WO1993024238A1

WO1993024238A1 - Fluid delivery systems

Info

Publication number: WO1993024238A1
Application number: PCT/GB1993/001023
Authority: WO
Inventors: Ian Michael Daines Gaylor; Clive Patrick Ashley Catterall
Original assignee: Cambridge Consultants Limited
Priority date: 1992-05-22
Filing date: 1993-05-19
Publication date: 1993-12-09
Also published as: AU4081793A

Abstract

A fluid delivery system which comprises a variable volume reservoir into which fluid is drawn through a valve means and pressurised and from which fluid is forced out through a second valve means to be discharged through an outlet nozzle. In an embodiment the reservoir (24) is formed between lower and upper rolling diaphragms (20, 22), and a rotary cap (18) is operable to move the first diaphragm up and down, in the former case to depressurise the reservoir and cause fluid to be drawn into the reservoir through a valve (52, 54) associated with the lower diaphragm, and in the latter case to pressurise the drawn in fluid, so that a manually operable valve (58, 64) associated with the upper diaphragm can be operated fully to discharge the pressurised fluid through an outlet nozzle (27) due to the action of a spring (53) acting on the lower diaphragm.

Description

Title: Fluid delivery systems

Field of invention

This invention concerns fluid delivery systems for dispensing liquids, gels, creams and the like either as such or in the form of a spray or mist made up of small droplets.

Background to the invention

In order to dispense a fluid in the manner aforesaid a degree of pressurisation is required to force the fluid through an exit nozzle. Hitherto it has been commonplace to store the fluid in a pressurised container together with a low boiling point gas which serves as a fluid spring acting either directly or through a diaphragm onto the fluid which is to be dispensed. The need for a pressurised container tends to restrict the shape of the container. Additionally suitable low boiling point gases have either been found to be environmentally damaging or are flammable or have other undesirable characteristics.

It is therefore an object of the present invention to provide an alternative fluid delivery system which does not incorporate a pressurised gas and therefore does not require a pressure vessel.

Summary of the invention

According to the present invention a fluid delivery system compr ises :

(a) cannister means

(b) a variable volume reservoir located therein

(c) valve means for controlling the flow of a fluid contained within the reservoir through an outlet nozzle

(d) spring means within the cannister acting on the reservoir to pressurise the contents thereof so that when the nozzle valve is opened the contents are forced therethrough.

In one embodiment of the invention, the reservoir is formed between two rolling diaphragms, one of which is acted on by spring means fixedly arranged within the cannister and the other of which is movable away from and towards the first mentioned diaphragm by upward and downward movement of a cap displaceably fitted to the upper end of the cannister with means for retaining the cap in the lower position, and one way valve means is provided admitting fluid together with the reservoir through the first mentioned diaphragm and manually operable valve means associated with the second diaphragm to permit the exit of fluid from the reservoir through the discharge nozzle.

Operation of this embodiment is achieved by unlatching and lifting the displaceable cap, and thereby the upper diaphragm, relative to the lower diaphragm, thereby creating a pressure drop within the reservoir between the two diaphragms causing fluid to be sucked into the reservoir with continued upward movement of the cap. The fluid within the reservoir is prevented from leaving the latter during subsequent downward movement of the cap and where the fluid is essentially incompressible, during this downward movement the lower diaphragm is displaced downwardly against the action of the spring means. The latter therefore pressurises the contents of the reservoir so that upon release of the second mentioned valve means, fluid will be forced under pressure from the reservoir through the exit nozzle. Discharge of fluid from the reservoir reduces the volume within the reservoir enabling the lower diaphragm to move in an upward sense under the action of the spring until the reservoir has been essentially emptied.

The one way valve means may comprise apertures in the first mentioned diaphragm cooperating with aperture means at the head of a hollow diaphragm support through which fluid can pass from the main fluid reservoir within the cannister.

