Patent Publication Number: US-2009218417-A1

Title: Conformable pouch reservoir for spray gun

Description:
This application is a continuation of U.S. Ser. No. 11/178,779 filed Jul. 11, 2005; which is a divisional of U.S. application Ser. No. 10/430,952 filed May 7, 2003, now U.S. Pat. No. 6,942,126 issued Sep. 13, 2005; which claims priority to United Kingdom Application No. 0210446.1, filed May 8, 2002. 
    
    
     FIELD 
     This invention concerns improvements in or relating to liquid spraying apparatus. The invention is especially concerned with an improved liquid reservoir for use with such liquid spraying apparatus. The invention has particular, but not exclusive, application to pre-packaged liquid reservoirs that can be used with spray guns. 
     BACKGROUND 
     Spray guns are widely used in vehicle body repair shops when re-spraying a vehicle that has been repaired following an accident. In the known spray guns, the liquid is contained in a reservoir attached to the gun from where it is fed to a spray nozzle. On emerging from the spray nozzle, the liquid is atomised and forms a spray with compressed air supplied to the nozzle. The liquid may be gravity fed or, more recently, pressure fed by an air bleed from the compressed air line to the reservoir. 
     One type of known reservoir consists of a rigid pot attached to the spray gun with a removable lid for filling the pot with the liquid to be sprayed onto the substrate. The reservoir is re-usable and both the spray gun and reservoir have to be thoroughly cleaned when changing the liquid in the reservoir to avoid cross-contamination which may adversely affect the finish. This is especially important when spraying part of a vehicle to match exactly the colour of the existing colour of the adjacent bodywork. 
     Cleaning the spray gun and reservoir is time consuming and often requires the use of solvents that are costly and may present a health hazard to the operator. In order to reduce the amount of cleaning and to facilitate changeover from one liquid to another, we have previously proposed in WO 98/32539 a reservoir in which a paint pot is provided with a disposable container received in the pot. The container comprises an open-topped liner that contains the liquid and a separate lid that closes the liner and has an outlet connectable to the spray gun. 
     In use the liner collapses as liquid is withdrawn from the container and, after spraying, the collapsed liner and lid can be removed and thrown away allowing a new, clean liner and lid to be used for applying a different liquid. As a result, the amount of cleaning required is considerably reduced and the spray gun can be readily adapted to apply different liquids in a simple manner. The liner, however, may collapse in a random, uncontrolled manner forming pockets in which liquid can be trapped. This can lead to some of the liquid being thrown away with the collapsed liner and lid which is wasteful. 
     The above-described reservoirs can be used with bulk liquids supplied ready for use such as solvents, lacquers and with liquids that are made-up on demand such as paints requiring matching of the colour to an existing paint finish. Transferring bulk liquids from a storage container is time consuming and can result in spillage which is wasteful and potentially dangerous where the liquid is flammable and/or gives of harmful vapours. Making up liquids on demand is also time consuming and can be wasteful where only a small volume of liquid is required for a given application. 
     SUMMARY 
     The present invention has been made from a consideration of the foregoing disadvantages of known reservoirs for spray guns and seeks to provide an improved reservoir whereby at least some of the disadvantages are avoided or mitigated with resulting benefits and advantages for the manufacturer and/or user. 
     Specifically, in certain embodiments, the present invention provides a reservoir for use with liquid spraying apparatus wherein the reservoir is collapsible in a controlled, reliable manner that permits substantially all of the liquid to be withdrawn from the reservoir. 
     As used herein, the term “liquid” refers to all forms of flowable materials that can be applied using a spray gun (whether or not they are intended to colour the surface) including (without limitation) paints, primers, base coats, lacquers, varnishes and similar paint-like materials as well as other materials such as adhesives, sealers, fillers, putties, powder coatings, blasting powders, abrasive slurries, mould release agents and foundry dressings which may be applied in atomised or non-atomised form depending on the properties and/or the intended application of the material and the term “liquid” is to be construed accordingly. 
     In certain embodiments, the present invention provides a collapsible reservoir that can be supplied pre-filled with liquid for attaching to the liquid spraying apparatus. 
     In certain embodiments, the present invention provides a pre-filled, collapsible reservoir of simple construction whereby manufacture and supply of the reservoir filled with liquid is facilitated. 
     In certain embodiments, the present invention provides a pre-filled, collapsible reservoir which can be stored safely until required. 
     In certain embodiments, the present invention provides a pre-filled, collapsible reservoir which can be fitted to and removed from a spray gun in a reliable manner and can be used to store unused liquid between spraying operations. 
     In certain embodiments, the present invention provides a pre-filled collapsible reservoir that can be thrown away after use. 
     In one aspect, the present invention provides a reservoir for use with liquid spraying apparatus, the reservoir having a substantially rigid first part for releasable connection to liquid spraying apparatus and having an opening through which liquid can be withdrawn for supply to the apparatus, and a flexible second part having an internal surface defining with an internal surface of the first part a chamber containing the liquid wherein the second part is arranged to reduce the volume of the chamber as the liquid is withdrawn from the chamber in use and to conform substantially to the internal surface of the first part in a collapsed condition of the reservoir. 
     By this invention, the reservoir is collapsible in a controlled manner that ensures substantially all the liquid contained in the reservoir can be delivered to the spraying apparatus if required. More particularly, the formation of pockets in which liquid is trapped as the reservoir collapses can be prevented by arranging that the flexible second part conforms substantially to the internal surface of the rigid first part. 
     For convenience, the invention will be described hereinafter with reference to use of the reservoir with a spray gun but it will be understood that the invention is not limited to such use and that the reservoir may be used with other types of liquid spraying apparatus. 
     Preferably, the reservoir is supplied pre-filled with liquid for attachment to the spray gun and, after use, the reservoir can be detached and thrown away. In this way, assembly and filling of the reservoir by the end user may be avoided and the spray gun can be adapted to apply any liquid by fitment of the appropriate reservoir after any necessary cleaning of the spray gun only. As a result, the amount of cleaning required is kept to a minimum and the spray gun can be easily set up to spray different liquids by replacing the reservoir quickly and easily with a minimum disruption. 
