WO2008003509A1

WO2008003509A1 - Freeze dryer

Info

Publication number: WO2008003509A1
Application number: PCT/EP2007/006005
Authority: WO
Inventors: Franciscus Antonius Damen; Jan Vugts; Johannes Van Veen; Josef Antonius Willem Maria Corver
Original assignee: The Boc Group Plc
Priority date: 2006-07-03
Filing date: 2007-07-02
Publication date: 2008-01-10
Also published as: GB0613082D0

Abstract

A freeze dryer (10) comprises a chamber (12) housing a plate (22) from which a plurality of shelves (20) is suspended. The shelves (20) are suspended from the plate (22) by links (28) carrying stops (38) upon which the shelves (20) rest to form a stack of vertically spaced shelves. Shelf support surfaces (200) are movable relative to the chamber (12) between adjacent shelves (20) in the stack. As the shelf stack is lowered within the chamber, the movement of the uppermost of these adjacent shelves is checked by the shelf support surfaces (200) so that, with further lowering of the shelf stack, the spacing between the adjacent shelves (20) increases. This can enable a pusher bar to fit between these two shelves to remove containers from, or load containers on to, the lowermost of these two shelves.

Description

FREEZE DRYER

The present invention relates to a freeze dryer.

Freeze dryer shelves are located within a chamber of a freeze dryer for receiving a plurality of containers or vials containing the product to be freeze dried. The chamber usually includes a number of shelves, each of which can be raised and lowered within the chamber. To load the shelves, the shelves are initially collapsed in the lower portion of the chamber, and the uppermost shelf is first moved into a loading position. A pack of containers is then loaded on to the shelf. After that shelf has been loaded, the loaded shelf is raised to enable the next shelf to be moved to the loading position. Following the loading of that shelf, all of the loaded shelves, and the next shelf to be loaded, are simultaneously raised until the next shelf to be loaded in located at the loading position. This moving sequence continues until the chamber loading has been completed. The freeze drying process is then performed within the chamber. Once the freeze drying process has been completed, the final shelf to be loaded is unloaded first. The other loaded shelves are then in turn lowered to the loading position, with the unloaded shelves being brought together in the lower portion of the chamber.

Freeze driers with automatic loading and unloading systems typically comprise a pushing mechanism located on one side of the chamber for pushing containers from a conveyor on to a shelf. A second pushing mechanism may be provided on the opposite side of the chamber for pushing containers from the shelf back on to the conveyor following the completion of the freeze drying process. Consequently, when a shelf is to be loaded or unloaded, the spacing between that shelf and the shelf located immediately above that shelf must be large enough to allow the pushing mechanism to pass freely between these shelves. This is normally achieved by arranging the loaded shelves, which are located at and above the loading position, in a vertical stack having a regular shelf pitch or spacing that is at least sufficient to enable the pushing mechanism to pass freely between those shelves, and which is maintained as the stack is vertically moved during the loading and unloading procedures.

The maintenance of this regular pitch between loaded shelves can add significantly to the overall height of the freeze dryer. Consequently, high capacity freeze dryers tend to be very tall, and this can lead to problems in accommodating such a freeze dryer in a user's facility, where there may be severe constraints on the possible locations, if any, of such a freeze dryer.

In a first aspect the present invention provides a freeze dryer comprising a chamber housing a stack of vertically spaced shelves, each shelf being vertically moveable separately from the other shelves in the stack, means for vertically moving the shelf stack within the chamber, and check means moveable relative to the chamber between adjacent shelves of the shelf stack for at least partially checking vertical movement of a shelf at a selected location within the chamber.

By enabling the shelves within the stack to be moveable separately from the other shelves within the stack, the location of check means between adjacent shelves can enable the distance between two shelves to be selectively increased. For example, as the shelf stack is lowered, a shelf may be checked at a particular height above a loading position at which containers are loaded on to, or unloaded from, a shelf. With further lowering of the shelf stack, the spacing between the shelf that has been checked at the selected position and the shelf located immediately beneath that checked shelf will increase. Consequently, when that lower shelf has reached the loading position, the distance between the lower shelf and the checked shelf can be sufficient to enable part of an unloading mechanism to pass between those shelves to unload the lower shelf. As a result, the loaded shelves in the shelf stack may be arranged so that the vertical spacing between these shelves is smaller than the spacing required to load containers on to the shelves. When a shelf is to be unloaded, the check means may be inserted between that shelf and the shelf immediately above that shelf so that, as the shelf stack is lowered, the spacing between those two shelves alone is increased due to the checked motion of the uppermost of these two shelves. This can enable either the overall height of the freeze dryer to be reduced in comparison to the prior art freeze dryer discussed above, or the capacity of a freeze dryer to be increased by enabling a greater number of shelves to be accommodated within the freeze dryer.

