Abstract:
A valve assembly including a housing with an internally projecting lip that seals against an outer surface of a valve stem inserted through it. A gas inlet is provided above the lip and a liquid inlet is provided below the lip. The lip thus ensures that a gas flow path and a liquid flow path are kept separate until the valve stem is moved to an open position, at which point a liquid inlet hole in the stem is brought into communication with the liquid inlet in the housing and a gas inlet hole in the stem is brought into communication with the gas inlet in the housing for the fluids mix in an outlet conduit in the stem. The arrangement means that there is no contact between the liquid and a sealing gasket, thereby avoiding swelling of the gasket that can cause the stem to stick.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a valve assembly, in particular a valve assembly for use in an aerosol spray device for discharging a liquid product (e.g. a household product such as an air freshener) in the form of a spray. The invention has particular application to aerosol spray devices which utilise a compressed gas propellant rather than a liquefied gas propellant. 
       BACKGROUND TO INVENTION 
       [0002]    Broadly speaking, aerosol spray devices comprise a container holding a liquid to be discharged together and an outlet nozzle associated with a valving arrangement which is selectively operable to allow discharge of the liquid as a spray from the nozzle by means of the propellant provided within the container. 
         [0003]    Both “compressed gas propellant aerosols” and “liquefied gas propellant aerosols” are known. The former incorporate a propellant which is a gas at 25° C. and at a pressure of at least 50 bar (e.g. air, nitrogen or carbon dioxide). Such a gas does not liquefy in the aerosol spray device. On opening of the valving arrangement, the compressed gas “pushes” liquid in the spray device through the aforementioned nozzle that provides for atomisation. There are, in fact, two types of “compressed gas propellant aerosols”. In one type, only liquid from the container (“pushed-out” by the compressed gas) is supplied to the outlet nozzle. In the other principal type, a portion of the propellant gas from the container is bled into the liquid being supplied to the nozzle which atomises the resulting two-phase, bubble-laden (“bubbly”) flow to produce the spray. This latter format can produce finer sprays than the former. 
         [0004]    In contrast, “liquefied gas propellant aerosols” use a propellant which is present (in the aerosol spray device) both in the gaseous and liquid phases and is miscible with the latter. The propellant may, for example, be butane, propane or a mixture thereof. On discharge, the gas phase propellant “propels” the liquid in container (including dissolved, liquid phase propellant through the nozzle). 
         [0005]    It is well known that “liquefied gas propellant aerosols” are capable of producing finer sprays than “compressed gas propellant aerosols”. This is due to the fact that, in the former, a large proportion of the liquefied gas “flash vaporises” during discharge of liquid from the aerosol spray device and this rapid expansion gives rise to a fine spray. Such fine sprays cannot generally be achieved with “compressed gas propellant aerosols”, in either of the two principal formats described above. 
         [0006]    Attempts have been made to improve the “fineness” of sprays generated by “compressed gas propellant aerosols”. Prior art proposals have included the possibility of “bleeding off” some of the compressed gas (e.g. nitrogen) that is present in the container and mixing this with the liquid product to achieve “two fluid atomisation” which is a technique known to provide fine sprays for other areas of spray technology, e.g. liquid fuel combustion. However it has been found extremely difficult to produce fine sprays using two fluid atomisation with aerosol spray devices, and the nearest approach has been to use the equivalent of a vapour phase tap (VPTs are used in “liquefied gas propellant aerosols”) to bleed some gas into the valve. However results for improving spray fineness have not been significantly beneficial. 
         [0007]    PCT Patent Applications (Publication) Nos. WO 2011/061531 and WO 2011/128607, the contents of which are hereby incorporated by reference, each disclose aerosol spray devices for producing fine sprays in the case of “compressed gas propellant aerosols” (although there is some applicability also to “liquefied gas propellant aerosols”). Devices disclosed in WO 2011/061531 and WO 2011/128607 incorporate a spray discharge assembly incorporating a flow conduit for supplying fluid from a container to a spray outlet region of the device. The flow conduit has at least one first inlet for liquid from the container and at least one second inlet for propellant gas from a head space of the container. The spray discharge assembly further incorporates a valving arrangement such that movement of a valve stem from a first to second limit position opens the first and second inlets to cause a bubble laden flow to be generated in the flow conduit for supply to the spray outlet region. An aerosol device of this general type is illustrated in  FIG. 1 , which illustrates a known aerosol spray device  1  in the normal “rest” or “closed” position. 
         [0008]    The device  1  comprises a pressurised container  2  on the top of which is mounted an spray discharge assembly  3  which, as schematically illustrated in the Figure, is crimped on to the top portion of container  2 . Provided within container  2  is a liquid  5  to be dispensed from the device by a pressurised gas such as nitrogen, air or carbon dioxide, which has limited solubility in the liquid  5  and is in a head space  6  of the container  2 . The gas in the head space  6  may, for example, be at an initial pressure of 9 to 20 bar depending upon the type of container in use. The initial pressure may, for example, be 9 or 12 bar. There are however higher pressure “standard” cans now available (but as yet little used), for which the initial pressure is for example 18 bar or higher. Such cans can also be used in the present invention. Higher initial can pressure is good because there is more mass of gas available to help atomisation and higher nozzle velocities which also helps atomisation and also the proportionate loss in can pressure as the can empties is less. This helps maintain spray quality and flow rate better during can lifetime. 
         [0009]    The valve assembly  3  comprises a generally cylindrical, axially movable valve stem  7  having an axial bore  8  extending from the upper end of valve stem  7  part way towards the lower end thereof. At its lower (proximal) end, valve stem  7  locates within a cylindrical housing  9  positioned internally of the container  2  and at its upper (distal) end is fitted with an actuator in the form of a cap  10  having a spray outlet region  11 . Provided at the outlet end of region  11  is a conventional MBU (Mechanical Break-Up Unit) insert  13 . The valve assembly  3  is secured to the top of the container  2  by means of a metallic top cap  30  which is crimped at a central portion to the upper end of the valve housing  9  and crimped at an outer periphery to the upper rim  2   a  of the container. An outer gasket (not shown) would typically be secured in place between the upper rim  2   a  and the outer periphery of the top cap  30  to ensure a hermetic seal. 
         [0010]    In broad outline, the aerosol spray device  1  is operated by pressing down on the cap  10  to cause downward movement of valve stem  7  to an “open” position with resultant discharge of a spray from spray outlet region  11 . As shown in the drawings, valve stem  7  is biased upwardly of the container  2  by means of a coil spring  14 . Lower end of coil spring  14  locates around an aperture  16  in lower wall  17  of the housing  9 . Depending from wall  17  is a tubular spigot  18  having a lower enlarged end  19  to which is fitted a dip tube  20  which extends to the base of the container  2 . It will be appreciated from the drawing that the lower region of container  2  is in communication with the interior of the housing  9  via the dip tube  20 , spigot  18  and aperture  16  (which provides a liquid inlet for housing  9 ). 