     The first and second parts may be formed separately and permanently united during manufacture to form the reservoir. For example, the first and second parts may be secured together by adhesive, heat sealing, ultrasonic welding or other suitable technique. Alternatively, the first and second parts may be formed integrally in one piece. For example, the first and second parts may be formed by injection or blow moulding with the second part being of reduced thickness. 
     Advantageously, the internal surface of the first part extends between an upper, apex end and a lower, base end that is wider than the apex end. The internal surface of the first part may be straight or curved or a combination thereof. For example, the internal surface may be of conical or part spherical shape. Preferably, the opening is at the upper, apex end for connecting the reservoir to the spray gun, and the flexible second part is at the lower, base end opposite the opening. 
     Preferably, the first part comprises a substantially rigid body and the flexible second part comprises a diaphragm arranged to deform into the body in response to withdrawal of liquid from the reservoir and conform substantially to the internal surface eof the body in the collapsed condition. The body and/or diaphragm may be adapted to provide the reservoir with additional desirable properties or characteristics in use. For example, the reservoir may be adapted to exclude light or provide insulation. 
     In one arrangement, the second part comprises an elastic diaphragm of extensible material arranged to extend in a substantially flat condition across the lower, base end of the first part when the reservoir is filled with liquid. Suitable materials include elastomers such as rubber. 
     With this arrangement, the reservoir can stand in an upright position supported by the base end of the first part with the diaphragm concealed and protected by the first part when the reservoir is not in use. The wider, base end of the first part provides stability against tipping in the upright position and the diaphragm does not affect stability of the reservoir in this condition. As a result, the risk of accidental or inadvertent puncturing of the diaphragm is reduced when the reservoir is not in use. 
     In use, the diaphragm stretches and deforms inwardly towards the opening to reduce the volume of the chamber when liquid is withdrawn from the reservoir. In this way, the diaphragm progressively engages the internal surface from the wider base end towards the apex end until, in the fully collapsed condition of the reservoir, the diaphragm conforms to the shape of the internal surface of the first part. This prevents pockets being formed between the diaphragm and the internal surface in which liquid may be trapped. As a result, substantially all the liquid can be discharged in the fully collapsed condition of the reservoir. 
     In another arrangement, the second part comprises a reversible diaphragm of substantially inextensible material. Suitable materials include metal foils or polymer films or similar flexible sheet materials of single or multi-layer construction including laminates of one or more of these materials that are preferably puncture resistant and impermeable to the liquid contained in the reservoir. 
     Preferably, the diaphragm is of substantially the same shape as the internal surface of the first part. With this arrangement, the diaphragm extends away from the base end of the first part and is a mirror image of the internal surface of the first part when the reservoir is filled with liquid. As a result, for a first part of the same size and shape, the volume of the reservoir is approximately doubled compared to the previous arrangement. The apex end of the diaphragm may be flattened so that the reservoir can stand in an upright position when filled with liquid. 
     In use the diaphragm deforms inwardly to reduce the volume of the chamber as liquid is withdrawn from the reservoir. In this way, the diaphragm progressively engages the internal surface of the first part from the wider base end towards the apex end. In the fully collapsed condition of the reservoir, the diaphragm is reversed from its initial position and conforms substantially to the shape of the internal surface of the first part. This prevents pockets being formed between the diaphragm and the internal surface in which liquid may be trapped. As a result, substantially all the liquid can be discharged in the fully collapsed condition of the reservoir. 
     In both arrangements, the first part is preferably adapted to prevent the opening being completely closed-off by the diaphragm when liquid is withdrawn from the reservoir. For example, the first part may provide a path that allows the last of the liquid to be dispensed as the diaphragm collapses inwardly. In this way, substantially complete dispense of the liquid is assured. For example, the first part may be provided with one or more formations at the marginal edge of the opening to provide at least one aperture that remains open in the fully collapsed condition of the reservoir. The path may extend from the marginal edge of the opening towards the base end of the first part. For example, the internal surface of the first part may be provided with one or more raised ribs or recessed channels. 
     Advantageously, the opening in the first part is provided with a spout for connecting the reservoir to the spray gun in a fluid tight manner. For example, the reservoir may be detachably secured to an adapter attached to the spray gun. The reservoir and adapter may be provided with co-operating formations for releasably securing the reservoir. The formations may be engageable with a push/twist action to lock the reservoir in position. The formations may be released by a reverse action or by pulling the reservoir away from the spray gun. In this way, the reservoir can be connected to and released from the spray gun with a simple action requiring minimum effort and/or manual dexterity by the user. 
     Preferably, the first part has a size and shape that can be held by the user to attach and detach the reservoir without compressing the liquid in the reservoir. As a result, the integrity of the reservoir is not compromised when fitting the reservoir and the risk of spillage when removing the reservoir is reduced. 
     The reservoir may be filled with liquid introduced through the spout and the spout closed to seal the reservoir until the reservoir is to be fitted to the spray gun. For example, the spout may be closed by a rupturable membrane such as a foil cap. The user may pierce the membrane prior to attaching the reservoir to the spray gun. Alternatively, the membrane may be ruptured automatically when the reservoir is attached to the spray gun. 
     Preferably, the spout is provided with a separate detachable cap to protect the membrane from accidental or inadvertent rupturing prior to fitting the reservoir to the spray gun. The cap may be re-fitted to seal the spout when the reservoir is detached from the spray gun to prevent spillage or leakage of any liquid remaining in the reservoir. The reservoir may then be thrown away in a sealed condition for safe disposal of the contents or stored for later re-attachment to the spray gun to use the remaining liquid. 
