Field of invention

This invention concerns flow discharge control devices, sometimes referred to as regulators for controlling the flow of fluids (usually in the form of atomised droplets) from pressurised containers, and to a method of so regulating flow.

Background to the invention

In view of the resistance to the continued use of chlorofluorocarbons (CFCs) as propellants in so-called aerosols (pressurised containers for dispensing and atomising liquids), other propellants have had to be considered. Low boiling point gases such as propane, butane and di ethylether have been used, but have other disadvantages which render them undesirable for this particular purpose.

The advantage of using a low boiling point gas (which is in. liquid form at normal ambient temperatures), is that a constant pressure within the container is maintained whilst any of the liquid gas remains in the container, so ensuring a relatively constant propellant pressure source throughout the whole of the discharge life of the container. This advantage is not realised if a permanent gas such as nitrogen is used as the propellant. If such a gas is used, the propellant pressure drops during. the

discharge due to the increasing volume which it must occupy as the liquid is to be discharged from the container.- Since the temperature remains approximately constant, the decrease in pressure is substantially proportional to the increase in volume within the container. The reducing pressure results in a change in spray characteristics such a spray angle, droplet size and distribution.

A number of regulators have been proposed to provide constant mass flow rate by compensating for the falling pressure, but most have involved moving parts such as spring loaded pistons which increase costs and decrease reliability; and it is an object of the present invention to provide a regulator or discharge valve, and a method of so regulating flow, which will produce a substantially constant spray characteristic over a considerable range of propellant pressure.

Summary of the invention

According to one aspect of the present invention there is provided a discharge valve for regulating the flow of a liquid product from an aerosol container pressurised substantially by a permanent gas propellant and comprising:

(a) first passage means for conveying the liquid under gas pressure to a mixing region,

(b) second passage means for conveying the pressurised gas separately from the liquid into the mixing region,

(c) an exit nozzle through which the mixture of liquid and gas is forced to exit from the container, and

(d) at least one intermediate restrictor between the mixing region and the exit nozzle through which the

mixture of liquid and gas is forced to pass, wherein:

(e) the relative size of the restrictor is selected to ensure that at least substantially choked or sonic flow results through the restrictor.

The dimensions of the exit orifice are chosen to ensure the required spray characteristics.

The term choked flow in this context means that the flow through the nozzle is sonic. This phenomena of choked liquid/gas mixed flow is described inter alia by J F Muir et al in an article entitled "Compressible flow of an air/water mixture through a vertical two-dimensional converging diverging nozzle", published in the proceedings of the 1963 Heat Transfer and Fluid Mechanics Institute, edited by A Roshko et al, 1963 and by L.van Wijngaarden, in a paper entitled "One-Dimensional Flow of Liquids Containing Small Gas Bubbles", 1972.

The pressurised liquid is preferably forced into the mixing chamber via a flow controlling orifice which may be formed in a narrow bore dip-tube.

The pressurised gas is also preferably conveyed through a small orifice into the mixing chamber, again for the purpose of controlling the flow rate.

The mixing chamber may be cylindrical in shape.

Where a dip tube is employed the mixing chamber may be formed as an extension of the dip tube.

The second passage means may be formed in the dip tube;

and the dip tube may be porous, thereby constituting the first passage means.

Alternatively the second passage means may comprise a porous membrane.

The diameter of the or each intermediate restrictor is preferably in the range 10% to 60% of the diameter of the cylindrical mixing chamber.

In absolute terms the diameter of the intermediate restrictor for ordinary applications will generally be in the range 0.2 to 1.2mm.

In some arrangements it may be advantageous for the restrictor to be in the form of a capillary tube.

According to a preferred feature of the invention the pressurised gas (which is supplied to the mixing chamber) may also be employed to pressurise the liquid (to force it into the mixing chamber).

By ensuring good mixing in the mixing chamber and by ensuring that the residual pressure which remains across the (or each) intermediate orifice when the liquid content is about to become exhausted, is still sufficiently high to produce at least substantially choked flow through the intermediate orifice (or each intermediate orifice) and thereby produce a shock wave after each orifice, the form and characteristics of the final spray at the exit orifice are found to remain essentially constant throughout the discharge of the liquid content.