The second mentioned valve means may comprise apertures in the second mentioned diaphragm which is normally impaled against the underside of another hollow piston like member due to the excess pressure within the reservoir, and the valve operating means is a peg or plunger which can be depressed in a downward direction manually so as to push the second mentioned diaphragm away from its supporting surface to enable fluid to pass through the apertures into a space communicating with the exit nozzle.

Preferably support means is provided at an intermediate position between the two diaphragms which engages at least peripheral regions of the diaphragm when the latter are in their maximum displacement position (downwardly in the case of the second mentioned diaphragm and upwardly in the case of the first mentioned diaphragm) . Since removal of fluid from the cannister will tend to create a vacuum, preferably venting means is provided to enable the pressure within the cannister to be balanced to atmospheric pressure. Typically valve means is associated with the vent to enable air to enter the cannister but to prevent fluid from leaving it.

According to a second embodiment of the invention, the reservoir is formed between a first piston acted on by spring means urging it in an upward sense and a second piston movable both upwardly and downwardly relative to the lower piston by upward and downward movement of a cap associated with the cannister, valve means associated with the first piston permitting fluid to pass from below to above the piston but not in the opposite sense if pressure above the piston exceeds that below the piston, and second valve means openable by manually depressing a release button, permits fluid under pressure to pass from the region between the two pistons through an exit nozzle.

Preferably means is provided for locking the cap in its lower position.

In use, with the space between the two pistons devoid of pressurised fluid, upward movement of the cap and second piston associated therewith will cause fluid to be drawn into the space between the two pistons until the cap and said second piston reach the position of maximum upward displacement. Thereafter where the fluid is imcompressible downward pressure on the cap will force the charge of fluid and the first mentioned piston in a downward sense as the piston associated with the cap is moved down, thereby compressing a spring means acting on the underside of the first mentioned piston. After locking the cap in its lowered position, operation of the valve means associated with the second mentioned piston enables fluid now under considerable pressure due to the compressed spring, to leave through the exit nozzle. Discharge of the fluid from the space between the two pistons causes the spring means to extend and move the lower piston in an upward sense until the lower piston is prevented from moving upwardly any further.

The space between the two pistons can be replenished with fluid by repeating the aforementioned process.

As with the first mentioned embodiment, venting means is provided if the reduction in volume of the fluid within the cannister will otherwise create a vacuum.

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

Figure 1 is a cross-sectional view of a fluid discharge system embodying a first aspect of the invention in which the fluid reservoir is made up of two rolling diaphragms;

Figure 2 is a scrap view of the lower end of the discharge nozzle shown inverted to reveal detail;

Figure 3 is a similar cross-sectional view of a fluid discharge system embodying a second aspect of the invention in which the reservoir is formed between two opposed pistons; and

Figure 4 is a scrap cross-sectional view showing the cross piece in between the two pistons of the arrangements shown in Figure 3 .

Detailed description of drawings

The fluid discharge system shown in Figure 1 is intended to be fitted to a container or cannister only part of which is shown and will be referred to later. The cannister contains fluid such as a liquid or cream or gel which under normal circumstances has to be dispensed in relatively small quantities through an outlet nozzle at the top of the device. Depending on the material in the cannister the output will either comprise fine spray (as in the case of hair spray or furniture polish), or a quantity of a gel or cream which may be foamed as for example in the case of soaps and shaving creams and the like.

The system thus comprises a fluid container the upper neck region of which is shown at 10, the upper end of which is threaded at 12 to receive an internally threaded sleeve 14. An upper section 16 of the sleeve is formed with reduced diameter and is externally threaded, having a diameter and thread profile which is preferably different to the thread profile 12. A cap generally designated 18 also in the form of a cylindrical sleeve is internally threaded to engage the screw thread on the section 16.

As will be described in more detail later, a locking device is provided to prevent the sleeve 14 from being accidentally unscrewed and stop means is provided which may be overriden to limit the rotation of the cap 18 relative to the section 16. Typically the stop means limit the rotation to less than 360°. Within the assembly are mounted two rolling diaphragms, a lower one 20 and an upper one 22. Both are trapped and sealed peripherally to define a chamber 24 which can be pressurised and upon displacement of the seals can accommodate a volume of fluid under pressure for subsequent discharge.