     Alternatively, the spout may be provided with a manually operable valve to open and close the opening. The valve may be operable with the reservoir secured to the spray gun. In this way, the reservoir may be attached to the spray gun with the opening closed and the valve actuated to open the outlet and permit transfer of liquid to the spray gun. Similarly, when it is desired to remove the reservoir, the valve may be actuated to close the opening before detaching the reservoir. In this way, the risk of spillage or leakage of the contents of the reservoir is reduced. Moreover, any unused liquid can be stored in the reservoir for later use by re-attaching the reservoir to the spray gun. The provision of a valve forms the subject matter of our co-pending UK patent application of even date. 
     A filter may be provided to remove any unwanted solid particles from liquid withdrawn from the reservoir to the spray gun in use. For example, the filter may comprise a removable mesh screen fitted in the spout after filling the reservoir with the liquid and before closing the spout. 
     According to a second aspect of the present invention, there is provided liquid spraying apparatus in combination with a reservoir according to the first aspect of the invention. 
     The liquid spraying apparatus may be a spray gun. The spray gun may be of the gravity fed type in which a pressure differential is created across the flexible member as liquid is withdrawn from the reservoir causing the member to deform inwardly towards the opening. Alternatively, the spray gun may be of the pressure fed type in which the reservoir is arranged so that the flexible member is exposed to an increased air pressure externally of the reservoir by an air bleed from the compressed air supply line to the gun. 
     Other features, benefits and advantages of the invention will be understood from the following description of exemplary embodiments with reference to the accompanying drawings in which like reference numerals are used throughout to indicate corresponding parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art spray gun; 
         FIG. 2  is an exploded isometric view of the component parts of the paint reservoir shown in  FIG. 1 ; 
         FIG. 3  is a perspective view showing the paint reservoir of  FIG. 2  assembled and an adapter for connecting the reservoir to the spray gun; 
         FIG. 4  is a longitudinal section through the paint reservoir and adapter shown in  FIG. 3 ; 
         FIG. 5  is a side view of a first embodiment of a paint reservoir for use with a spray gun according to the present invention, the reservoir being shown in its pre-filled condition for fitment to the spray gun; 
         FIG. 6  is a diagrammatic side view, similar to  FIG. 5 , showing the change in shape of the reservoir as the contents are discharged; 
         FIG. 7  is a perspective view showing the reservoir of  FIGS. 5 and 6  attached to the spray gun of  FIG. 1 ; 
         FIG. 8  shows a modification to the reservoir of  FIGS. 5 to 7 ; 
         FIG. 9  shows another modification to the reservoir of  FIGS. 5 to 7 ; 
         FIG. 10  shows yet another modification to the reservoir of  FIGS. 5 to 7 ; 
         FIG. 11  is a longitudinal section of a second embodiment of a paint reservoir according to the present invention, the reservoir being shown in its pre-filled condition for attachment to the spray gun; 
         FIG. 12  is a longitudinal section similar to  FIG. 11  showing the reservoir in its collapsed condition; 
         FIG. 13  shows a modification to the reservoir of  FIG. 11 ; 
         FIG. 14  shows another modification to the reservoir of  FIG. 11 ; 
         FIG. 15  shows yet another modification to the reservoir of  FIG. 11 ; 
         FIG. 16  shows a still further modification to the reservoir of  FIG. 11  to provide the spout with a valve device, the valve device being shown closed; 
         FIG. 17  is a view similar to  FIG. 16  showing the valve device open; 
         FIG. 18  is a longitudinal section through the reservoir shown in  FIGS. 16 and 17  with the outer sleeve of the valve device removed; 
         FIG. 19  is a longitudinal section through the outer sleeve of the valve device shown in  FIGS. 16 and 17 ; 
         FIG. 20  is a perspective view of an adapter for connecting the reservoir of  FIG. 16  to a spray gun; 
         FIG. 21  is a plan view of the adapter shown in  FIG. 20 ; and 
         FIGS. 22 to 24  are schematic views of formations to keep the outlet from the reservoir open in the collapsed condition. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  of the drawings illustrates a prior art paint spray gun  1  of the gravity-feed type disclosed in our co-pending patent application published under No: WO 98/32539 the contents of which are incorporated herein by reference. 
     The gun  1  comprises a body  2 , a handle  3  which extends downwards from the rear end of the body, and a spray nozzle  4  at the front end of the body. The gun  1  is manually-operated by a trigger  5  which is pivotally-mounted on the sides of the gun. 
     A paint pot  6 , which contains paint (or similar material) to be discharged by the gun, is located on the top of the body  2  and communicates with an internal passageway (not visible) which extends through the gun to the nozzle  4 . 
     In use, the gun  1  is connected via a connector  7  at the lower end of the handle  3  to a source of compressed air (not shown) so that, when the user pulls on the trigger  5 , compressed air is delivered through the gun to the nozzle  4 . As a result, paint delivered under gravity from the pot  6  to the nozzle  4  is atomised on leaving the nozzle  4  and forms a spray with the compressed air emerging from the nozzle  4 . 
     Referring now to  FIGS. 2 to 4  of the drawings, the paint pot  6  includes an outer container  8 , a disposable liner  9 , a disposable lid  10  and a collar  11 . The liner  9  corresponds in shape to (and is a close fit in) the interior of the container  8  and has a narrow rim  12  at the open end which sits on the top edge of the container  8 . 
     The lid  10  has a dependent skirt  13  at the peripheral edge which is a push-fit in the open end of the liner  9  and a central aperture  14  from which extends a connector tube  15  forming a fluid outlet. The tube  15  is provided at its free end with outward extensions  16  forming one part of a bayonet connection. The aperture  14  is covered by a filter mesh  17  which may be a push fit into the aperture  14  or may be an integral part of the lid  10 . 
     The lid  10  is held firmly in place on the container  8  by the annular collar  11  that screws onto the container  8  on top of the lid  10 . In the assembled condition, the liner  9  and lid  10  form a reservoir for containing the paint or other liquid to be delivered to the nozzle  4  via the connector tube  15 . 
     The paint pot  6  is attached to the spray gun  1  through use of an adapter  18  which is formed internally at one end  19  with the other part of the bayonet connection for attachment to the connector tube  15  of the lid  10 . At the other end  20 , the adapter  18  is shaped to match the standard attachment of the spray gun paint pot (typically a screw thread). 