The check means preferably comprises shelf support surfaces for supporting a shelf at said selected location within the chamber to check movement thereof. These surfaces may be conveniently positioned between adjacent shelves of the shelf stack so that the uppermost of these shelves comes to rest upon these surfaces as the shelf stack is lowered.

When the shelf support surfaces are moved between the shelves of the shelf stack, the support surfaces may be horizontally aligned so that a shelf is checked in a substantially horizontal orientation within the chamber.

The shelf support surfaces are preferably independently moveable relative to the chamber. By moving, for example, a single support surface between shelves of the shelf stack, the movement of a shelf at the selected location may only be partially checked as the shelf stack is lowered, so that this shelf begins to tilt. This can be beneficial in draining fluid from the upper surface of the shelf. Freeze dryers are often provided with a clean in place (CIP) system in which nozzles spray water and detergents on to the shelves during the cleaning process. Tilting of a shelf following the cleaning process can enable residual cleaning fluid or water remaining on the upper surface of the shelf to be drained from the shelf, which can reduce the shelf drying time. Therefore, in a second aspect the present invention provides a freeze dryer comprising a - A -

chamber housing a stack of vertically spaced shelves, each shelf being vertically moveable separately from the other shelves in the stack, means for vertically moving the shelf stack within the chamber, and check means moveable between adjacent shelves of the stack for engaging one of the shelves as the shelf stack is vertically moved to cause the shelf to tilt.

A shelf may be tilted by moving only a reduced number of support surfaces between the shelves of the shelf stack, or by vertically staggering the support surfaces so that the shelf is tilted, for example by 2 - 3°, when it comes to rest upon the support surfaces.

Each shelf support surface is preferably located on a respective shelf support moveable relative to the chamber. Each shelf support is preferably rotatably moveable relative to the chamber so that the shelf support surfaces may be reliably and quickly moved between the shelves as required. In the preferred embodiment, the shelf supports are located on opposite sides of the chamber.

The check means may be configured to additionally at least partially check vertical movement of another shelf at a second selected location within the chamber. In a first example, the check means may be configured to additionally check vertical movement of the shelf located immediately above said shelf in the shelf stack. Depending on the pitch of the loaded shelves within the shelf stack, and the height of any containers loaded on to the shelves, as the lower shelf located beneath the checked shelf is lowered to the loading position the shelf located immediately above the checked shelf could come into contact with containers located on the checked shelf. This may be prevented by checking the movement of this upper shelf at a second location at which the shelf will be spaced from any containers loaded on the checked shelf.

In a second example, the check means is configured to additionally at least partially check vertical movement of the shelf located immediately below said shelf in the shelf stack. This second selected location may be the loading position for unloading containers from a shelf of the freeze dryer. By stopping the shelf at the loading position, there is no requirement to accurately stop the movement of the shelf stack so that a shelf is located at this loading position.

In either of the above examples, the check means may be configured to at least partially check vertical movement of shelves at the first and second selected locations at respective different times. In both of these examples, a shelf is first checked at the first location, and then as the shelf stack is lowered further another shelf becomes checked at the second location. The check means preferably comprises second shelf support surfaces for supporting a shelf at the second selected location, which may each be located on a respective one of the shelf supports. Consequently, the first and second shelf support surfaces may be simultaneously located between the shelves of the stack for checking the movement of shelves at the first and second locations.

The check means may be further configured to check the movement of shelves at other locations in the chamber. For example, the first and second examples mentioned above may be combined so that the movement of three adjacent shelves may be checked at different locations within the freeze dryer. The movement of these shelves may be checked at respective different times. For example, the shelf located immediately above the shelf to be unloaded may be checked first, followed by the shelf located immediately above that shelf (to prevent the shelf coming into contact with containers located on the first shelf to be checked), and finally the shelf to be unloaded may be checked at the loading position whilst the shelf stack is lowered.