         [0011]    In certain embodiments disclosed in WO 2011/061531 and WO 2011/128607, such as that illustrated in accompanying  FIG. 1 , the valve assembly includes a pair of sealing gaskets: a first  23  dedicated to sealing liquid inlets  28  to the stem; and a second  21  dedicated to sealing gas inlets  29  to the stem. The annular gaskets  22  and  23  are formed of rubber or other elastomeric material and are dimensioned to seal against the outer surface of valve stem  7 . Formed in the wall of the housing  9  between the two gaskets  22  and  23  are a plurality of ports  24  which provide for communication between the pressurised gas in the head space  6  and an annular clearance  21   a.    
         [0012]    The liquid feed passageways  28  and gas bleed inlet passageways  29  are axially spaced from each other by a distance such that, in the “rest” condition (“closed” position) of the aerosol as shown in  FIG. 1 , the passageways  29  are sealed by upper gasket  22  and passageways  28  are sealed by lower gasket  23 . The cross-sections of the passageways  28  and  29  together with the axial spacing between these passageways and the dimensions of the upper and lower gaskets  22  and  23  are such that on depression of the valve stem  7  to the open position the gas bleed inlet passageways  29  are opened simultaneously with (or more preferably just before) the liquid feed passageways  28 , thereby causing the generation of bubble laden flow in the outlet conduit  8  for supply to the spray outlet region  11  for discharge therefrom in the form of a fine aerosol. 
         [0013]    In certain other embodiments disclosed in WO 2011/061531 and WO 2011/128607, such as illustrated in accompanying  FIG. 2 , a single gasket  23  is used to seal both the liquid inlet  72  to the stem and the gas inlet  71  to the stem. On movement of the valve stem  7  from the closed position to the open position, the stem inlets  71 ,  72  are moved proximally of the gasket  23  and are therefore brought into fluid communication with, respectively, a gas inlet  73  in the housing  9 , and a liquid inlet  16  in the housing, thereby causing the generation of bubble laden flow in the outlet conduit  8 . Further examples of single gasket embodiments are shown and described by reference to  FIGS. 9 a    to  16  of WO 2011/128607, one example of which is shown in the accompanying  FIGS. 3 a  to 3 c   , in which the single gasket  23  is in fact formed in two adjacent parts: a thin gasket  112  and an annular seal  111 , supported in the housing by a support ring  110 . 
         [0014]    The thin gasket  112  is shown in greater detail in  FIG. 3 c    and comprises a disc having a central aperture  113  that is sized to be a close fit about the valve stem  7 . A radial groove  123   a  extends in one side of the disc from the central aperture to an edge of the disc, where the groove connects with an axial notch  123   b  that extends through the edge of the disc. The groove  123   a  and notch  123   b  together comprise a gas inlet port that forms a gas flow path from the headspace  6  to the gas bleed inlet  121  when the valve stem is depressed, as in  FIG. 3 b   . A notch  124  extends through the disc  112  at a point at the edge of the aperture  113  diametrically opposite to the groove  123   a.  When the valve stem is depressed, the notch  124  forms a liquid flow path between the annular clearance  21  and the liquid feed inlet  122 . The annular clearance  21  is in fluid communication with the liquid inlet  16  in the housing via an axial channel  106  through the lower portion of the valve stem  7  and a transverse opening  108  located at the upper end of the channel  106 . 
         [0015]      FIG. 3 a    shows the valve stem  7  of this exemplary known single gasket valve assembly in a closed position, in which the valve stem  7  is extended out of the housing  9 , under the action of the spring  14 , so that the gas bleed inlet(s)  121  and the liquid inlets(s)  122  are each on the opposite (distal) side of the seal  23  to the gasket  112 , or are at least blocked by the seal. 
         [0016]    An advantage of a single gasket arrangement is that it employs fewer parts and thus reduces material, manufacturing and assembly costs in comparison to double gasket arrangements. Additionally, it may readily be produced in dimensions well suited to manufacture with the same overall dimensions as conventional liquefied gas propellant aerosol valves. However, in such known single gasket arrangements, there is a risk that the gasket may swell from contact with the liquid contents  5  of the spray device, at least for certain liquids. Such swelling would increase the friction between the gasket  23  and the valve stem  7 , which could lead to the valve stem becoming stiffer to move or even becoming stuck. Also, in order to ensure that the stem gas and liquid inlets are brought into fluid communication with their associated housing gas and liquid inlets on movement of the stem  7  to the open position, it has been necessary to include features, such as the stem lugs  7   a  and associated housing grooves  9   a  of  FIG. 3 b   , to prevent rotation of the valve stem  7  in the housing  9 , and to account for proper orientation of the valve stem during assembly. 
         [0017]    It is therefore an object of the invention to provide a single gasket valve arrangement in which the liquid contents of the spray device are kept out of contact with the gasket. It is a further object of the invention to provide a single gasket valve arrangement in which the valve stem can be rotated to any position and still function. 
       SUMMARY OF THE INVENTION 
       [0018]    According to a first aspect of the present invention there is provided a valve assembly for an aerosol spray device, the assembly comprising:
       a housing with internal walls defining a valve chamber, the chamber having a liquid inlet for fluid communication with liquid in the aerosol spray device, and a gas inlet for fluid communication with gas in the aerosol spray device; and   a valve stem having proximal and distal ends, the proximal end received in the valve chamber and the distal end projecting through a sealed opening in the valve chamber, the valve stem including an outlet flow conduit with an outlet aperture at the distal end and, more proximally, at least one first stem inlet for liquid and at least one second stem inlet for gas;   wherein the housing includes a lip projecting inwardly from the internal walls to form a seal around a perimeter of the valve stem along at least a portion of the valve stem, wherein the valve chamber liquid inlet is proximal of the lip and the valve chamber gas inlet is distal of the lip;   wherein the valve stem is moveable between:
           a closed position in which the at least one first stem inlet is distal of the lip and the at least one second stem inlet is distal of the sealed opening in the valve chamber, such that the at least one first stem inlet is not in fluid communication with the valve chamber liquid inlet and such that the at least one second stem inlet is not in fluid communication with the valve chamber gas inlet; and   an open position in which the at least one first stem inlet is proximal of the lip so as to be in fluid communication with the valve chamber liquid inlet, and the at least one second stem inlet is proximal of the sealed opening in the valve chamber and at least partially distal of the lip so as to be in fluid communication with the valve chamber gas inlet, whereby a bubble laden flow is created in the flow conduit.   
               