Thus the exit orifice is presented with a foaming mixture

similar to that normally produced by liquifi'ed' gas propellants as- they start to boil or evaporate upstream of the exit nozzle.

In some applications, it may be desirable to limit the lreduction of liq-uid exhausted via the exit orifice during ^J the discharge life of the container.

Whilst it is virtually impossible to achieve no change in the liquid flow through the exit orifice with decreasing propellant pressure, it is believed that any variation can be significantly reduced if:

(1) the pressure drop between the propellant pressure and mixing region pressure is kept as small as possible;

(2) the pressure drop produced by the flow of liquid is essentially due to a velocity increase due to a decrease in passage diameter; and

(3) the second passage means delivering the gas to the mixing region essentially creates laminar flow conditions in the gas.

By using different flow type passages obeying different physical laws, the proportion of gas/liquid can be selected so as to alter (and if desired limit) the liquid flow reduction via the exit nozzle, by compensating for the effect of pressure reduction on flow through the choked intermediate restricto (s) .

The critical pressure ratio needed to achieve choking in any liquid/gas mixture is in general a function of

pressure and volumetric mixture proportions and can if necessary be determined by experiment. A minimum sonic velocity (and-hence pressure ratio) is usually achieved at mixtures of approximately 50% gas and 50% liquid.

In accordance with another aspect of the present invention in a discharge valve of a type as defined in sub- paragraphs (a) to (d) above, the size of the passage means are so selected in relation to the size of the intermediate restrictor that the volumetric ratio of gas to liquid dispensed at atmospheric pressure is less than approximately 5:1.

Where it is desirable that the discharge is to be unaffected by the attitude of the container, the liquid may for example be contained in a collapsible sachet within the container and subjected to the pressure of the gas occupying the space between the sachet and the container wall, to thereby pressurise the liquid within the sachet. This arrangement also prevents loss of propellant gas in the event that the release valve is operated whilst the container is upturned, as would otherwise be the case.

Conventional aerosol dispensers use a volatile propellant such as a liquefied chlorofluorocarbon and incorporate a normally closed on/off valve associated with a dip tube up through which liquid passes when the valve at the top is opened. A push-on nozzle containing a small orifice completes the discharge passage and atomisation can be achieved if the size of the outlet orifice is selected accordingly.

According therefore to a further aspect of the present

invention there is provided a kit of parts which enables an aerosol-type dispenser valve to be modified so as to work with a nonvolatile propellant such as a pressurised permanent gas. Such a kit of parts may contain a housing adapted at one end for fitting to an aerosol release valve (in place of the conventional dip tube) and adapted at its other end to receive and be fitted to the upper end of the removed dip tube (or an equivalent tube), wherein the housing includes a mixing chamber, first passage means for conveying pressurised gas into the mixing chamber, second passage means through which pressurised liquid can enter the mixing chamber, and at least one orifice between the mixing chamber and the aerosol release valve the dimensions of which are chosen to ensure that at least substantially choked flow results through the orifice.

Although the valve of the present invention is particularly suited for use with a single permanent gas such as nitrogen, other gases such as air, CO _ or NAO may also be used either alone or in suitable mixtures. such gases may even be used in combination with a liquefied propellant; however the proportion of the latter at atmospheric pressure should preferably not exceed about 10%.

The invention will now be described, by way of example, with reference to the accompanying drawings.

In the drawings:

Fiqure 1 is a schematic representation of a flow discharge control device fitted within a canister containing liquid for dispensing through an outlet nozzle; Figure 2 is a schematic diagram of another flow discharge

control device fitted to a similar canister but in which the liquid contents are separated from the propellant gas by a collapsible impervious sachet;

Figures 3a and 3b are schematic diagrams respectively showing an aerosol-style discharge valve in the closed and open positions, the valve being modified in accordance with the invention to enable a nonvolatile propellant gas to be used to force liquid through the valve and from thence through an exit nozzle; and

Figure 4 is a schematic diagram of a discharge valve in the closed position, being similar to the valve of Figure 3a but including reference characters for the dimensions of certain parts having critical dimensions.