The check means may therefore further comprise second shelf support surfaces for supporting a shelf at the second selected location, and third shelf support surfaces for supporting a shelf at the third selected location. Each shelf support may have located thereon a second shelf support surface and a third shelf support surface, so that the various support surfaces may be simultaneously moved between shelves of the shelf stack.

A screw system may be provided for moving the shelf stack within the freeze dryer, but in the preferred embodiment the shelves are suspended from a plate, for example a pressure plate, by links carrying stops upon which the shelves rest to form the shelf stack, and so the means for vertically moving the shelf stack may comprise an actuator for moving the plate vertically within the chamber. Therefore, in a third aspect, the present invention provides a freeze dryer comprising a chamber housing a plate from which a plurality of shelves are suspended by links carrying stops upon which the shelves rest to form a stack of vertically spaced shelves, an actuator for lowering the plate to lower the shelf stack within the chamber, and at least one shelf support surface moveable relative to the chamber between adjacent shelves for at least partially checking vertical movement of a shelf at a selected location within the chamber. As a shelf comes into contact with a support surface, the shelf rests upon that support surface, and becomes separated from one or more of its stops with further lowering of the shelf stack.

The links may be provided by chains or other flexible members, but preferably comprise rods slidably connected to the plate. A plurality of sets of rods may be provided, with each shelf being slidably connected to a respective different number of sets of rods. Each set of rods preferably carries a set of stops for supporting horizontally a respective shelf.

The shelves may be regularly spaced within the shelf stack before movement of any of the shelves is checked, and this spacing may be smaller than that required to load containers on to the shelves. Means may be provided for varying the regular spacing of the shelves within the stack. For example, for shelves that are suspended from a plate by links, additional stop members may be removably attached to at least some of the links to adjust the spacing between the shelves. Features described above in relation to the first aspect are equally applicable to the second and third aspects, and vice versa.

Preferred features of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a side view of an embodiment of a freeze dryer;

Figure 2 is a front view of the shelf stack of the freeze dryer of Figure 1 , illustrating links by which the shelves are suspended from an upper pressure plate;

Figure 3 is a simplified front view of the shelf stack, with shelf supports in a stowed position;

Figure 4 is a similar view to Figure 3, with shelf supports in a deployed position between adjacent shelves of the shelf stack;

Figure 5 is a similar view to Figure 3, with the shelf stack lowered to bring a first shelf into contact with first shelf support surfaces of the shelf supports;

Figure 6 is a top view of a shelf supported by shelf support surfaces;

Figure 7 is a similar view to Figure 3, with the shelf stack lowered further to bring a second shelf into contact with second shelf support surfaces of the shelf supports;

Figure 8 is a similar view to Figure 3, with the shelf stack lowered further to bring a third shelf into contact with third shelf support surfaces of the shelf supports; Figure 9 is a similar view to Figure 3, with one of the shelf supports in a deployed position;

Figure 10 is a simplified front view of the shelf stack, with alternative shelf supports in a deployed position;

Figure 11 is a similar view to Figure 10, with the shelf stack lowered to tilt a shelf checked by the lower support surfaces of the shelf supports;

Figure 12 is a side view of a freeze dryer with a tilted shelf;

Figure 13 is a close-up of part of Figure 2;

Figure 14 is a similar view to Figure 13, but with stop members attached to some of the links to adjust the spacing between shelves in the shelf stack; and

Figure 15 is an isometric view of the shelves of the freeze dryer, with stop members attached to all of the links to adjust the spacing between shelves in the shelf stack.

With reference first to Figure 1 , a freeze dryer 10 comprises a chamber 12 having a slot formed in the front wall 14 of the chamber 12 to enable containers or vials to be loaded into and unloaded from the chamber 12. The slot is selectively opened and closed by a slot door 16 moveable relative to the chamber 12 by a slot door moving mechanism. An opening 18 may be optionally provided on the rear wall 19 of the chamber 12, the opening 18 being located opposite to the slot formed in the front wall 14 of the chamber 12. The chamber 12 includes a number of substantially horizontal shelves 20 upon which containers are located within the chamber 12. As described in more detail below, each shelf can be raised and lowered within the chamber 12 to enable containers to be loaded on to the shelves 20. The shelves 20 additionally serve to transfer heat between a diathermic fluid such as alcohol, glycol, or silicone oil, and the products to be freeze-dried. The shelves 20 are connected by flexible hoses to an external refrigeration circuit (not shown) which cools diathermic fluid and conveys the diathermic fluid to the shelves 20. The diathermic fluid circulates within channels located within the shelves 20 in order to cause heat to be transferred from the products to the diathermic fluid and thereby cause freezing of moisture contained within the products. After freezing, the chamber 12 is evacuated to a pressure below 1 mbar, and the diathermic fluid is heated by an external heater (not shown) to cause the ice within the products to sublimate into water vapour.