 
         [0025]    The arrangement means that the liquid flow path is kept separate from the gas flow path (until the valve is in the open position, when the liquid and gas mix in the outlet flow conduit) by virtue of the sealing interface between the lip and the valve stem, rather than by a sealing gasket. The liquid thus never comes into contact with the gasket, and accordingly swelling of the gasket due to such contact is avoided. 
         [0026]    Another advantage of the arrangement is that there is no need to align the stem in the housing; the valve will operate with the stem at any rotational orientation within the housing, in contrast to prior art arrangements in which it has been necessary to align the constituent parts of the flow paths in the stem with corresponding constituent parts in the valve housing. This makes manufacture easier, and provides for a more versatile valve. 
         [0027]    The number of components is also reduced in comparison to comparable prior art valve assemblies, which thus reduces the complexity and cost of the valve and its manufacture. 
         [0028]    The at least one second stem inlet for gas is preferably downstream of said at least one first stem inlet for liquid. 
         [0029]    The valve stem is typically biased towards the closed position. 
         [0030]    The valve assembly may further comprise a limit stop to prevent movement of the valve stem distally beyond the closed position. The limit stop may comprise a shoulder projecting radially from the valve stem towards the proximal end thereof for abutment against said lip. The shoulder may include a channel which, when the valve stem is in the open position, allows fluid to flow from the valve chamber liquid inlet to the at least one first stem inlet, but which when the valve stem is in the closed position is closed off by the abutment against the lip, preventing the flow of liquid through the channel. The channel may comprise at least one radially extending conduit in fluid communication at one end thereof, in the centre of the valve stem, with a bore from the distal end of the valve stem, and at the other end thereof with a groove in the outer surface of the shoulder running parallel to the bore and to the outlet conduit. 
         [0031]    At least the portion of the valve stem about which the lip forms a seal preferably has a constant cross-section. Typically, the valve stem has a circular cross-section. 
         [0032]    The housing may comprise a cup portion and a cap portion. The valve chamber liquid inlet may be formed through the cup portion, and the valve chamber gas inlet may be formed through the cap portion. 
         [0033]    The valve chamber gas inlet may comprise a plurality of radial grooves defined between corresponding radial ribs on an upper surface of the housing, in conjunction with a conduit through the housing to the outer surface thereof, for communication with the headspace of a container to which the spray device is fitted. 
         [0034]    The sealed opening is typically sealed by a gasket, which is preferably a planar, annular gasket. Where the valve chamber gas inlet comprises a plurality of radial grooves defined between corresponding radial ribs on an upper surface of the housing, the gasket preferably also defines an upper bound of the radial grooves in the housing. 
         [0035]    In certain prior art arrangements, it has been necessary to provide a separate part to support the gasket within the housing, such as the support ring  110  of  FIGS. 3 a  and 3 b   . That is not necessary with the inventive arrangement, in which the upper surface of the housing has a dual purpose of supporting the gasket and defining (part of) the gas flow path. 
         [0036]    The aerosol spray device is preferably of the type comprising a pressurised or pressurisable container holding a liquid to be discharged from the device by a propellant that is a gas at a temperature of 25° C. and a pressure of at least 50 bar. This corresponds to “compressed gas propellant aerosols”, such as nitrogen or carbon dioxide, which do not have the well-known disadvantages associated with liquefied gas propellant aerosols, such as butane or propane. 
         [0037]    According to a second aspect of the invention, there is provided an aerosol spray device comprising a pressurised or pressurisable container holding a liquid to be discharged from the device by a gaseous propellant that is a gas at a temperature of 25° C. and a pressure of at least 50 bar and a spray discharge assembly mounted on the container, said spray discharge assembly incorporating:
       the valve assembly according to the first aspect of the invention; and   a spray outlet region having an outlet orifice from which fluid from the container is discharged.       
 