Within the cap 18 is located a spray head 26 containing an outlet orifice 27 through which fluid under pressure can exit and depending on the type of fluid so the spray head will include droplet forming devices or foaming devices or simply comprise passage means for delivering liquid to the outlet aperture 27.

Typically the cap 18 is cut away at the upper end to define two side cheeks one of which is shown at 28 and the spray head 26 is located between the two cheeks and can be depressed in a downward direction (see arrow 29) relative to the side cheeks such as 28 to operate the device. The side cheeks prevent accidental operation of the device since they protect the spray head 26 against endwise force which might otherwise operate the device.

An apertured plate or washer 32 is located between the two rolling diaphragms and is peripherally sealed thereto. The washer and the rolling diaphragm edges are trapped between the upper end of the threaded end 12 of the neck 10 and a lower circular edge of the upper threaded member 16 which when the item 14 is screwed into place automatically traps the peripheral regions of the rolling diaphragms and washer 32.

The spray head 26 includes a central cylindrical housing 30 of smaller diameter than the upper section which is in the form of a top hat the sides of which are cut away leaving a plurality of equally spaced fingers such as 31 and 33 the lower ends of which extend radially outwardly to engage slots in an intern central cylindrical sleeve 35 formed integrally with the cap 18. Engagement of the fingers 31, 33 etc with the upper ends of the slots as shown determines the upper position of the spray head 26.

Supported in an inturned annular flange 34 is a cup shaped piston 36 into which the housing 30 protrudes and as will be described later is a sliding sealing fit therein. The cup 36 is fitted within the upper rolling diaphragm 22 and the latter is lightly attached thereto by means of a peripheral protrusion 37 at the lower end of the cup.

The locking device for securing item 14 on the neck comprises lugs 38 and 40, one carried by the neck and the other internally of the sleeve 14. The lugs are positioned on the two members so that they engage only when the item 14 has been screwed onto the neck and by providing a ramp surface on one or both of the lugs in the appropriate direction so the lugs ride up and over one another as the sleeve 14 is screwed into position but any attempt to reverse rotate the sleeve 14 relative to the neck 10 is prevented by engagement of the two lugs 38 and 40.

By forming the sleeve 14 from resilient plastics material it is possible to distort the latter into an oval shape and cause the lugs 38 and 40 to clear one another to permit reverse rotation when for any reason it is necessary to remove the item 14 and the rest of the discharge assembly from the neck 10. However under normal circumstances the two lugs engage and prevent any such removal .

Within the neck 10 is located a stepped sleeve generally designated 42 which serves to accommodate the lower rolling diaphragm 20 in its upper region and a support and compression spring (to be described later) within its lower section.

Rotation of the cap 18 relative to the threaded section 16 of item 14 is controlled by the inter-engagement of two lugs 44 and 46 situated on the two members 16 and 18. Typically rotation is restricted to just less than 360°. The pitch of the thread between the caps 18 and the threaded section 60 and the internal diameter of the member 16 are selected so as to ensure that a single rotation of the cap 18 will introduce the desired volume of fluid into the chamber 24. If a single rotation is insufficient, the lugs 44 and 46 must be arranged in such a way that for example two or even three rotations of the cap 18 are permitted before the stops engage.

As with the sleeve 14, the cap 18 may also be formed from resilient plastics material enabling it to be distorted into an oval shape to permit overriding of the abutments 44 and 46 in the event that the cap 18 is to be removed.

The remaining constructional features of the system shown in Figure 1 will best be described in relation to the use and operation of the device.

Initially it is assumed that the upper diaphragm 22 occupies the position shown in Figure 1 and the lower diaphragm 20 is displaced upwardly to be in contact with the washer 32. The chamber 24 is now of minimal volume. From this start position, cap 18 is rotated so as to lift rolling diaphragm 22 relative to diaphragm 20. This is achieved through the engagement between the cap 18 and the member 36 and the engagement of the diaphragm 20 with the member 36.