A pressure plate 22 is located within the chamber 12 above the shelves 20. With reference to Figures 2 and 13, the pressure plate 22 is provided with brackets 26 at each corner thereof, and which each extend horizontally outward from the pressure plate 22. Each bracket 26 has a series of openings passing vertically therethrough for receiving links by which the shelves 20 are suspended from the pressure plate 22. In this embodiment, the links are provided by a plurality of sets of rods 28, each set comprising four rods of the same length. The sets of rods 28 have various different lengths. The rods 28 include first end stops 30 connected to the upper ends of the rods 28 and which, in this embodiment, normally rest upon the upper surfaces of the brackets 26 to limit, in a downwards direction, vertical movement of the rods 28 relative to the brackets 26.

Each shelf 20 comprises brackets 34 at each corner thereof, each bracket 34 extending horizontally outward from its respective shelf 20. Each bracket 34 has a series of openings passing vertically therethrough and each for slidably receiving a respective rod 28. Each set of rods 28 passes through openings located in the brackets 34 of the shelf 20 suspended by that set of rods 28, and through openings located in the brackets 34 of the shelves 20 located between that shelf 20 and the pressure plate 22. The rods 28 include second end stops 38 connected to the lower ends of the rods 28, and upon which a shelves 20 rest as they are moved vertically within the chamber 12.

Figures 1 and 2 illustrate the shelves 20 in a fully expanded arrangement, in which the first end stops 30 of the rods 28 rest upon the upper surfaces of the brackets 26, and each shelf 20 rests upon a set of second end stops 38. The shelves 20 form a stack of vertically spaced shelves, in which the shelves have a regular pitch or vertical spacing between adjacent shelves in the stack. In this embodiment, the length of the rods 28 determines the spacing between the shelves 20 in the expanded shelf stack.

Vertical movement of the shelf stack within the chamber 12 is controlled by an actuator 40 for moving the pressure plate 22 vertically within the chamber 12. The actuator 40 may be electrically, hydraulically or pneumatically driven. In this embodiment, the actuator 40 comprises a hydraulic cylinder 42 connected to an actuating arm 44 projecting into the chamber 12 and connected to the pressure plate 22. The actuating arm 44 is isolated from the sterile environment of the chamber 12 by bellows 46 surrounding the exposed portion of the actuating arm 44 extending from the hydraulic cylinder 42. The bellows 46 has one end attached to the pressure plate 22 and another end attached to the hydraulic cylinder 42 so that the bellows 46 can expand and contract as the arm is moved into and out from the chamber 12.

The lowering of the pressure plate 22 within the chamber 12 can adjust the arrangement of the shelves within the chamber 12 from the fully expanded position illustrated in Figure 2 to a collapsed position. As the pressure plate 22 is lowered, the second end stops 38 supporting the lowermost shelf in the shelf stack come to rest upon the floor of the chamber 12. Alternatively, a lower pressure plate may be positioned towards the bottom of the chamber 12 for supporting the lower surface of the lowermost shelf in the shelf stack.

With further lowering of the shelf stack, the lower surface of the shelf which is located immediately above the lowermost shelf comes to rest upon the upper surface of the lowermost shelf. This piling of the shelves, one upon the other, at the bottom of the chamber 12 may continue as the pressure plate 22 is lowered until all of the shelves have been piled up in the collapsed position.

In order to enable containers to be loaded on to one or more of the shelves 20, the pressure plate 22 is moved until the first shelf to be loaded has been raised from the pile and positioned at a loading position for receiving containers, for example, from a loading mechanism 50. The location of the loading position is indicated by the horizontal line 52 in Figure 1 , and is positioned at a height h. When a shelf is positioned at the loading position, the upper surface of that shelf is horizontally aligned with line 52. The slot door 16 is raised to open the slot, and containers are loaded on to the shelf. Once that shelf has been loaded, the pressure plate 22 is moved to position the shelf located immediately beneath the loaded shelf at the loading position. Containers are then loaded on to that shelf. This sequence is repeated until all of the containers have been loaded into the freeze dryer. The slot door 16 is then lowered to seal the slot, and the freeze drying process is performed within the chamber 12.