         [0040]    The aerosol spray device may further comprise an actuator assembly which is mounted on the valve stem and which incorporates said spray outlet region, said actuator assembly further incorporating a discharge conduit providing a communication between the stem flow conduit and the spray outlet region. The stem outlet flow conduit may be of circular-section as may be the discharge conduit. Preferably the flow and discharge conduits are of identical diameter, ideally in the range 0.5 mm to 1.5 mm. The flow and discharge conduit may each have a length from 3 to 50 times their diameter. The discharge conduit may, throughout its length, be collinear with the flow conduit. Alternatively the discharge conduit may be formed in two sections, namely a first section collinear with the flow conduit and a second section angled (e.g. perpendicular thereto). 
         [0041]    The spray outlet region may comprise a nozzle adapted to impart a swirling motion to the bubble laden flow prior to discharge thereof from the device. The nozzle may be a Mechanical Break-Up Unit. 
         [0042]    According to some embodiments, the aerosol spray device contains a material selected from the group consisting of pharmaceutical, agrochemical, fragrance, air freshener, odour neutraliser, sanitizing agent, polish, insecticide, depilatory chemical (such as calcium thioglycolate), epilatory chemical, cosmetic agent, deodorant, anti-perspirant, anti-bacterial agents, anti-allergenic compounds, and mixtures of two or more thereof. 
         [0043]    The present invention has been found particularly applicable in the case where the spray outlet region comprises a nozzle adapted to impart a swirling motion to the bubble laden flow prior to discharge thereof from the device. The nozzle may be a Mechanical Break-Up Unit, for which further detailed examples are given below. With such units, it has been found that good atomisation of the liquid being discharged is obtained, resulting in a fine spray. Aerosol spray devices in accordance with the invention are eminently suitable for use in conjunction with a variety of consumer products, e.g. air-fresheners, polishes, insecticides, deodorants and hairspray. 
         [0044]    The invention is particularly effective for spray devices where the spray outlet region comprises a nozzle adapted to impart a swirling motion to the bubble laden flow prior to discharge thereof from the device. The nozzle may be a conventional Mechanical Break-Up unit. Thus, the nozzle, may comprise a discharge orifice, a swirl chamber provided around the discharge orifice and one or more channels (“swirl channels” or “swirl arms”) extending outwardly from the swirl chamber. In such an arrangement, the flow conduit is in communication (e.g. via a discharge conduit in an actuator assembly) with the outer end(s) of the channel(s) so that the bubble laden flow is supplied to the swirl chamber for discharge through the orifice. 
         [0045]    The discharge orifice of the nozzle may, for example, have a diameter of 0.15-0.8 mm. There may be from 1 to 8 swirl channels each having a width of 0.1 mm-0.5 mm and a depth of 0.1 mm-0.5 mm. The swirl chamber may be circular with a diameter of 0.3 mm to 2 mm. 
         [0046]    The nozzle may comprise an insert having a face locating against a face of a boss in the spray outlet region of the device, wherein said discharge orifice is provided in the insert and wherein said faces of the boss and the insert are configured to define the swirl chamber and the channels. 
         [0047]    Such a valving arrangement of the first aspect of the invention is not limited in application to aerosol spray devices of the type defined in the second aspect of the invention, although they do have particular application thereto. Rather, the valving arrangements of the first aspect of the invention may be applied to any suitable aerosol spray device. 
         [0048]    As with one embodiment of the first aspect of the invention, a lower region of the valve stem may locate within the housing and the single seal may be mounted on the housing for relative sliding engagement with the valve stem. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0049]    The invention will be further described by way of example only with reference to the accompanying drawings, in which: 
           [0050]      FIG. 1  schematically illustrates a first known aerosol spray device, with a valve assembly having a pair of sealing gaskets; 
           [0051]      FIG. 2  schematically illustrates a second known aerosol spray device with a valve assembly having a single sealing gasket n; 
           [0052]      FIGS. 3 a  to 3 c    schematically illustrate a third known aerosol spray device, with an alternative valve assembly having a single sealing gasket formed from two adjacent parts; 
           [0053]      FIGS. 4 a  and 4 b    schematically illustrate a valve assembly in accordance with the invention in respective closed and open positions; 
           [0054]      FIG. 4 c    is a detail view of part of  FIG. 4 b   , showing the relative positions of an annular lip and a stem gas inlet; 
           [0055]      FIGS. 5 a  and 5 b    are perspective views of a cap part of the valve housing, showing gas flow conduits; 
           [0056]      FIG. 6  is a perspective view of a stem forming part of the valve assembly in accordance with the invention; and 
           [0057]      FIG. 7  is a cross section through the stem of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0058]    A valve assembly  200  according to the invention is illustrated in the accompanying  FIGS. 4 a    to  7 . Such a valve assembly is for incorporation into an aerosol spray device  1  of the type generally described in the introductory portion and comprising a container  2 , within which is a liquid  5  to be dispensed from the device by a pressurised gas such as nitrogen, air or carbon dioxide, which has limited solubility in the liquid  5  and is in a head space  6  of the container  2 . 
         [0059]    The valve assembly  200  of the invention would replace the valve stem  7  and housing  9  combination of the prior art, located between the dip tube  20  and the actuator  10 . 