The need for washer 32 is now evident. Its presence prevents the peripheral region of the generally flattened surface of the lower rolling diaphragm 20 from lifting but leaves the central region 21 of the diaphragm 20 free to lift as the pressure within the chamber 24 drops due to the lifting of diaphragm 22.

Elevation of the central region 21 enables fluid to be drawn into the chamber 24 from the cannister. The fluid passes through a diptube 48 up through the central hollow stem 50 of the lower diaphragm support 51 and because the central region 21 has been lifted off the latter, the fluid can pass as shown by the arrow A over the weir and into an annular groove 52 within the face of the support 51 to exit through apertures such as 54 and 56 in the surface of the rolling diaphragm 20 which are arranged in a circle and register with the groove 52.

Continued upward movement of the cap 18 and diaphragm 22 fills the space 24 with fluid.

Since cap 18 can only be rotated by an amount determined by the end stops 44 and 46, provided the cap is rotated fully to the end stop position, the volume of fluid within cavity 24 will always be substantially the same enabling the device to be calibrated. If optional different volumes are required, different rotational positions can be marked on the cap or stops 44 and 46 adapted to be overridden and merely indicate by means of a click each full rotation of the cap to enable one, two, three or four rotations of the cap to be effected (for example), each rotation corresponding to an additional volume of fluid entering the chamber 24.

After the position of maximum displacement has been achieved, cap 18 is screwed down to its original position (as shown in Figure 1) thereby pressurising the trapped fluid in cavity 24. Where the latter is incompressible (as will generally be the case if it is predominently liquid) the downward movement of the cap 18 and inner diaphragm support member 36 will cause diaphragm 20 and its support member 51 to be displaced through a similar distance against the action of the spring 53. The elevated pressure in chamber 24 ensures the central regions 21 and 23 of the two rolling diaphragms 20 and 22 respectively to remain flattened against their respective supports thereby shutting off the reverse flow of fluid through the apertures 54 and 56 and preventing any flow of fluid through any apertures (to be described) in the upper diaphragm 22.

With the charge of fluid in the cavity 24 now pressurised, discharge from the nozzle 27 is obtained by simply permitting the fluid contents of chamber 24 to pass into the spray head 30. This is achieved by depressing spray head 26 relative to the side cheeks 28 of the cap 18 in the direction of arrow 29.

As shown in more detail in Figure 2, albeit inverted, the lower end of member 30 includes a cruciform cross-section abutment 58 which extends through an aperture 60 in the otherwise solid lower end of the member 36. The upper end of the cruciform abutment 58 is secured to or integrally formed with a bridge 62 apertured at 64 and 66. The diaphragm 22 includes apertures 67 and 68 which when the diaphragm is flattened against the underside of the member 36 are effectively closed off so that fluid cannot pass through the diaphragm. In the event that the spray head 26 is depressed, the cruciform abutment 58 presses down on the central region 23 of the diaphragm 22 pushing the latter away from the underside of the member 36 enabling fluid to pass through the apertures 67 and 68 and via the cruciform section into the fluid which passes around the cruciform section of the abutment 58 into the space below the bridge 62. The fluid can pass from there through the apertures 64 and 66 into the member 30 of the spray head 26.

Discharge will continue whilst item 26 is depressed relative to the side cheeks 28 due to the restoring force produced by spring 53 which causes the diaphragm support member 51 and the lower diaphragm 20 to move upwardly until it engages the underside of washer 32. At this point no further discharge will occur.

In order to obtain substantially uniform pressure within cavity 24, the spring 53 is preferably subjected to precompression so that even when support 51 is in its maximum displaced position, the spring is still in compression.