Detailed description of the drawings

Referring to Figure 1, the device comprises a body 10 having two restrictions 11 and 12, one for restricting the passage of a liquid product to be dispensed and the other restrictor 12 for restricting the passage of gas into a central mixing chamber 13. This mixing chamber exits through a choke orifice or restrictor 16 designed to provide sufficient pressure drop to ensure violent turbulent mixing and choked flow in the mixture exiting from the mixing chamber 13. At a region downstream of the orifice 16 the flow becomes supersonic and shock waves are produced as the flow subsequently goes from supersonic to subsonic, producing vigorous break-up of gas particles to form a uniform foam. Additionally the orifice 16 reduces the pressure in the mixture, thus causing the gas to expand and increasing the ratio of gas to liquid.

The liquid 17 and gas 18, at an initial pressure Pi, are contained within a closed vessel 20, typically a metal or plastics canister. When a control valve 15 is opened, liquid is forced up the tube 11 containing the liquid restrictor to enter the mixing chamber 13, and in turn gas can pass through the passage 12 containing the gas restrictor also to the mixing chamber. The mixture, now at a pressure P2, is forced through the mixing orifice 16 where the gas content of the mixture expands due to pressure drop, and the gas bubbles break-up to form a foam due to the vigorous turbulent mixing action caused by the sudden expansion from the restriction introduced by the orifice 16 and by passing through shock waves downstream of the orifice. Finally the mixture is forced through an exit nozzle 21 in a nozzle head 14 which constitutes the last restriction to the low, and which is selected to give uniform spray characteristics.

The sizes and characteristics of the passages 11 and 12 are arranged so that the liquid/gas mixture passing through the mixing orifice 16 is of a ratio that will ensure that sufficient gas is left over when the liquid in the vessel 20 has been expended, and that during use full atomisation and violent mixing takes place at the exit of the mixing orifice 16 so that the mixed flow is choked in the ther odynamic sense. In other words, the mixed flow is sonic at the exit from each restrictor (or the passage where the latter serves as the restrictor), becomes supersonic and returns to subsonic as it passes through a shock wave at a distance downstream from the exit.

Figure 2 of the drawings shows an alternative form of construction in which the regulator exit nozzle 21 and control valve 15 are the same as in Figure 1, as also is

the canister 20. However, the liquid 17 is now contained within a collapsible sachet or bag 22 and the pressurised gas occupies the space 18 around the outside of the bag between the bag and the canister wall. The arrangement has the advantage that the liquid can be dispensed irrespective of the angle of the canister, whereas proper dispensing of the liquid and gas mixture will occur only if the canister is substantially upright when the Figure 1 embodiment is used.

As an alternative to the sachet 22, a ball valve or similar type of check valve may be employed to prevent loss of gas if the canister is inverted.

Figures 3a and 3b show another flow control valve such as might be employed in a conventional aerosol dispenser which has been modified in accordance with the invention.

Referring first to Figure 3a, a canister 24 is sealed to the upper end of a tubular housing 26 which contains an annular ledge intermediate its ends at 28 against which a seal 30 rests when the valve is in its upper closed position. The seal itself is secured around the upper end of a cup 32 which is fitted to and encloses the lower end of a central tube or valve stem 34.

Just above the seal 30 and in the wall of the tube 34 is a liquid orifice 36. In the closed position shown, the orifice 36 is separated by the seal 30 from the liquid product which is forced up a dip tube 38 under the action of a permanent gas propellant, such as nitrogen, contained above the liquid within the canister 24. If the tube 34 is depressed against a return spring 40, the liquid orifice 36 is exposed and liquid can enter the tube 34

through the orifice 36 from the upper end of the dip tube 38.