         [0060]    The valve assembly  200  comprises a housing  202  with internal walls defining a valve chamber  204 , and a valve stem  220 . The housing  202  is formed of two portions: a lower, cup portion  206 ; and an upper, cap portion  208 . As described above by reference to the prior art, the valve assembly  200  would be crimped in place at the top of a container, with a distal portion of the valve stem  220  projecting from the top of the container for connection to an actuator. 
         [0061]    The cup portion  206  has a lower wall  210  with an aperture  212  therethrough. A tubular spigot  214  depends from the lower wall  210 . A dip tube (not shown) would be connected to the tubular spigot  214 , typically by means of an enlarged lower end as described by reference to the prior art of  FIG. 1 , the dip tube extending to the base of the container to which the valve assembly  200  is fitted. It will be appreciated that the lower region of a container to which the valve assembly  200  is fitted is in communication with the valve chamber  204  via the dip tube, spigot  214  and aperture  212  (which provides a liquid inlet for the valve chamber). 
         [0062]    The cap portion  208  comprises a generally cylindrical inner wall  224  from which a lip  226  projects inwardly at the upper end thereof. The lower end  228  of the cap portion has a narrower outer diameter so as to fit with an interference fit inside the cup portion  206 . At the upper end of the cap portion  208 , an annular rim  230 , together with an upper surface  232 , defines a shelf within which an annular sealing gasket  260  sits. 
         [0063]    A plurality of radial grooves  234  are defined between corresponding radial ribs  236  on the upper surface  232 . Inner ends  234   a  of the grooves  234  open into the upper end of the valve chamber, above the lip  226 . Outer ends  234   b  of the grooves  234  open into a circumferential groove  238 , which circumscribes the upper surface  232  just inside the rim  230 . The lower and side surfaces of the respective grooves  234 ,  238  are formed by the cup portion itself, whereas the upper surfaces thereof are formed by the lower surface  262  of the gasket  260 . 
         [0064]    A conduit  240  is formed through the cap portion  208 , with an upper end opening into the circumferential groove  238  via a hole  242 , and with a lower end exiting the side of the cup portion via a hole  244  in the outer surface thereof. It will be appreciated that the head space of a container to which the valve assembly  200  is fitted is in communication with the valve chamber  204  via the conduit  240 , circumferential groove  238  and radial grooves  234  (which together provide a gas inlet for the valve chamber). 
         [0065]    The valve stem  220  is generally cylindrical, having an outer surface  272  with a diameter equal to the inner diameter of the lip  226  such that the lip  226  forms a seal around the perimeter of the valve stem. A proximal end  274  of the valve stem is received in the valve chamber  204  and a distal end  276  projects through the centre  264  of the annular sealing gasket  260 , which is dimensioned to seal against the outer surface  272  of the valve stem  220 . The lower surface  262  of the gasket  260  defines the top of the valve chamber  204 . 
         [0066]    The valve stem  220  includes an outlet flow conduit  280  with an outlet aperture  282  at the distal end  276  and, more proximally, at least one first stem inlet  284  for liquid and at least one second stem inlet  286  for gas. As illustrated, there is a single stem inlet  284  for liquid and a single stem inlet  286  for gas, and they are positioned roughly in the middle of the valve stem, with the gas inlet  286  being slightly distal of the liquid inlet  284 . It will be understood that alternative arrangements are envisaged. For example, there could be multiple liquid inlets  284  and/or multiple gas inlets  286 ; the inlets  284 ,  286  could be located more proximally or more distally than shown; and the axial separation between the respective liquid and gas inlets could be greater than shown. 
         [0067]    Towards the proximal end  274  of the valve stem  220 , an enlarged shoulder portion  290  projects radially from the cylindrical valve stem  220 . The diameter of the shoulder  290  is substantially equal to that of the valve chamber  204 . A bore  292  runs centrally from the proximal end face  275  valve stem  220  to the shoulder portion  290 . Four conduits  294  extend radially within the shoulder portion  290  from the centre, where they open into the bore  292 , to the outside. At the outer ends, the radial conduits  294  open into respective axial grooves  296  in the outer surface of the shoulder  290  that run parallel to the bore  292  and to the outlet conduit  280 . 
         [0068]    As shown in the drawings, the valve stem  220  is biased upwardly of the valve assembly (and thus of the aerosol device) by means of a coil spring  222 . Lower end of coil spring  222  locates around the aperture  212  of the cup portion  206  of the housing  202 . In the closed valve position, as shown in  FIG. 4 a   , the shoulder  290  abuts against the lip  226  under the force of the spring  222 , and the flow channel defined by the bore  292 , radial conduits  294  and axial grooves  296  is blocked by virtue of the tops of the axial grooves  296  abutting against the underside of the lip  226 . Furthermore, the liquid inlet  284  is more distal than the sealing gasket  260 . Accordingly, there is no fluid communication between the valve chamber liquid inlet  212  and the outlet conduit  280 . There is also no fluid communication between the valve chamber gas inlet  234   a  and the outlet conduit  280 , because the gas inlet  286  is also more distal than the sealing gasket  260 , which hermetically seals against the outer surface  272  of the valve stem. 
         [0069]    The abutment of the shoulder  290  against the lip  226  acts as an upper limit stop, preventing the valve stem  220  from being urged further out of the valve housing  202 . 