     To use the paint pot  6 , the adapter  18  is attached at the end  20  to the spray gun and is left in position. Then, with the paint pot  6  disassembled as shown in  FIG. 2 , the liner  9  is pushed inside the container  8 . Paint is then put into the liner  9  and, if necessary, mixed with other tinters, hardeners and thinners (solvents). The lid  10  is then pushed into place and the collar  11  is screwed down tightly to hold the lid  10  in position. 
     The spray gun  1  is then inverted from its normal operating position illustrated in  FIG. 1  so that the paint pot  6  can be presented to the spray gun  1  in an upright position to prevent spillage of paint. The end of the connector tube  15  is then attached to the adapter  18  to secure releasably the paint pot  6  to the spray gun  1 . The spray gun  1  can then be returned to its normal operating position for use in the usual way. 
     In use, as paint is withdrawn from the reservoir, the liner  9  collapses in an axial direction from base end  9 A towards the lid  10 . A vent hole  8 A in the base end of the container  8  allows air to enter the container  8  as the liner  9  collapses. Sidewall  9 B of the liner  9  folds inwardly in a random, uncontrolled manner as the liner  9  collapses. This can result in pockets being formed that trap and retain paint within the liner  9  and prevent all of the paint being transferred to the spray gun  1 . 
     After use, when the spray gun  1  is to be cleaned, the spray gun  1  can be re-inverted from its operating position shown in  FIG. 1 , the airline disconnected and the trigger  5  actuated briefly to allow paint within the spray gun  1  to drain back into the liner  9  in the pot  6 . The pot  6  is then removed from the spray gun  1  by detaching the connector tube  15  from the adapter  18  which remains on the spray gun  1 . 
     The collar  11  is removed from the container  8 , and the lid  10  is then pulled out, bringing with it the collapsed liner  9 , leaving the container  8  and collar  11  clean and ready for re-use with a fresh liner  9  and lid  10 . Only the spray gun  1  itself needs to be cleaned, resulting in a substantial reduction in the amount of solvent used. 
     Any paint remaining in the liner  9  may be stored for a short period of time by sealing the connector tube  15 , for example with a detachable closure cap (not shown). The lid/liner assembly can then be re-assembled with the container  8  and collar  11  and re-attached to the spray gun  1  to use the remaining paint. 
     When removed from the container  8 , the lid/liner assembly is relatively fragile and susceptible to separation of the liner  9  and lid  10  if mishandled. Accordingly, it is generally only practical to store unused paint for a few hours and any unused paint must be decanted into another container if long term storage is required. When all the paint has been used or if any remaining paint is no longer required, the lid  10  (including the filter  17 ) and collapsed liner  9  can be discarded. 
     The arrangement of the disposable liner  9  and separate, disposable lid  10  to form a reservoir to contain the paint or other liquid to be sprayed considerably reduces the amount of cleaning required when changing the liquid to be sprayed or when putting the spray gun  1  away at the end of the working day. This is a considerable improvement over arrangements where both the spray gun and the reservoir have to be cleaned and provides many benefits for the user. 
     It will be apparent, however, that assembly of the reservoir and its fitment to and removal from the spray gun can be time consuming to ensure the various components are correctly assembled for proper functioning and to reduce the risk of leakage. 
     Referring now to  FIGS. 5 to 7  of the drawings, there is shown a first embodiment of a disposable, pre-filled reservoir according to the present invention that can be fitted to the spray gun in a simple manner. The reservoir is particularly suitable for manufacture and supply of a liquid that does not require accurate matching of the colour such as primers, lacquers, solvents. 
     As shown, the reservoir  51  has a rigid body  52  of conical shape closed at the wider base end by an extensible, flexible diaphragm  53  that defines with the body  52  a chamber  54 . The body  52  is provided with an opening  55  at the apex end opposite the diaphragm  53  that leads to a spout  56  formed integrally with the body  52 . 
     The body  52  and diaphragm  53  are made of materials compatible with the liquid  57  contained in the reservoir  51 . In this embodiment, the body  52  is made of a plastic material such as polyethylene terepthalate (PET) or polyamide by injection moulding. The diaphragm  53  is made of an elastic material such as rubber or similar elastomer bonded to the body  52  by any suitable method, for example adhesive, heat sealing or ultrasonic welding. 
     The reservoir  51  may be opaque if the liquid  57  is light sensitive. Alternatively, if the liquid  57  is light stable, the body  52  may be transparent or translucent to allow visual inspection of the liquid  57  in the reservoir  51 . The body  52  may also be provided with scale markings to indicate the volume of liquid  57  in the reservoir  51 . 
     The reservoir  51  is pre-filled with liquid  57  introduced through the spout  56  and the spout  56  closed to seal the reservoir  51  by attaching a rupturable membrane such as a foil cap (not shown) across the outer end. Alternatively, the spout may be closed by any other suitable means such as a screw cap, bung or ring pull. A filter (not shown) may be located in the spout  56  after filling the reservoir  51  to remove any solid particles when the liquid  57  is dispensed in use of the reservoir  51 . 
     The volume of the reservoir  51  is determined by the dimensions of the body  52  using the formula V=⅓Πr 2 h where r is the radius of the base end of the body  52  and h is the height of the body  52 . For example, a radius of 5 cm and a height of 2.5 cm produces a volume of 65 cc. As will be appreciated, the reservoir  51  can be constructed to provide any desired volume by altering the dimensions of the body  52 . 
     Thus, the body  52  may be constructed to provide a reservoir  51  capable of holding sufficient liquid  57  for a single application or for multiple applications. The reservoir  51  may be substantially completely filled with the liquid  57  or slightly underfilled to allow the liquid  57  to be thoroughly mixed prior to use by shaking the reservoir  51  by hand or machine, possibly aided by an internal mixing bearing. This may be advantageous and/or desirable where the reservoir  51  has been stored for some time before use. 
