosed in the applicant's co-pending International patent application published as WO, 2005/005055, the entire content of which, is hereby incorporated by reference. Thus me shape of any of the recesses in any of the embodiments described above can be modified in accordance with the principles discussed in WO 2005/005055. Similarly, where a recess 40 or expansion chamber 50 is provided between the flow control element 30 and the wall 34, the recess or chamber can also be of any suitable shape including those disclosed in WO 2005/005055.
A number of fine VPTs enable a better mixing of the gas in the liquor and ultimately a finer spray is produce but such fine holes are difficult to produce. However, where the VPT 24 includes a flow control devi ce 28 such as those described herein the VPT hole or opening 26 can be much larger than with a conventional VPT making it easier to manufacture.
It is also possible to design the flow control device 28 to allow only a gas to pass through whilst preventing, or at least minimising, the passage of a fluid through the device. This can be achieved by configuring the apparatus so

that the flow control element 30 .creates a close partial seal with the will 34 through which only a gas can pass. In this arrangement, the flow control element 30 and/or the wall 34 may be made of or covered by, a flexible material like rubber that forms good seal. In this arrangement, the wall 34 against which the flow control element 30 abuts may be in the form of a fine mesh that could become the equivalent of a membrane.
As can be seen from some of the embodiments described above, in.
addition to controlling the rate of flow of the gas, the flow control device 28

can be designed to cause the gas to spin and/or jet into the bousing. This is advantageous as it generates increased turbulence inside the housing, which helps to promote mixing between the gas and liquid and improves the final spray quality.
A further advantage of the various embodiments described herein is that the flow control device 28 is self cleaning. The element 30 can be moved away from the end wall 34 and the opening 26 when the valve is dosed and the pressure inside and outside the housing is equalised. This enables any small particles trapped between the element 30 and the end wall to fill clear of the VPT to prevent clogging. The ability to make the openings 26 in the present embodiments larger than standard VPT openings use of larger VPT holes can also be utilized when filling the canisters with gas as me gas can be injected under pressure through the valve 11 and the VPT opening 26, moving the flow control element 30 away from the end wall 34.
In a further variation, the outer end of the flow control element 30 which faces away from the end wall 34 of the recess can be adapted to Ibnn a filter to prevent debris from entering the valve 11 through the VPT opeiung 26, Thus the outer end could have a conical or fan like section with a number of fine slits or holes through which the gas can pass but which are small enough to trap

most foreign particles. The conical or fan like section may extend outwardly into contact with the side wall of the recess 32.
The flow control element 30 may be manufactured from a combination of materials to provide the required properties. For example, the element may be manufactured from two or more different materials using a bi-injection moulding technique. Hence, the flow control element could be mamufactured to comprise a rigid core with a flexible outer-portion for contacting the wall to
•
form a seal. Furthermore, two or more flow control elements could be used in series in the same recess so that they push agaiust each other or with one going inside a recess or opening formed in or through soother element 3 ).
It will be appreciated that the invention is not necessarily limited to dispensers comprising a flow control device 28 of the types described in lie present application but can be implemented using any suitable flow control device to control the flow rate at which the propellant is introduced into the liquid as it is dispensed. It should also be apereciated that the flow control
device need not be provided in a side wall of the mousing but c ould be provided anywhere in the housing such as in a base region surrounding the inlet Indeed the flow control device can be provided anywhere within the valve; including in the valve stem or on an auxiliary part to the valve. For example, if the dispenser is fitted with a tilt device mounted to or integrated with the dip tube to enable the dispenser to function more effectively wher it. is tilted or inverted, the flow control device may be provided in the tit device. For a more detailed description of various embodiments of tilt device, the reader should refec to tile applicant's international patent application WO 2004/022451, the content of which is hereby incorporated in its entirety by reference.
In addition, the invention is not limited to use with dispensers having the type of valve 10 described herein but can be applied to aerosol dispensers having any suitable form of valve. For example, the valve could be of the

female type or of the split valve type in which the propellant gas and the liquid remain separated ha tile valve and mix either in the nozzle or in lie valve stem. In this latter case, the flow control device could "be located in the stem, between the stem and the nozzle, or in the nozzle itself the invention can also be applied to aerosol dispensers in which the propellant is separated from the liquid product in the canister by a flexible bag. For example in certain dispensers the liquid product is contained in an elasticised or stretchable bag which expands -when it is filled to compress air between itself and the outer walk of the canister. When the dispenser valve is opened, the compressed air acts as a propellant, squeezing the bag and forcing the contents through the valve under pressure.
Whereas the invention has been described in relation to what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed arrangements but

rather is intended to cover various modifications and equivalent constructions included within the spirit and scope of the invention. It should bo noted that a valve for an aerosol dispenser comprising a VPT and a flow control means for controlling the rate of flow of a propellant gas through the VPT may also be claimed.
Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers,.steps or components referred to, bat not to preclude the presence or addition of one. or more other feasure, integer, step, component or group thereof.