         [0070]    When the valve stem is moved to the open position, as shown in  FIG. 4 b   , the stem liquid inlet  284  is moved below (i.e. proximal of) the lip  226  so as to be in fluid communication with the valve chamber liquid inlet  212  via the flow channel defined by the bore  292 , radial conduits  294  and axial grooves  296  through the stem shoulder portion  290 . Also, the stem gas inlet  286  is moved below (i.e. proximal of) the sealing gasket  260  to a position at the upper end of the valve chamber  204  in fluid communication with the valve chamber gas inlet  234   a.  At least a part of the stem gas inlet  286  must be open to the upper portion of the valve chamber  204  (i.e. the portion above the lip  226 ). Abutment of the bottom face  275  of the valve stem  220  against the lower wall  210  of the cup portion  206  defines a lower limit stop. 
         [0071]    Thus, to operate the device, an actuator cap  10  is depressed so that the valve stem  220  moves downwardly against the bias of spring  222  from the closed position to the open position. As a result, the liquid and gas stem inlets  284 ,  286  are displaced past the gasket  260  and brought into respective fluid communication with liquid (or powder)  5  from the container  2  and compressed gas from the head space  6 . 
         [0072]    Compressed gas can now flow into the outlet conduit  280  by passage through the hole  244  in the outer surface of the cap portion  208 , the conduit  240 , the hole  242 , the circumferential groove  238  and radial grooves  234 , and through the stem gas inlet  286 . 
         [0073]    Liquid  5  can now flow into the upper portion of the valve chamber  204  by passage upwardly along the dip tube  20 , through the inlet  212 , the bore  292 , the radial conduits  294  and the axial grooves  296 . Liquid  5  introduced into the upper portion of the valve chamber  204  passes via stem liquid inlet  284  into flow conduit  280  where it is mixed with the compressed gas bled through the stem gas inlet  286 . A bubble laden flow of homogeneous bubbles with similar diameters and without significant coalescence or stratification is formed in the outlet flow conduit  280 . 
         [0074]    That bubbly flow can then flow, preferably undisturbed, through the actuator  10 , such as one of the type disclosed in  FIG. 1 , to a spray outlet region  11 . This actuator cap  10  (which may be of the type available under the name “Kosmos” from Precision Valve (UK) Ltd) is moulded so as to locate on the top of valve stem  7 ,  220  and has an internal L-shaped conduit formed as a first section  12   a  collinear with the outlet bore  8 ,  280  of valve stem  7 ,  220  and a second section  12   b  that extends at right angles to section  12   a  and leads to spray outlet region  11 . Other different actuators could be used instead; a number of different exemplary styles are disclosed in WO 2011/061531 and WO 2011/128607. The substantially disturbance-free flow of the bubble laden flow can be achieved by configuring the outlet flow conduit  280  and the flow conduit through the actuator such that there is an absence of any flow disturbances, whereby the bubble laden flow is delivered to the spray outlet region in substantially the form in which it was created. 
         [0075]    The bubble laden flow should be at a velocity that gives a sufficiently short residence time of the flow in the outlet flow conduit  280  and the flow conduit through the actuator such that bubble coalescence or stratification does not occur. Typically the flow rate should be in the range 0.5 to 5 m/s. 
         [0076]    The bubble laden flow should be at between 1 bar and 20 bar pressure, and in a preferred embodiment for a consumer aerosol can, between 4 bar and 12 bar (said pressure reducing during evacuation of the can). 
         [0077]    The ratio of volume of gas/volume of liquid contained in the bubble laden flow in the outlet flow conduit  280  should be between 0.2 and 3.0 at the pressure prevailing in this conduit and more preferably between 0.3 and 1.3. 
         [0078]    Preferably, the conduits and outlet region (including any MBUs  13  that might be required) of the actuator  10  can be selected so as to be ideally suited to the flow and aerosolisation of whichever liquid (or powder) product is to be dispensed therefrom. 
         [0079]    Preferably, as shown in  FIG. 4 c   , the stem gas inlet  286  is moved to a position in which it is marginally offset distally from the lip  226 —i.e. a central axis  287  of the stem gas inlet  286  is just above the centreline  227  of the lip  226 . This allows not only gas from the valve chamber gas inlet  234   a  to enter the stem gas inlet  286 , but also a small amount of liquid from the valve chamber liquid inlet  212  too. 
         [0080]    Preferably, the stem gas inlet  286  is stepped, having an outer portion  286   a  (opening to the stem surface  272 ) with a larger diameter than an inner portion  286   b  (opening to the outlet conduit  280 ). Alternatively, the stem gas inlet  286  may have a conical cross-section, tapering from a larger outer portion to a smaller inner portion. The advantage of such gas inlet profiles is to assist in manufacture: when moulding the valve stem, pins are typically inserted into the mould to provide for the respective gas and liquid inlets. By having a tapered or stepped profile to the gas inlet, the corresponding pin can have a matching profile, thereby being thicker and stronger at its root than would be the case with a constant diameter pin (matching the narrowest diameter required for the gas inlet). However, a constant diameter gas inlet  286  could be used instead. 
         [0081]    In the construction of the valve assembly  200 , it should be ensured that the total cross-sectional area of the gas bleed passageways  240 ,  238 ,  234 ,  286  should not be so large that excessive gas is bled into the outlet conduit  280  such that the container  2  is depleted of pressurised gaseous propellant before all of the liquid  5  in the container has been discharged. Typically, the total cross-sectional area of the gas bleed inlet passageways should be equivalent to that of a singular, circular section inlet with a diameter of 0.15-0.8 mm. 
         [0082]    Preferred dimensions for the construction of the valve assembly  200  to ensure production of a bubble laden flow of homogeneous bubbles with similar diameters and without coalescence or stratification are shown in the following table: 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                 Reference 
                 Diameter 
                 Length 
               