In order to prevent ingress of fluid into the annular space between the upper diaphragm support member 36 and the central housing 30 of the spray head, the periphery of the lower end of item 30 is formed with a sealing skirt 74 (best seen in the inverted view in Figure 2) which sealingly engages against the inside surface of a cylindrical interior of the member 36. Fluid entering the space below the bridge 62 is thus prevented from passing around the skirt into the annular space between 30 and 36 and is consequently forced to enter the member 30 via apertures such as 64 and 66.

The bridge 62 and sealing skirt 74 may be formed integrally from appropriate elastomeric material. Alternatively the seal may be a separate member itself formed typically from elastomeric material secured to and extending radially and axially away from the lower end of the item 30.

After discharge the space 24 can be again filled with fluid by repeating the procedure of rotating the cap 18 so as to displace the upper rolling diaphragm and draw fluid into the space 24 as previously described.

If only partial discharge of the contents of space 24 occurs, so that the lower diaphragm is still displaced from the upper diaphragm and fluid remains therein, the spring 53 maintains pressure in the space 24 and further discharge is available by simply depressing item 26 again.

If partially discharged, chamber 24 is refilled in exactly the same way as previously described except that because of the initial charge of fluid within the chamber 24, the amount of fluid drawn into the chamber is less than would be the case if the chamber 24 were empty to start with, but the final volume of fluid within the chamber remains the same. If metered doses are required (for example for pharmaceutical purposes) the user must be instructed to fully rotate cap 18 to the stop position and then screw the cap back in again so as to ensure that full displacement of the rolling diaphragms is achieved and when discharging the contents of the chamber, the member 26 must be depressed fully and held down until all discharge ceases.

Unlike other metered dose devices, the user can of course interrupt the discharge by simply removing the pressure on the top of item 26 should such an interrupt be desirable.

Alternatively if user interruption is undesirable a latching or servo arrangement may be incorporated to ensure that once the diaphragm 22 has been displaced away from the underside of item 36, and flow has started, diaphragm 22 cannot revert to its original position trapped against the underside of item 36 until the pressure in volume 24 is substantially atmospheric. To this end a floating element having differential areas acted on by fluid above and below the diaphragm may be employed so as to maintain downward displacement of the diaphragm until the pressure in 24 increases again.

This may be achieved by replacing the cricuform plunger 58 with a solid plunger sealingly engaged in the passage in a correspondingly thickened bridge 62, the solid member having a central aperture permitting fluid to communicate through the aperture into the interior of item 30 and having a small cruciform section on its underside or other stand-off means to ensure that fluid can flow between the underside of this member and the upper surface of the diaphragm 22 even when the two are in contact, and the upper end of the member is formed with a very much larger diameter head itself sealingly engaged within the larger diameter interior of item 30. By providing a bleed between the space below the enlarged head and the top surface of the thickened bridge 62, to atmosphere, so the pressure below the enlarged head can never exceed atmospheric and it will be seen that once pressure in item 30 is allowed to increase above atmospheric following displacement of the diaphragm 22 by downward movement of item 26, the member displaceable through the bridge will be bottomed due to the vent to atmosphere against the bridge until such time as the pressure in item 30 is relieved to atmosphere permitting the plunger to rise and allow the rolling diaphra 22 once again to flatten against the underside of item 36.

Figure 3 of the drawings illustrates an alternative arrangement in which the cannister 100 is formed as before with a neck region 102 having a screw thread profile 104 on which is fitted a first part 106 of a two part cap assembly the upper part of which 108 can be rotated relative to the lower part 106 to release a bayonnet or other fixing denoted by reference numeral 110 and enable the part 108 to be lifted relative to the part 106.

Within the upper cap part 108 is a displaceable central member 112 the upper end of which is formed with an exit nozzle 114 through which fluid can pass under pressure.

The inside of the member 112 may include atomising devices or foaming devices or simply comprise passage means to enable fluid to pass therethrough to the exit aperture 114. Member 112 is slidingly received in a central cup 116 located at the lower end of a central cylindrical sleeve 118 the upper end of which merges with and is integrally formed with the remainder of the upper cap portion 108. This sleeve 118 is itself slidingly engaged within an outer tube 120 which is integrally formed at its upper end with the lower cap member 106 secured to the upper end of the cannister 100 and which at its lower end is blocked off either by an integral end or a fitted end plate 122 apertured centrally and formed with a pipe connection 124 onto which a dip tube 126 can be secured.