During the freeze drying process, stoppers are loosely located on the mouths of the containers to enable the water vapour to sublimate from the samples located within the containers. The shelves 20 may be used to press the stoppers into the containers upon completion of the freeze drying process. This has the advantage of sealing the containers within a controlled environment.

In this example, to close the containers the pressure plate 22 is lowered so that the second end stops 38 supporting the lowermost shelf in the shelf stack come to rest upon the floor of the chamber 12. With further lowering of the shelf stack, the lower surface of the shelf which is located immediately above the lowermost shelf comes to rest upon the upper surfaces of the stoppers located within the mouths of the containers located on the lowermost shelf. As the pressure plate 22 is further lowered, each of the other loaded shelves comes to rest, in turn, on the stoppers located within the mouths of the containers located on the shelf immediately beneath that shelf. Continued lowering of the pressure plate 22 causes the spacing between all of the loaded shelves to be simultaneously reduced, depressing the stoppers into the containers to form air-tight seals.

To unload the containers from the chamber 12, the pressure plate 22 is moved to locate the lowermost shelf at the loading position. The slot door 16 is raised to enable an unloading mechanism 54 to unload the shelf by pushing the containers from the shelf using a pusher rod 56 which enters the chamber 12 through the opening 18 and pushes the containers through the slot. Once the shelf has been unloaded, the pressure plate 22 is moved to locate another shelf at the loading position, and that shelf is then unloaded. This sequence is repeated until all of the shelves have been unloaded.

The positioning of a shelf at the loading position will now be described in more detail with reference to Figures 3 to 8. The links from which the shelves 20 are suspended from the pressure plate 22 have been omitted for clarity purposes only.

The chamber 12 houses n shelves, which are labelled from the bottom shelf 12O₁ to the top shelf 12O_n as 120i, 12O₂, 12O₃ ... 120_(n-2), 120_(n-i) and 12O_n. In this embodiment, the chamber houses 17 shelves upon which containers may be loaded. The uppermost shelf 122 is fixed to the pressure plate 22 so that, when stoppering is performed within the chamber 12, the temperature of the surface contact the stoppers of the containers located on shelf 120i₇ is the same as that of shelf 120i₇. The spacing between the upper surface of shelf 120i₇ and the lower surface of shelf 122 is ck. whereas the spacing between the upper surface of each of the other shelves 12O₁ to 12O₁₆ and the lower surface of the shelf located immediately above that shelf is d_1t where d₂ > di, and where only ck is sufficient to enable containers to be loaded on to, or unloaded from, a shelf. Line 52 illustrates the horizontal position of a shelf when located at the loading position, whilst line 58 locates the horizontal position of shelf 120₃ which is, by way of example, to be located at the loading position. The shelf stack is initially positioned such that the distance between lines 52 and 58 is d_x, where d_x < O₁.

The spacing di between the shelves in the expanded shelf stack illustrated in Figure 3 is sufficient to accommodate containers on the shelves, but is insufficient to enable the loading or unloading mechanisms to be inserted between the shelves. For this purpose, the spacing between the shelf to be loaded, or unloaded, and the shelf located immediately above that shelf needs to be increased, in this example to d₂.

To increase the spacing between at least these shelves in the shelf stack, the freeze dryer comprises a pair of shelf supports 200 located on opposite sides of the chamber 12. In this example, each shelf support 200 carries three sets of spaced shelf support surfaces 202, 204, 206. An actuator 208 is connected to each shelf support 200 for actuating movement of the shelf support 200 from the stowed position illustrated in Figure 3 to a deployed position illustrated in Figure 4, in which the shelf support surfaces are located between adjacent shelves of the shelf stack. The distance d_x is chosen so that the shelf supports 200 are able to freely move between the stowed and deployed positions without coming into contact with any of the shelves.

The actuators 208 may be electrically, hydraulically or pneumatically driven. In this embodiment, each actuator 208 comprises a hydraulic cylinder 210 connected to an actuating arm 212 projecting into the chamber 12 and pivotally connected to the shelf support 200. The hydraulic cylinder 210 is isolated from the sterile environment of the chamber 12 by bellows 214 surrounding part of the actuating arm 212. The end of the actuating arm 212 that is located within the chamber 12 is connected to pivot 216 of the actuator 208 such that linear movement of the actuating arm 212 relative to the chamber 12 results in rotation of the shelf support 200 relative to the chamber 12.