               
                 Item 
                 Numeral 
                 (mm) 
                 (mm) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Stem 
                   
                   
                   
               
               
                 Portion of valve stem 
                 272 
                 3.2 
                 11.4 
               
               
                 above shoulder 
               
               
                 Portion of valve stem 
                 274 
                 3.5 
                 3.65 
               
               
                 below shoulder 
               
               
                 Stem shoulder portion 
                 290 
                 4.7 
                 1.0 
               
               
                 Outlet conduit in valve 
                 280 
                 1.0 
                 10 
               
               
                 stem 
               
               
                 Stem liquid inlet 
                 284 
                 0.5 
                 1.1 
               
               
                 Stem gas inlet 
                 286 
                 0.2 
                 1.1 
               
               
                 Outer portion of stem 
                  286a 
                 0.5 
                 0.7 
               
               
                 gas inlet 
               
               
                 Inner portion of stem 
                  286b 
                 0.2 
                 0.4 
               
               
                 gas inlet 
               
               
                 Distance of stem gas 
                   
                   
                 7.8 
               
               
                 inlet from distal end of 
               
               
                 stem 
               
               
                 Distance of stem liquid 
                   
                   
                 8.6 
               
               
                 inlet from distal end of 
               
               
                 stem 
               
               
                 Stem bore 
                 292 
                 1.0 
                 4.4 
               
               
                 Radial conduit 
                 294 
                 0.5 
                 1.6 
               
               
                 Axial groove 
                 296 
                 0.5 (0.25 radius) 
                 1.0 
               
               
                 Housing 
               
               
                 Cup portion outer 
                 206 
                 12 
                 5.4 
               
               
                 diameter 
               
               
                 Cup portion inner 
                   
                 8.0 
                 4.2 
               
               
                 diameter 
               
               
                 Spigot 
                 214 
                 4.0 
                 4.8 
               
               
                 Aperture 
                 212 
                 2.0 
                 6.0 
               
               
                 Cap portion lower end 
                 228 
                 8.0 
                 4.2 
               
               
                 Inner wall 
                 224 
                 4.8 
               
               
                 Lip 
                 226 
                 3.2 
                 0.91 
               
               
                 Rim 
                 230 
                 11.5 
                 1.1 
               
               
                 Circumferential groove 
                 238 
                 9.1 
                 0.5 (width); 
               
               
                   
                   
                   
                 0.2 (height) 
               
               
                 Gas hole 
                 242 
                 0.5 
               
               
                 Gas hole 
                 244 
                 0.5 
               
               
                 Conduit 
                 240 
                 0.5 
               
               
                 Radial groove 
                 234 
                 0.5 
               
               
                 Offset: stem gas inlet to 
                 227/287 
                   
                 0.06 
               
               
                 lip (in open position) 
               