The tubular member 120 houses the fluid delivery system part of which is in the upper half and part of which is in the lower half of item 120. The two are separated by a cruciform bridge 128 which permits fluid flow from one region to the other of 120 and serves as an end stop for the various items located within 120.

The lower part of the delivery system comprises a free piston 130 which is biased upwardly by a compression spring 132 acting between the end plate 122 and the underside of the piston 130. Above the piston is a cup seal 134 which fits on a central spigot 136 protruding centrally upwardly from the piston 130. The spiggot includes an enlarged head 138 over which the seal can be force fitted but which prevents the seal from thereafter separating from the piston.

The periphery 140 of the cup seal 134 is flexible so that fluid can pass from the cannister 100 through the dip tube 126 and the interior of the lower half of the tube chamber 120 around the piston 130 and past the periphery gap 140 into the space above the seal. Thereafter the fluid can pass through the cruciform bridge 128 (shown in more detail in Figure 4) to the space immediately below the lower end of the sleeve 118. This latter is closed except for apertures denoted by 142 and 144 through which fluid can pass into the space 146 immediately below the lower end of the spray head member 112.

Apertures (not shown) in the lower end of the spray head member 112 permit fluid to enter the same.

With the member 112 in its normally elevated position the apertures are closed off, and even a high fluid pressure in the space 146 will not cause fluid to enter the item 112. However a downwardly protruding cruciform abutment 148 serves as a valve to open the apertures in the event that the member 112 is depressed in the direction of the arrow C and if fluid under pressure exists in the space 146 it will immediately enter the member 112 and appear as a fine mist or foam or gel at the exit nozzle 114 as appropriate.

As shown in Figure 3, both the upper piston assembly formed by member 112 and sleeve 118 and the lower piston assembly 130 and 134 are shown in their home positions and it will be seen that the volume between the two piston assemblies is at a minimum.

Fluid is drawn into this space and the volume increased against the action of the spring 132 by twisting cap 108 and lifting the upper piston assembly. The extent of the lifting is controlled by means of a washer 150 trapped at the upper end of the cannister neck 102 which includes a protruding radial abutment 152 which engages in a slot 154 formed in the wall of the cylindrical sleeve 118. An 0- ring seal 156 prevents a loss of fluid into the region containing the slot and a second O-ring seal 158 seals the lower end of the member 112 within the cup 116.

By lifting cap member 108, the upper piston assembly moves upwards so as to enlarge the volume between it and the upper face of the lip seal 134 causing a drop in pressure in that region. The spigot 138 of the piston 130 prevents the latter from moving upwardly from the position shown but the lip seal is drawn upwardly so that fluid can pass up and around the piston 130 and past the periphery 140 of the cap seal 124 previously described. The fluid flows into the chamber so formed until the pressure is equalised. The charge of fluid is then itself pressurised by pushing down on the cap member 108 and locking the latter using the bayonette fixing 110 into the position shown. Where the fluid trapped between the seal 134 and the lower face of the assembly 118 is incompressible or substantially so, downward movement of the cap member 108 will cause equivalent displacement of the seal and piston 130 against the action of the restoring spring 132, the latter ensuring a good pressure is maintained within the chamber.

The trapped fluid is released as previously described by pressing member 112 so as to open the valve 148 in the lower end thereof to allow fluid to pass into and through the spray cap.

Claims

1. A fluid delivery system comprising:

(a) cannister means

(b) a variable volume reservoir located therein

2. A system according to claim 1, wherein the reservoir is formed between two rolling diaphragms, a lower one of which is acted on by spring means fixedly arranged within the cannister and an upper one of which is movable away from and towards the lower diaphragm by upward and downward movement of a cap displaceably fitted to the upper end of the cannister, and one way valve means is provided for admitting fluid into the reservoir through the lower diaphragm and manually operable valve means is associated with the upper diaphragm to effect exit of fluid from the reservoir through the outlet nozzle.