     The diaphragm  53  forms a substantially flat base when the reservoir  51  is filled with the liquid  57 . In this way, the reservoir  51  is free-standing and can be stood upright on the base supported by the wider base end of the rigid body  52 . This provides a particularly stable arrangement for supply and storage of the pre-filled reservoir  51  and reduces the risk of accidental or inadvertent puncturing of the diaphragm  53 . 
     The spout  56  is provided with bayonet formations (not shown) compatible with the bayonet formations of the adapter  18  ( FIGS. 3 and 4 ) by means of which the reservoir  51  can be releasably connected to the spray gun  1  ( FIG. 1 ) as described previously. It will be understood, however, that any other suitable method of releasably connecting the reservoir  51  may be employed, for example screw fit, compression fit or locking collar. 
     Prior to attaching the reservoir  51 , the rupturable membrane closing the spout  56  is pierced or removed. Alternatively, the membrane may be pierced automatically when the reservoir  51  is connected to the spray gun  1 . 
     The rigid body  52  is of size and shape that the user can grip the base end both when attaching the reservoir  51  to and when detaching the reservoir  51  from the spray gun  1 . In this way, the liquid  57  in the reservoir  51  is not compressed when attaching/detaching the reservoir  51  thereby reducing the risk of leaks/spillage. 
     In use of the spray gun  1 , as the liquid  57  is withdrawn from the reservoir  51  via the spout  56 , a pressure differential is created across the diaphragm  53  causing it to stretch and deform inwardly towards the spout  56  as shown in  FIG. 6 . This allows a smooth uninterrupted flow of liquid  57  from the reservoir  51  by preventing formation of a vacuum within the reservoir  51 . In addition, the diaphragm  53  is sufficiently elastic to stretch and progressively engage the internal surface of the rigid body  52  in a controlled manner as the liquid  57  is being withdrawn. 
     In the fully collapsed condition shown in dotted outline in  FIG. 6 , the diaphragm  53  conforms substantially to the internal shape of the rigid body  52 . This assists in preventing formation of any pockets within the reservoir  51  that could trap the liquid  57  thereby ensuring substantially all the liquid  57  can be dispensed if required. Afterwards, the diaphragm  53  can return to its original shape when spraying is stopped. 
     In a modification, the body  52  may be adapted to prevent the opening  55  being closed-off by the diaphragm  53  when liquid is withdrawn from the reservoir  51  so that the last of the liquid can be dispensed. For example, as shown in  FIGS. 22 and 23 , the body  52  may be provided with protruding ribs  75  radially disposed around the opening  55  and additional protruding ribs  76  disposed between and radially outwardly of the ribs  75 . The ribs  75 ,  76  provide flow channels for liquid to flow to the opening  55  from anywhere in the reservoir  51 . In this way, the ribs  75 ,  76  allow the last of the liquid to be dispensed and prevent the opening  55  being closed-off as the diaphragm  53  collapses inwardly towards the opening  55 . The number, shape and position of the ribs  75 ,  76  may be altered from that shown to provide any desired flow channels for the liquid to reach the opening  55 . 
     Alternatively, as shown in  FIG. 24 , the body  52  may be provided with a spiral flow channel  77  extending from the wider base end to the opening  55 . In this way, the channel  77  provides a path for the last of the liquid to be dispensed and prevents the opening  55  being closed-off as the diaphragm  53  collapses inwardly towards the opening  55 . The shape and position of the channel  77  may be varied and more than one channel  77  may be provided to allow the liquid to reach the opening  55  from any part of the reservoir  51 . 
     It will be understood, that any other suitable arrangement may be provided to ensure that a path is kept open for the last of the liquid to be dispensed. 
     A detachable closure cap (not shown) may be provided for securing to the spout  56  to prevent accidental or inadvertent piercing of the rupturable membrane before use of the reservoir  51  and/or to allow the reservoir  51  to be re-sealed if removed from the spray gun  1  before all of the liquid  57  has been dispensed. In this way, any unused liquid can be stored in the reservoir  51  and the reservoir  51  later re-attached to the spray gun  1  for further use. The unitary construction of the reservoir  51  with the diaphragm  53  bonded to the body  52  is robust and permits long term storage of the unused paint in the reservoir  51  without risk of spillage or leakage. 
     Various modifications to the reservoir  51  above-described are shown in  FIGS. 8 to 10  in which like reference numerals are used to indicate corresponding parts. 
     In  FIG. 8 , an alternative shape of reservoir  51  is shown in which the rigid body  52  has a conical upper portion  52   a  and a cylindrical lower portion  52   b  with the diaphragm  53  secured to the base end of the lower portion  52   b . This shape of body  52  is again free-standing and enables the volume of the reservoir  51  to be increased without increasing the radius of the conical portion  52   a  while still allowing the diaphragm  53  to deflect into the body  52  as liquid is withdrawn from the reservoir  51 . This may be desirable where a conical portion of much larger radius could make the spray gun  1  unstable and difficult to use. Other shapes of reservoir that could be employed with a free-standing body  52  and diaphragm  53  will be apparent to those skilled in the art. 
     In  FIG. 9 , the reservoir  51  is shown with a plug  60  of self-sealing elastomeric material in the wall of the rigid body  52 . The plug  60  allows addition of a liquid to the liquid  57  in the reservoir  51  by means of a syringe. This may be desirable where the two liquids have to be mixed immediately prior to use, for example the addition of hardeners or activators to a base liquid. Alternatively, the added liquid may be employed to modify the characteristics of a base liquid in the reservoir, for example the addition of tinters to alter the colour (shade) of a base coat or thinners (solvent) to alter the viscosity of a finishing clearcoat such as lacquer for “fading out” or “blending”. 