Claims
1. An aerosol dispenser comprising a canister adapted to contain a liquid product to be dispensed and a propellant present in the canister at least partly as a gas, said dispenser having a valve for controlling the release of the liquid product from the canister and means for introducing a portion of the gaseous propellant into the liquid product as it is dispensed, the dispenser further comprising a flow control means for varying the rate at which the propellant gas is introduced into the liquid product, in dependence on the pressure of the contents in the canister, characterised in that the flow control means is configured such that the ratio of propel] ant gas to liquid product dispensed is increased as the pressure in the dispenser decreases over the useful life of the dispenser.
2. An aerosol dispenser as claimed in claim 1, in which the flow
control means is configured to maintain the rate of flow of the
gaseous propellant into the liquid as it is dispensed generally
constant over the useful life of the dispenser.
3. An aerosol dispenser as claimed in claim 1, in which the flow
control means is configured such that the rate of flow of the gaseous
propellant into the liquid as it is dispensed increases as the pressure
in the canister decreases over the useful life of the canister.
4. An aerosol dispenser as claimed in any one of claims 1 to 3, in
which the flow control means is configured to reduce the rate of
flow of the propellant gas into the liquid product when the dispenser
is substantially full when compared with the rate of flow of an
equivalent conventional dispenser having no such flow control
means.

5. An aerosol dispenser as claimed in any one of claims 1 to 4, in
which the flow control means is provided in the valve.
6. An aerosol dispenser as claimed in any one of claims 1 to 5, in
which the flow control means is provided hi the flow path of the gas
upstream of the point at which the propellant gas mixes with the
liquid product.
7. An aerosol dispenser as claimed in claim 6, in which the dispenser
further comprises an outlet nozzle mounted to the valve by means of
a valve stem, in which the flow control means is provided in the
nozzle, or in the valve stem, or between the valve and the stem, or
between the stem and the nozzle, or in an auxiliary device mounted
to or associated with the valve.
8. An aerosol dispenser as claimed in claim 6, in which the propellant
gas is introduced into the liquid product within a housing of the
valve, such that the combined propellant gas and liqi lid product flow
through the valve along a common flow path.
9. An aerosol dispenser as claimed in 7, in which the valve is a spilt
type valve in which the propellant gas and the liquid product flow
through the valve along separate flow paths, with the gas and liquid
flow paths combining downstream of the valve, in which the flow
control means is provided at any suitable position in the flow path of
the gas prior to the gas mixing with the liquid produc t.
10. An aerosol dispenser as claimed in any one of claims 6 to 9, in
which the flow control means further comprises means for
controlling the rate of flow of the liquid product as it is dispensed,
the further flow control means being provided in the flow path of the
liquid product upstream of the point at which the liquid mixes with
the propellant gas.

11. An aerosol dispenser as claimed in claim 10, in which the further
flow control means is configured to reduce the ra :e of flow of the
liquid through the valve as the pressure of the contents in the
canister falls.
12. An aerosol dispenser as claimed in any one of the previous claims, in
which the flow control means comprises a body having an opening
through which the fluid to be controlled flows, and a flow control
element upstream of the opening, in which, in use when fluid is
flowing through the opening, the pressure of the fluid acting on the
flow control element pushes the element towards the opening to
restrict the flow of the fluid through the opening.
13. An aerosol dispenser as claimed in claim 12, in whi ;h the resistance
to the flow of fluid through the opening provided I y the element is
proportional to the pressure differential across the opening.
14. An aerosol dispenser as claimed in claim 12 or claim 13, in which
the flow control means is configured such that, in use, the fluid is
constrained to flow between the flow control element and a surface
of the body in order to reach the opening.
15. An aerosol dispenser as claimed in claim 14, in which the flow
control element is configured such that in use, a face on the flow
control element is brought into contact, or close proximity with, a
corresponding face of the body when the element is pushed towards
the opening and the fluid is constrained to pass between the
corresponding faces to reach the opening.
16. An aerosol dispenser as claimed in claim 15, in which the minimum
cross sectional area between the corresponding faces through which
the fluid must flow to reach the opening varies in dependence on the
pressure differential across the opening.