In order to increase to d₂ the spacing between the lower surface of shelf 12O₄ and the upper surface of shelf 120₃ when located at the loading position, the pressure plate 22 is first moved to the position illustrated in Figure 3. The shelf supports 200 are then rotated to the deployed position shown in Figure 4, so that shelf supports 202 are co-planar and are located between shelves 12O₄ and 12O₅, shelf supports 204 are co-planar and are located between shelves 12O₃ and 12O₄, and shelf supports 206 are co-plahar and are located between shelves 12O₂ and I2O₃.

The pressure plate 22 is then lowered to position shelf 12O₃ at the loading position. As the shelf stack is lowered, shelf 12O₄ first comes into contact with shelf support surfaces 204, as illustrated in Figure 5. The movement of shelf 12O₄ is thus checked so that, with further lowering of the pressure plate 22, the spacing between shelf 12O₃ and shelf 12O₄ increases.

Figure 6 is a top view of shelf 12O₄ supported by shelf support surfaces 204. In this embodiment, each shelf support 200 carries two spaced shelf support surfaces 204, each for supporting a shelf towards a respective corner thereof.

Two shelf support surfaces 202, and two shelf support surfaces 206 may be similarly positioned, at different heights, on each shelf support 200.

Alternatively, for any of the shelf support surfaces 202, 204, 206, the two shelf support surfaces may be replaced by any other number of shelf support surfaces. For example, a single shelf support surface may extend substantially along the length of the shelf support 200.

As the shelf stack is lowered further, shelf 12Os comes into contact with shelf support surfaces 206, as illustrated in Figure 7 so that the distance between the upper surface of shelf 12O₄ and the lower surface of shelf 12Os becomes fixed at a value of G^, where d₃ < du In the event that the shelves are loaded, selection of the value of cfo to be greater than the height of any containers located on shelf 12O₄ can prevent shelf 12O₅ from coming into contact with these containers. In this position, the spacing between the upper surface of shelf 12O₃ and the lower surface of shelf 12O₄ has a value of d₄, where d₂ > d₄ > di. With further lowering of the pressure plate 22, shelf I2O₃ comes into contact with shelf support surfaces 202 so that the upper surface of shelf 12O₃ is level with horizontal line 160, as illustrated in Figure 8, and so that the distance between the upper surface of shelf 12O₃ and the lower surface of shelf 12O₄ has a value of d∑. This can enable containers to be loaded on to, or unloaded from, shelf 12O₃.

As also illustrated in Figure 8, the spacing between the upper surface of shelf 12O₅ and the lower surface of shelf 12O₆ is now d₅, where d₅ < d-_\. In the event that d₅ is smaller than the height of the containers, then further shelf support surfaces may be located on the shelf supports 200 for checking movement of this shelf in order to prevent it from coming into contact with containers located on shelf 12O₅ as shelf 12O₃ is lowered to the loading position. The spacing d₂ between the upper surface of shelf 120i₇ and the lower surface of shelf 122 enables shelf 120i₇ to be loaded or unloaded without requiring use of the shelf support surfaces, as the proximity of the pressure plate 22 to that shelf prevents the shelf supports 200 from being maintained at their deployed positions during loading or unloading of that shelf.

By use of the shelf supports 200 to selectively increase the spacing between adjacent shelves, the normal spacing between the facing surfaces of adjacent loaded shelves can be reduced by around 15 - 25 % in comparison to a freeze dryer in which the spacing between these surfaces is fixed at a value that enables the shelves to be loaded.

The provision of shelf support surfaces 202, 206 is optional. For example, if the height of containers to be loaded on to the shelves is such that the shelf 12O₅ would not come into contact with the containers located on shelf 12O₄ when shelf 12O₃ has been positioned at the loading position, the shelf support surfaces 206 may be omitted. The provision of shelf support surfaces 202 is optional, but can enable a shelf to be accurately located at the loading position without having to accurately stop the movement of the pressure plate 22 to locate that shelf at the loading position; the movement of the pressure plate 22 can be stopped at any time after the shelf has become located on the shelf support surfaces 202 but before any of the other shelves come into contact with any containers.