A gas orifice 42 is provided in the wall of the tube 34 remote from the orifice 36 and a second seal 44 serves to separate the orifice 42 from gas under pressure when the tube 34 is in its upper closed position as shown in Figure 3a. The housing 26 includes apertures around its intermediate region of which two are shown at 46 and 48 to allow pressurised gas to enter a spring chamber 50 containing the spring 40.

When the central tube 34 is depressed, as shown in Figure 3b, the orifice 42 communicates with the pressurised gas in the spring chamber 50 and the gas entrains and mixes with the liquid passing through the tube which has entered via orifice 36. An exit head 14 containing an exit nozzle 52 is fitted to the upper end of the tube 34 in known manner.

Between the mixing chamber 54 and the exit nozzle 52 are located three intermediate chokes or restrictors 56, 58 and 60. At least the upper restrictor 60 may, if desired, be formed integrally within the exit head 14. The restrictors 56 to 60 cause progressive expansion of the gas content of the mixture and progressively better ato isation of the liquid content of the mixture, their size of being chosen to cause violent turbulent mixing.

Tests have shown that with the modified dispenser described, the volumetric ratio of gas to liquid exiting at atmospheric pressure will be less than about 5:1, in contrast to the far higher ratios of known aerosol dispensers using typical liquified propellants. With certain

products, such as hair sprays or furniture polishes, the present ratio may be only 1:1, and with other products it is envisaged that the ratio may be even as low as 0.25:1.

The position of at least the lower restrictor 56 is so selected, relative to the position of the gas orifice 42, that the orifice 42 is located substantially nearer to the restrictor 56 than to the liquid orifice 36.

Figure 4 shows a flow control valve, similar to the valve of Figure 3a, with reference characters for the dimensions of major parts (such as the orifices and restrictors previously described above) whose sizes are important and may be critical. Table 1 below gives the dimensions of the identified parts expressed as a range of sizes which have been found in practice to work successfully. The table also indicates the preferred ranges of some critical diameters.

More than one gas orifice may be provided in the central tube (and likewise more than one liquid orifice); and it has been found that the preferred ratios of the cross- sectional areas of the liquid orifice(s) to the gas orifice(s) should be within the range of about 10:1 to 400:1.

It should be noted that three restrictors are shown in Figure 4, and their spacings from the centre of the gas restriction orifice (diameter E) are given in ascending order (upwards) as dimensions C, B and B, respectively. Where only two restrictors are required, the one indicated at B, is omitted. Where only one restrictor is required the one indicated at C only is retained.

TABLE 1

DIMENSION RANGE COMMENTS

B 8-25mm

Bl 12-25τnm

C 0-25mm Preferred size less than 3.0mm D l-3mm

E 0.1-0.25mm Preferred size

0.16 to 0.21mm F 0.5-4mm

G 0.5-4mm

I l-7mm Preferred size

3 to 5mm S 10-30mm

SI 3-6mm

T 0.5-2mm Length of gas bleed orifice (dia. E)

X,Y,Y1 0.1xD-0.75xDmm Preferred size

0.15xD to 0.6xDmm

Z l-3mm More than one liquid orifice can be used

Table 2 below, gives examples of the dimensions of three arrangements of valves which have been tested. In Example 1 two restrictors were used (ie those having the spacings B and C), while in Examples 2 and 3 three and one restrictors were used respectively.

- TABLE 2

DIMENSION Example 1 Example 2 Example 3

(2 restrictors) (3 restrictors) (1 restrictor)

A 14.2

B

Bl

C 6.2

D 1.6

E 0.20

F

G 1.0

H 36.5

I 3.8

S 22.0

SI 3.5

T 4.0

X 0.5

Y

Yl

Z 1.6

All dimensions are expressed in millimeters.

In each example of Table 2 the spray nozzle used was a Precision Valve "Kosmos" of the Mechanical break-up C02 type and of 0.35mm (0.013in) nozzle diameter. The liquid used was a 50% mixture of Propan-ol-2 with water, with the starting pressure in each example being 8 bar (gauge). The mean flow rates, which varied by 50% from start to finish, were as follows:

Example 1 : Iml/s Example 2 : 0.85ml/s Example 3 : 1.3ml/s