3. A system according to claim 2, wherein means are provided for normally retaining the cap in its lower position.

4. A system according to claim 3, wherein upward and downward movement of the cap is enabled by screwthreaded engagement of the cap with a sleeve held fixed to the cannister.

5. A system according to claim 2 or claim 3 or claim 4, wherein lifting the displaceable cap, and thereby the upper diaphragm relative to the lower diaphragm, creates a pressure drop within the reservoir between the two diaphragms causing fluid to be sucked into the reservoir with continued upward movement of the cap, and means is provided whereby fluid within the reservoir is prevented from leaving the latter during subsequent downward movement of the cap so that given that the fluid is essentially incompressible, during this downward movement the lower diaphragm is displaced downwardly against the action of the spring means, whereby the latter pressurises the contents of the reservoir to enable operation of the manually operable valve means to force fluid under pressure from the reservoir through the outlet nozzle, whence the discharge of fluid from the reservoir reduces the volume within the reservoir as the lower diaphragm moves upward under the action of the spring until the reservoir has been essentially emptied.

6. A system according to any of claims 2 to 5, wherein the one way valve means comprises apertures in the lower diaphragm cooperating with aperture means at the head of a hollow diaphragm support through which fluid can pass into the reservoir from a main fluid reservoir within the cannister.

7. A system according to any of claims 2 to 6, wherein the manually operable valve means comprises apertures in the upper diaphragm which are normally sealed against the underside of a hollow piston-like member due to the excess pressure within the reservoir, and a peg or plunger which can be manually depressed in a downward direction so as to push the upper diaphragm away from the sealing surface to enable fluid to pass through the apertures into a space communicating with the outlet nozzle.

8. A system according to any of claims 2 to 7, wherein support means is provided at an intermediate position between the two diaphragms, which support means engages at least peripheral regions of the diaphragms when the latter are in their maximum displacement position (downwardly in the case of the upper diaphragm and upwardly in the case of the lower diaphragm) .

9. A system according to any of claims 2 to 8, wherein, since removal of fluid from the cannister tends to create a vacuum, venting means is provided to enable the pressure within the cannister to be balanced to atmospheric pressure.

10. A system according to claim 9, wherein valve means is associated with the vent to enable air to enter the cannister but to prevent fluid from leaving it.

11. A system according to claim 1, wherein the reservoir is formed between a first piston acted on by spring means urging it in an upward sense and a second piston movable both upwardly and downwardly relative to the lower piston by upward and downward movement of a cap associated with the cannister, valve means associated with the first piston permitting fluid to pass from below to above the piston but not in the opposite sense if pressure above the piston exceeds that below the piston, and second valve means openable by manually depressing a release button, permits fluid under pressure to pass from the region between the two pistons through an exit nozzle.

12. A system according to claim 11, wherein means is provided for locking the cap in its lower position.

13. A system according to claim 11 or claim 12, wherein, in operation, when the space between the two pistons is substantially devoid of pressurised fluid, upward movement of the cap and second piston associated therewith causes fluid to be drawn into the space between the two pistons until the cap and said second piston reach a position of maximum upward displacement, whereafter, assuming the fluid is substantially incompressible, downward pressure on the cap forces a charge of fluid and the first mentioned piston in a downward sense as the piston associated with the cap is moved down, thereby compressing a spring means acting on the underside of the first mentioned piston, whereby operation of the second valve means enables fluid under pressure to be discharged through the outlet nozzle, discharge of the fluid from the space between the two pistons causing the spring means to extend and move the lower piston in an upward sense until the lower piston is prevented from moving upwardly any further.

14. A system according to any of claims 11 to 13, wherein venting means is provided to maintain atmospheric pressure within the cannister.

15. A fluid delivery system substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.