The freeze dryer 10 is provided with a clean in place (CIP) system for cleaning the shelves following the completion of a freeze drying process. For example, the freeze dryer 10 may comprise a series of nozzles for spraying water and detergents on to the shelves during the cleaning process.

After this process, a considerable amount of cleaning fluid and/or condensation may remain on the upper surfaces of the shelves. In order to drain fluid from the shelves, as illustrated in Figure 9, the shelves may be tilted in turn through movement of a single shelf support 200 into a deployed position whilst the other shelf support remains in the stowed position.

Consequently, as the pressure plate 22 is lowered within the chamber 12, one of the shelves comes into contact with support surfaces located on the deployed shelf support. In the example illustrated in Figure 9, shelf 120i comes into contact with shelf support surfaces 204 carried by the deployed shelf support 200. With further lowering of the shelf stack, shelf 120i will rotate (in an anti- clockwise direction as viewed in Figure 9) about a horizontal axis co-linear with the line of contact between the lower surface of shelf 120i and the shelf support surfaces 204. The extent to which the selected shelf may tilt within the chamber 12 will be limited by the amount of play between the shelf and the rods 28 passing through the apertures 36 in the brackets 34 of that shelf. For example, the maximum inclination of the shelf to the horizontal may be 2-3°. Movement of the shelf stack may be stopped before this maximum is reached in order to incline the shelf by a pre-selected amount.

Once a shelf has been held in an inclined position for a period of time, the shelf stack may be raised in order to lift the shelf from the shelf support surfaces 204. The deployed shelf support 200 is rotated to the stowed position to enable the shelf stack to be freely raised and lowered within the chamber 12. The shelf stack may then be moved to position another shelf in position for tilting.

As an alternative to using a single shelf support 200 to partially check movement of a shelf, an additional support surface may be located on each shelf support 200 so that movement of a shelf is partially checked when that shelf comes into contact with these additional support surfaces. With reference to Figures 10 to 12, each shelf support 200 may have an additional shelf support surface 302 for supporting a shelf towards a corner thereof. In this embodiment, each additional shelf support surface 302 is located beneath a respective shelf support surface 206. Figure 10 illustrates the shelf stack positioned so that shelf 120i is partially supported by the additional shelf support surfaces 302. As the shelf stack is lowered to the position illustrated in Figures 11 and 12, the shelf 120i rotates (in an anti- clockwise direction as viewed in Figure 12) about a horizontal axis co-linear with the line of contact between the lower surface of shelf 12O₁ and the additional shelf support surfaces 302. Again, the extent to which the selected shelf may tilt within the chamber 12 will be limited by the amount of play between the shelf and the rods 28 passing through the apertures 36 in the brackets 34 of that shelf.

Returning to Figure 13, in the embodiment described above in a fully expanded arrangement of the shelves the first end stops 30 of the rods 28 rest upon the upper surfaces of the brackets 26, and each shelf 20 rests upon a set of second end stops 38 so that the shelves have a regular spacing of di. As illustrated in Figure 13, at least some of the sets of rods 28 may be provided with at least one portion 320 of reduced cross-section. This can enable temporary stop members 322 to be removably attached to the rods 28 at the locations of the portions 320 of reduced cross-section. As illustrated in Figure 14, the removable stop members 322 are attached to the rods 28 when the portions 320 of reduced cross-section have been raised above the brackets 26 of the pressure plate 22. When the rods 28 are released from this raised position, the removable stop members 322 come to rest upon the upper surface of the brackets 26 of the pressure plate 22. This can have the effect of varying the spacing between the shelves in the shelf stack.

With reference to Figured 4, by attaching removable stop members 322 to alternate sets of rods 28, every other shelf may be moved so that it is brought up against the shelf located immediately above that shelf. This has the effect of effectively doubling the space between adjacent shelves, enabling the freeze dryer to accommodate taller containers. With reference to Figure 15, by attaching removable stop members 322 to the sets of rods so that the ' positions of the end stops 30 are staggered, the spacing between adjacent shelves may be reduced.

Figure 15 also illustrates a set of nozzles 350 which may be positioned to spray detergent on to a shelf during a CIP process. The nozzles 350 may be conveniently mounted on shafts 352 which may support guide rails 354 for guiding movement of the containers during the loading and unloading procedures. The shafts 352 may be rotatable relative to the chamber 12 to position the guide rails 354 between adjacent shelves. The actuators 356 for actuating the movement of the shafts 352 may be similar to the actuators 208 for actuating movement of the support arms 200.