     In  FIG. 10 , the reservoir  51  is shown with an internal shoulder  70  leading to an annular rim  71  at the base end. The diaphragm  53  is secured to the shoulder  70  and the rim  71  provides a support base for the reservoir  51 . The rim  71  may be continuous or a series of discrete projections spaced apart around the base end. In this way, the reservoir  51  can be stood upright on a surface with the diaphragm  53  spaced above the surface to improve stability of the reservoir  51  and reduce further the risk of accidental or inadvertent puncturing of the diaphragm  53 . 
     In a further modification, not shown, we may provide a base cap that fits over the base end of the reservoir  51  to protect the diaphragm  53  when the reservoir  51  is not in use. The base cap may be removable when the reservoir  51  is attached to the spray gun  1  to expose the diaphragm  53  to atmospheric pressure externally of the reservoir  51 . Alternatively, the base cap may be provided with at least one hole to expose the diaphragm  53  to atmospheric pressure. In a still further modification (not shown) for use of the reservoir with a pressure fed spray gun, the hole may allow attachment of an air bleed from the compressed air supply line to the spray gun to expose the diaphragm to a positive pressure higher than atmospheric pressure. 
     Referring now to  FIGS. 11 and 12  of the drawings, there is shown a second embodiment of a disposable, pre-filled reservoir according to the present invention that can be fitted to the spray gun in a simple manner. Similar to the previous embodiment, this reservoir is particularly suitable for manufacture and supply of a liquid that does not require accurate matching of the colour such as primers, lacquers, solvents. For convenience, like reference numerals in the series  100  are used to indicate parts of the second embodiment corresponding to the first embodiment. 
     The reservoir  151  is shown in its extended or filled condition in  FIG. 11  and in its collapsed or empty condition in  FIG. 12 . The reservoir  151  has a rigid body  152  of conical shape and an inextensible, flexible diaphragm  153  also of conical shape that define a chamber  154 . 
     The body  152  is provided with an opening  155  at the apex end that leads to a spout  156  formed integrally with the body  152 . The reservoir  151  may be opaque if the liquid  157  contained therein is light sensitive. Alternatively, if the liquid  157  is light stable, the body  152  and/or diaphragm  153  may be transparent or translucent to allow visual inspection of the liquid  157  in the reservoir  151 . The reservoir  151  may also be provided with scale markings to indicate the volume of liquid  157  in the reservoir  151 . 
     The body  152  and diaphragm  153  are made of materials compatible with the liquid  157  contained in the reservoir  151 . In this embodiment, the body  152  is made of a plastic material such as polyethylene terepthalate (PET) or polyamide by injection moulding. The diaphragm  153  is made of an inelastic material and may be formed separately from the body  152  and bonded to the body  152  by any suitable method, for example adhesive, heat sealing or ultrasonic welding. Suitable materials for this can include metal foils and polymer films which may be of single or multi-layer construction and may include laminates of metal foils and polymer films. Alternatively, the diaphragm  153  may be formed integrally with the body  152 . Suitable materials for this include plastics which may be the same or different to the plastic material of the body  152 . 
     The reservoir  151  is pre-filled with liquid  157  introduced through the spout  156  and the spout  156  closed to seal the reservoir  151  by attaching a rupturable membrane such as a foil strip (not shown) across the outer end. A filter (not shown) may be employed to remove any solid particles from the liquid  157  during filling. Alternatively or additionally, a filter (not shown) may be located in the spout  156  after filling the reservoir  151  to remove any solid particles when the liquid  157  is dispensed in use of the reservoir  151 . 
     The conical shape of the diaphragm  153  generally corresponds to the internal conical shape of the body  152 . As shown, the apex end of the body  152  is truncated where the spout  156  is connected. The diaphragm  153  has a similar truncated apex end that forms a substantially flat surface  158  by means of which the reservoir  151  can be stood upright when filled with liquid  157  if desired. 
     In the extended position shown in  FIG. 11 , the internal surface of the chamber  154  is approximately symmetrical about a centre line CL where the base end of the body  152  is joined to the base end of the diaphragm  153 . In this way, for a given height and radius of the body  152 , the volume of the chamber  154  is substantially doubled compared to the first embodiment shown in  FIGS. 5 to 7 . 
     The reservoir  151  may hold sufficient liquid  157  for a single application or for multiple applications. The reservoir  151  may be substantially completely filled with the liquid  157  or slightly underfilled to allow the liquid  157  to be thoroughly mixed prior to use by massaging the diaphragm  153  or by shaking the reservoir  151  by hand or machine, possibly aided by an internal mixing bearing. This may be advantageous and/or desirable where the reservoir  151  has been stored for some time before use. 
     The spout  156  is provided with bayonet formations (not shown) compatible with the bayonet formations of the adapter  18  ( FIGS. 3 and 4 ) by means of which the reservoir  151  can be connected to the spray gun  1  ( FIG. 1 ). Prior to attaching the reservoir  151 , the rupturable membrane closing the spout  156  is pierced or removed. Alternatively, the membrane may be pierced automatically when the reservoir  151  is connected to the spray gun  1 . The rigid body  152  is again of a size and shape that the user can grip the base end both when attaching the reservoir  151  to and when detaching the reservoir  151  from the spray gun  1 . In this way, the liquid  157  in the reservoir  151  is not compressed when attaching/detaching the reservoir  151  thereby reducing the risk of leaks/spillage. 
     In use of the spray gun  1 , as the liquid  157  is withdrawn from the reservoir  151  via the spout  156 , a pressure differential is created across the diaphragm  153  causing it to deform inwardly towards the spout  156  as shown in outline in  FIG. 12 . This allows a smooth uninterrupted flow of liquid  157  from the reservoir  151  by preventing formation of a vacuum within the reservoir  151 . In addition, the diaphragm  153  is sufficiently pliable to progressively engage the internal surface of the rigid body  152  as the liquid  157  is being withdrawn. In the fully collapsed condition shown in  FIG. 12 , the diaphragm  153  is reversed from its original position and conforms substantially to the internal shape of the rigid body  152 . This assists in preventing formation of any pockets within the reservoir  151  that could trap the liquid  157  thereby ensuring substantially all the liquid  157  can be dispensed if required. The body  152  may be adapted as described previously to provide a path that prevents the opening  155  being completely closed-off and allow the last of the liquid to be dispensed as the diaphragm  153  collapses. 