17. An aerosol dispenser as claimed in claim 16, in which the minimum
cross sectional area between the corresponding facss through which
the fluid must flow to reach the opening is proportional to the
pressure differential across the opening.
18. An aerosol dispenser as claimed in any one of claims 12 to 17, in
which the body defines a recess or chamber and the at least one
opening is formed in a downstream end of the chamber.
19. An aerosol dispenser as claimed in claim 18, in which the flow
control element comprises a shuttle member located in the recess or
chamber.
20. An aerosol dispenser as claimed in claim 19, in which the Jihuttle
member is in the form of a disc.
21. An aerosol dispenser as claimed in any one of claims 12 to 20, in
which the body comprises a housing of the valve and the opening is
configured such that propellant gas in the canister above the liquid
product can pass through the opening to mix with the liquid product
inside the valve housing, the flow control element acting to control
the rate of flow of the propellant gas through the at least one
opening.
22. An aerosol dispenser as claimed in any one of the previous claims, in
which the liquid product is contained within a flexible bag inside the
container.
23. An aerosol dispenser as claimed in any one of the previous claims, in
which the flow control means is self-cleaning.
24. An aerosol dispenser as claimed in any one of the previous claims, in
which the flow control means also functions as a filter.

25. An aerosol dispenser as claimed in any one of the previous claims: in
which the dispenser further comprises an azomising nozzle
configured such that the product is dispensed thicugh an outlet of
the nozzle in the form of an atomised spray or aerosol.
26. An aerosol dispenser as claimed in any one of the pr evious claims, in
which the propellant gas is present in the canister mainly or
exclusively as a compressed gas. l
27. An aerosol dispenser as claimed in claim 26, in whioh the propellant
gas is compressed air or compressed nitrogen or compressed carbon
dioxide.
28. An aerosol dispenser comprising a canister adapted to contain a
liquid product to be dispensed and a propellant present in the
canister at least partly as a gas, said dispenser having a valve for
controlling the release of the liquid product from lie canister and
means for introducing a portion of the gaseous propellant into the
liquid product as it is dispensed, characterised in that the dispenser
further comprises a first flow control device for va rying the rate at
which the propellant gas is introduced into the liquid product in
dependence on the pressure of the consents in the canister and a
second, separate flow control means for varying the rate at which the
liquid flows through the valve in dependence on thepressure of the
contents in the canister, the first and second flow control devices
being configured such that the ratio of propellent gas to liquid
product dispensed is increased as the pressure in the dispenser
decreases over the useful life of the dispenser.
29. An aerosol dispenser as claimed in claim 28, in which the propellant
gas is introduced into the liquid product within a housing of the

valve, such that the combined propellant gas and liquid product flow through the valve along a common flow path.
30. An aerosol dispenser as claimed in claim 28 or clam 29, in which
the second flow control device is configured to reduce the rate of
flow of the liquid through the valve as the pressure in the canister
drops.
31. An aerosol dispenser as claimed in any one of claims 28 to 30, in
which the propellant is present mainly or exclusively as a
compressed gas.
32. An aerosol dispenser as claimed hi claim 31, in whi ch the propellant
is compressed air or compressed nitrogen or compressed carbon
dioxide.
33. An aerosol dispenser comprising a canister adapted to contain a
liquid product to be dispensed and a propellant present in the
canister at least partly as a gas, said dispenser having a valve for
controlling the release of the liquid product from the canister and
means for introducing a portion of the propellant gss into the liquid
product as it is dispensed, the dispenser being configured so that the
portion of the propellant gas is introduced into the liquid product
within the Valve so that the combined liquid and propellant gas flow
through the valve along a common flow path, characterised in that
the dispenser further comprises a flow control mean;; for varying the
rate at which the propellant gas is introduced into the liquid product
in dependence on the pressure of the contents in the canister, the
flow control means being configured such that the rado of propellant
gas to liquid product dispensed is increased as the pressure in the
dispenser decreases over the useful life of the dispenser.

34. An aerosol dispenser as claimed in claim 33, in which the flow
control means comprises a first flow control device for varying the
rate at which the propellant gas is introduced into the liquid product
in dependence on the pressure of the contents in the canister, the first
flow control device being located in the flow path of the gas
upstream of the point at which the propellant gas is introduced into
the liquid product.
35. An aerosol dispenser as claimed in claim 34, in which the flow
control means further comprises a second, separate flow control
device for varying the rate at which the liquid flows through the
valve.
36. An aerosol dispenser as claimed in claim 35, in which the second
flow control device is configured to reduce the rate of flow of liquid
through the valve as the pressure in the canister drop s.
37. An aerosol dispenser as claimed in claim 35 or clam 36, in -which
the second flow device is located in the flow pat h of the liquid
upstream of the point at which the propellant gas is introduced into
the liquid product.
38. An aerosol dispenser as claimed in any one of claims 33 to 37, in
which the valve comprises a valve housing and a movable valve
member at least partially located in the housing for controlling the
flow of liquid through the valve, the dispenser being configured such
that the propellant gas is mixed with the liquid product within the
valve housing.
39. An aerosol dispenser as claimed in any one of claims 33 to 38, in
which the propellant gas is present in the canister mainly or
exclusively as a compressed gas.
40. An aerosol dispenser as claimed in claim 39, in whi.ch the propellant gas is compressed air or compressed nitrogen or compressed carbon dioxide.