Claims

1. A freeze dryer comprising a chamber housing a stack of vertically spaced shelves, each shelf being vertically moveable separately from the other shelves in the stack, means for vertically moving the shelf stack within the chamber, and check means moveable relative to the chamber between adjacent shelves of the shelf stack for at least partially checking vertical movement of a shelf at a selected location within the chamber.

2. A freeze dryer according to Claim 1 , wherein the check means comprises shelf support surfaces for supporting a shelf at said selected location within the chamber to check movement thereof.

3. A freeze dryer according to Claim 2, wherein the shelf support surfaces are independently moveable relative to the chamber.

4. A freeze dryer according to Claim 2 or Claim 3, comprising shelf supports moveable relative to the chamber and each having at least one shelf support surface located thereon.

5. A freeze dryer according to Claim 4, wherein each shelf support is rotatably moveable relative to the chamber.

6. A freeze dryer according to Claim 4 or Claim 5, wherein the shelf supports are located on opposite sides of the chamber.

7. A freeze dryer according to any preceding claim, wherein the check means is configured to at least partially check vertical movement of a shelf at a second selected location within the chamber.

8. A freeze dryer according to Claim 7, wherein the check means is configured to at least partially check vertical movement of shelves at the first and second selected locations at respective different times.

9. A freeze dryer according to Claim 8, wherein the check means is configured to check vertical movement of the shelf located immediately above said shelf in the shelf stack.

10. A freeze dryer according to Claim 8, wherein the check means is configured to at least partially check vertical movement of the shelf located immediately below said shelf in the shelf stack.

11. A freeze dryer according to Claim 10, wherein the second selected location is an loading position for unloading containers from a shelf of the freeze dryer.

12. A freeze dryer according to any of Claims 7 to 11 , wherein the check means comprises second shelf support surfaces for supporting a shelf at the second selected location.

13. A freeze dryer according to Claim 12 when dependent upon any of Claims 4 to 6, wherein each shelf support has at least one second shelf support surface located thereon.

14. A freeze dryer according to Claim 10, wherein the check means is further configured to check, at a third selected location within the chamber, vertical movement of the shelf located immediately above said shelf in the shelf stack.

15. A freeze dryer according to Claim 14, wherein the check means is configured to check vertical movement of shelves at the first, second and third selected locations at respective different times.

16. A freeze dryer according to Claim 14 or Claim 15, wherein the check means comprises second shelf support surfaces for supporting a shelf at the second selected location, and third shelf support surfaces for supporting a shelf at the third selected location

17. A freeze dryer according to Claim 16 when dependent upon any of Claims 4 to 6, wherein each shelf support has located thereon at least one second shelf support surface and at least one third shelf support surface.

18. A freeze dryer according to any preceding claim, wherein the shelves are suspended from a plate by links carrying stops upon which the shelves rest to form said stack.

19. A freeze dryer according to Claim 18, wherein the plate is a pressure plate.

20. A freeze dryer according to Claim 18 or Claim 19, wherein the means for vertically moving the shelf stack comprises an actuator for moving the plate vertically within the chamber.

21 . A freeze dryer according to any of Claims 18 to 20, wherein the links comprise rods connected to the plate.

22. A freeze dryer according to Claim 21 , wherein the rods comprise a plurality of sets of rods, each shelf being slidably connected to a respective different number of sets of rods.

23. A freeze dryer according to Claim 22, wherein each set of rods carries a set of stops for supporting horizontally a respective shelf.

24. A freeze dryer according to Claim 23, comprising a plurality of stop members removably attachable to the rods to adjust the spacing between shelves in the shelf stack.

25. A freeze dryer comprising a chamber housing a plate from which a plurality of shelves are suspended by links carrying stops upon which the shelves rest to form a stack of vertically spaced shelves, an actuator for lowering the plate to lower the shelf stack within the chamber, and at least one shelf support surface moveable between adjacent shelves of the shelf stack for at least partially checking vertical movement of a shelf at a selected location within the chamber.

26. A freeze dryer comprising a chamber housing a stack of vertically spaced shelves, each shelf being vertically moveable separately from the other shelves in the stack, means for vertically moving the shelf stack within the chamber, and check means moveable between adjacent shelves of the stack for engaging one of the shelves as the shelf stack is vertically moved to cause the shelf to tilt.