     A detachable closure cap (not shown) may be provided for securing to the spout  156  to prevent accidental or inadvertent piercing of the rupturable membrane before use of the reservoir  151 . Alternatively or additionally, the closure cap may allow the reservoir  151  to be re-sealed if removed from the spray gun  1  before all of the liquid  157  has been dispensed. In this way, any unused liquid can be stored in the reservoir  151  and the reservoir  151  later re-attached to the spray gun  1  for further use. Again the unitary construction of the reservoir  151  facilitates long term storage of any unused paint in a safe manner. 
     Various modifications to the shape of reservoir  151  above-described are shown in  FIGS. 13 to 15  in which like reference numerals are used to indicate corresponding parts. 
     In  FIG. 13 , the internal surface of the rigid body  152  and reversible diaphragm  153  are of truncated tetrahedral shape. Other truncated shapes with multiple flat sides such as pyramidal may be employed. 
     In  FIG. 14 , the internal surface of the rigid body  152  and reversible diaphragm  153  are of hemispherical shape. The hemispherical shape can usefully be employed to increase significantly the volume of the reservoir  151  for a given radius compared to the conical shape of  FIG. 11 . The diaphragm  153  may be provided with a flat base surface for standing the reservoir  151  upright if desired. 
     In  FIG. 15 , the internal surface of the rigid body  152  is of truncated conical shape and the reversible diaphragm  153  is of hemispherical shape. The hemispherical shape of the diaphragm  153  increases the volume of the reservoir  151  and is sufficiently similar to the internal shape of the rigid body  152  to allow the diaphragm  153  to conform to the internal surface of the rigid body  152  in the collapsed condition. 
     Other shapes that could be employed whereby the diaphragm  153  conforms substantially to the internal shape of the rigid body  152  in the collapsed condition will be apparent to those skilled in the art. 
     With reference now to  FIGS. 16 to 19  of the drawings, a third embodiment of a collapsible, pre-filled reservoir according to the present invention is shown in which a valve device is provided for controlling flow of paint from the reservoir. The construction and operation of the reservoir is similar to the second embodiment and will be understood from the description of the second embodiment. For convenience like reference numerals in the series  200  are used to indicate parts of the third embodiment corresponding to the second embodiment 
     In this embodiment, the spout  256  is provided with a valve device  280  for controlling flow of paint from the reservoir  251 . The valve device  280  is shown closed in  FIG. 16  to seal the reservoir  251  and open in  FIG. 17  to allow paint to be withdrawn from the reservoir  251 . 
     The spout  256  is formed at the outer end with a series of circumferentially spaced internal webs or spurs  281  that meet at a central plug  282 . The plug  282  is cylindrical and projects above the horizontal plane through from the end of the spout  256 . In this embodiment, there are six webs  281  (two only shown) uniformly spaced in the circumferential direction and defining with the plug  282  six ports  305  through which paint can flow in the open condition of the valve device  280 . 
     The valve device  280  includes an outer sleeve  283  slidably mounted on the spout  256 . The sleeve  283  has an internal wall  284  at the upper end formed with a central opening  285  aligned with the plug  282 . The plug  282  is a close fit in the opening  285  in the closed condition of the valve device  280  shown in  FIG. 16  in which the wall  284  closes the ports  305  between the plug  282  and webs  281 . In this position, the wall  284  prevents flow of paint from the reservoir  251 . 
     The sleeve  283  is axially slidable on the spout  256  to a position in which the central opening  285  of the wall  284  is clear of the plug  282  as shown in  FIG. 17 . In this position, the valve device  280  is open and paint can flow out of the reservoir  251  via the ports and central opening  285 . 
     The sleeve  283  is prevented from rotating on the spout  256  by engagement of two diametrically opposed axially extending ribs  286  on the outer surface of the spout  256  in complementary axially aligned grooves (not shown) in the inner surface of the sleeve  283 . 
     The ribs  286  extend from the base of the spout  256  just over half the height and the spout  256  is provided with an external annular lip  287  adjacent the upper end. The grooves extend from the base of the sleeve  283  just over half the height and terminate in an internal shoulder  288  leading to a bore portion  289  of increased diameter. 
     The annular lip  287  on the spout  256  is a clearance fit in the bore portion  289  and the shoulder  288  is engageable with the lip  287  in the open condition of the valve device  280  shown in  FIG. 17  to retain the sleeve  283  on the spout  256 . In the closed condition of the valve device  280  shown in  FIG. 16 , the end wall  284  of the sleeve  283  abuts the outer end of the spout  256 . 
     The sleeve  283  is additionally provided at the lower end with a pair of diametrically opposed arms  290  that extend downwardly, generally parallel to the body  252 , and terminate at the outer ends in upwardly curved finger grips or pulls  291 . 
     Each arm  290  is provided with an upstanding retainer hook  292  spaced from the sleeve  283  and terminating at the upper end in a striker head  293  having a chamfer face  294  opposite the sleeve  283  leading to an undercut locking rib  295 . 
     The sleeve  283  is a push fit in one end of an adapter  296  (see  FIGS. 20 and 21 ) and has an external annular rib  297  providing a fluid-tight seal with the adapter  296 . The other end of the adapter  296  is provided with an internal screw thread  298  or other suitable means for releasable connection to the spray gun  1  ( FIG. 1 ). 
     The adapter  296  has a through bore  299  for transferring paint from the reservoir  251  to the spray gun  1  and is provided with an external collar  300  at one end for releasable engagement with the retainer hooks  292  to secure the reservoir  251 . 
     As best shown in  FIG. 21 , the collar  300  has major cylindrically concave recesses  301  along opposite sides of its periphery arranged to allow the striker heads  293  of the retainer hooks  292  to pass when the sleeve  283  is pushed into the end of the adapter  296 . The reservoir  251  can then be rotated relative to the adapter  296  to cause the retainer hooks  292  to engage convex cam lobes  302  that deflect the hooks  292  outwardly. The lobes  302  lead to minor cylindrically concave recesses  303  and the hooks  292  are received in the recesses  303  to position the locking ribs  295  over a surface  304  of the collar  300  to axially retain the reservoir  251  on the adapter  296 . 