               
                   
               
             
          
         
       
     
         [0083]    With the dimensions as indicated above, the valve assembly  200  is particularly suitable for consumer aerosol products such as polishes, insecticides, deodorants, hairspray and air fresheners. 
         [0084]    It will be appreciated that the specific dimensions and arrangement of the various constituent parts of the respective gas and liquid flow paths are by way of example only and that alternative arrangements are envisaged. What is key is for the valve chamber gas inlet  234   a  to be distal of the lip  226  and for the valve chamber liquid inlet  212  to be proximal of the lip  226 , whilst the stem gas and liquid inlets are positioned such that the stem liquid inlet is brought into fluid communication with the valve chamber liquid inlet and the stem gas inlet is brought into fluid communication with the valve chamber gas inlet on actuating the valve to the open position. 
         [0085]    In particular, the arrangement of the flow passage  292 ,  294 ,  296  through and past the stem shoulder portion  290  could be omitted, so long as the stem liquid inlet is only brought into fluid communication with the valve chamber liquid inlet in the open position; the flow path being blocked by virtue of the lip  226  when in the closed position. 
         [0086]    Also, whereas the valve assembly is described as having four radial conduits  294  and associated axial grooves  296 , there may be fewer or more. Likewise, four radial grooves  234  are illustrated, but there may more or fewer. 
         [0087]    Furthermore, although described as generally cylindrical, the stem  220  may take other generally prismatic profiles (such as square), with appropriate adaptation of mating parts such as the gasket  260  and the lip  226  and the inner walls  224  of the cap portion  208 . Similarly, the shape of the outer surface of the housing  202  does not have to be generally round in cross-section. 
         [0088]    For a given exit orifice size the dependency of gas and liquid flow rates on gas and liquid inlet diameters is complex; for example it is proposed that reducing the liquid inlet diameter produces a lowering of pressure inside the conduit which increases the inflow of gas into the conduit. However this increased gas inflow can increase the blockage of the bubbly flow at the swirl inlets and exit orifice of an MBU, which produces a lowering of the liquid inflow rate from the value expected. 
         [0089]    To minimise the droplet sizes it is necessary to maximise the gas/liquid volume ratio however smaller exit orifices and higher canister pressures also reduce drop size. The ratio of volume of gas/volume of liquid contained in the bubble laden flow in the flow conduit should typically be between 0.2 and 3.0 at the pressure prevailing in this conduit and more preferably between 0.3 and 1.3, although ratios as high as 9.0 can still produce satisfactory results. 
         [0090]    Method of Assembly 
         [0091]    In known valve assemblies, such as those described by reference to the accompanying  FIGS. 1 and 2 , the stem  7  is typically inserted into the housing  9  from above (after dropping in the spring  14 , or having already attached the spring to the bottom of the valve stem), and the assembly  3  can then be crimped together with the top cap  30 , securing the sealing gasket(s) in place and securing the assembly to a container  2 . By virtue of the lip  226 , and the shoulder  290  of the present invention, it would not be possible to insert the valve stem  220  into the housing  202  from above. Accordingly, a modified assembly process is carried out. 
         [0092]    In essence, assembly is initially carried out upside-down. Reference to upper and lower portions, etc., should be taken as references to those portions in their usual orientation in use (i.e. an upper portion is closer to the top of a valve assembly and to the outlet spray region of a container to which it is attached than a lower portion). 
         [0093]    Thus, to assemble a valve assembly  200  according to the invention, a gasket  260  is placed into the central portion of an inverted top cap  30 , and an inverted valve cap portion  208  is placed on top, so that the gasket  260  is held in place between the top cap  30  and the shelf on the ‘upper’ surface  232 . A valve stem  220  is inserted, distal end  276  first, through the cap portion  208  in the direction from the narrower ‘lower’ end  228  towards the upper surface  232 . The distal end  276  passes through lip  226  with an interference fit until the shoulder  290  abuts against the lip  226 . The spring  222  can then be slid over the ‘lower’ proximal end  274  of the valve stem. Alternatively, the spring  222  could be inserted together with the stem  220 . The cup portion  206  can then be snap-fitted onto the cap portion  208 . 
         [0094]    The assembled top cap  30 , housing  202  and stem  220  can then be inverted (to the upright orientation) for crimping of the central portion of the top cap  30 , to secure the cap portion  208  thereto, ensuring that the hole  244  is not obstructed by the crimped top cap  30  to ensure that the gas flow passageway is viable. A dip tube  20  can then be secured to the spigot  214  at the bottom of the cup portion  206 . 
         [0095]    Alternative orders of the assembly steps can readily be envisaged, such as assembling the cup and cap portions  206 ,  208  of the valve housing together (after the insertion of the stem  207  and spring  222  into the cap portion  208 ) prior to placement onto the top cap  30  with gasket  260 , or placing the gasket  260  on to the top of the assembled cup and cap portions after having been inverted to the upright orientation, then placing the top cap  30  over the gasket and valve housing combination prior to crimping. Moreover, the crimping step and the fitting of the dip tube could instead take place with the assembly in an inverted orientation.