     The retainer hooks  292  can be released to remove the reservoir  251  from the adapter  296  by manually gripping the finger grips  291  and pulling the arms  290  towards the body  252 . This causes the retainer hooks  292  to deflect outwardly so as to disengage the locking ribs  295  from the surface  304  of the adapter  296  and allow the sleeve  283  to be pulled out of the adapter  296  to detach the reservoir  251 . 
     In use, the adapter  296  is secured to the spray gun  1  and the pre-filled reservoir  251  attached with the valve  280  closed by pushing the sleeve  283  into the end of the adapter  296  and rotating the reservoir  251  to engage the locking ribs  295 . The reservoir  251  can be inverted with the valve  280  closed for attaching to the spray gun  1  with the spray gun  1  in its normal, upright position of use without any risk of spillage of paint from the reservoir  251 . 
     In this way, the spray gun  1  does not have to be inverted when connecting the reservoir  251  to the spray gun  1  thereby facilitating attaching the reservoir  251  to the spray gun  1 . In particular, it will be appreciated that less manual dexterity is required when fitting the reservoir  251  from above the spray gun  1  compared to arrangements in which the spray gun  1  must be inverted and the reservoir connected from below to prevent spillage of the paint from the reservoir. 
     As will be appreciated, the action of pushing and rotating to lock the reservoir  251  to the adapter  296  maintains the valve device  280  in the closed position shown in  FIG. 16 . When it is desired to commence spraying, the spout  256  is displaced axially relative to the sleeve  283  by pulling the body  252  away from the spray gun  1  to move the valve device  280  to the open position shown in  FIG. 17 . The spray gun  1  can then be operated as described previously and paint is delivered to the spray gun  1  through the open ports in the spout  256  and the opening  285  in the end wall  284  of the sleeve  283 . 
     On completion of spraying, spray gun  1  can be inverted to allow paint to drain back into the reservoir  251 . The valve device  280  can then be returned to the closed position shown in  FIG. 16  by pushing the body  252  towards the spray gun  1  to re-position the plug  282  in the opening  285  and seal the ports in the end of the spout  256 . The reservoir  251  can then be detached from the spray gun  1  by pulling the finger grips  291  towards the body  252  to release the locking ribs  295  as described previously. The reservoir  251  can then be detached by continuing to pull the finger grips  251  to disengage the sleeve  283  from the adapter  296 . 
     As will be appreciated the action of pulling the finger grips  291  to first release the locking ribs  295  from the adapter  296  and then remove the sleeve  283  from the adapter  296  maintains the valve device  280  in the closed position. 
     When the reservoir  251  is detached from the spray gun  1 , it can be put to one side to store any unused paint for later use if required or thrown away. When storing unused paint in the reservoir  251  for re-use, the plug  282  can be wiped clean to prevent any paint drying and providing a source of contamination when it is desired to re-use the stored paint. This also prevents any paint drying and preventing the valve device  280  being opened when the reservoir  251  is re-attached to the spray gun  1 . The valve device  280  also prevents entry of any external contaminants to the paint while it is being stored in the reservoir  251 . 
     It will be understood that the valve device  280  may be employed with any of the other reservoirs  51 , 151  previously described according to the present invention. It will also be understood that any of the features of the various embodiments of the reservoir  51 , 151 , 251  according to the present invention may be employed with any of the other embodiments separately or in combination. 
     For example, the retainer hooks  295  for securing the reservoir  251  to the spray gun  1  with the adapter  296  may be used in place of the bayonet formations and adapter  18  to secure any of the other reservoirs  51 , 151 . The sealable plug  60  in the body  52  of the reservoir  51  shown in  FIG. 9  may be provided in the body  152 , 252  of the other reservoirs  151 , 251 . The skirt  71  or dependent projections shown in  FIG. 10  may be provided on the body  152 , 252  of any of the other reservoirs  151 , 251  to provide a rigid support for standing the reservoir  151 , 251  in an upright position. 
     In the above-described embodiments, the reservoir  51 , 151 , 251  contains a single liquid with the option of a sealable plug providing a one-way entry port in the wall of the rigid body for introducing another component. It will be understood, however that the reservoir could have internal compartments separated by a rupturable membrane whereby reactive components may be stored separately and mixed immediately prior to use. 
     As will now be appreciated, the present invention provides a reservoir of simple construction that is collapsible in a reliable, controlled manner to ensure that substantially all of the liquid in the reservoir can be dispensed. Moreover, the arrangement of a flexible diaphragm collapsible into a rigid body is such that stability of the reservoir on the spray gun is maintained when the reservoir is full, partially full and empty. As a result, the reservoir can be connected to the spray gun, partially used, disconnected, stored for later use and discarded when empty or no longer required. 
     The present invention further provides a reservoir that is especially suitable for supply to the end user pre-filled with the liquid to be dispensed. In this way, the end user only has to select and attach the appropriate reservoir and, after use, the reservoir can be removed and either stored for further use or thrown away. As a result, exposure of the user to health risks associated with handling the liquid is avoided and, after use, only the spray gun requires cleaning. 
     It will be understood, however, that the present invention is not limited to pre-filled reservoirs for supply to the end user. Thus, the benefits and advantages of the reservoir constructions described herein that provide for substantially complete dispense of the liquid may be applied to reservoirs that are supplied empty for the end user to fill and attach to the spray gun. 
     It will be appreciated that the exemplary embodiments described herein are intended to illustrate the diverse range and application of the invention and that features of the embodiments may be employed separately or in combination with any other features of the same or different embodiments. 
     It will be understood that the invention is not limited to the exemplary embodiments and that various modifications and improvements can be made within the spirit and scope of the invention as generally described herein.