Background to the Invention Heat treating systems, commonly referred to as autoclaves, are used, for example, in the medical and dental environments for heat treating medical and dental instruments so that they are in a sterilised condition to comply with cleanliness regulations applicable to those environments.

While the invention has been developed particularly for use in the medical or dental environment, it will be appreciated that the same system, without any substantial modification, could be used in other applications, for example, as a pressure cooker for cooking foodstuffs or any other suitable heat treating application.

The applicant is aware of various autoclaves for use in medical or dental environments. However, these autoclaves have significant shortcomings, particularly in the time taken to complete a heat treating cycle. In heat treating medical or dental instruments, they are normally placed in a foraminous bag prior to insertion into the autoclave. The applicant has found that, after heat treatment, in almost all cases, the bag remains wet. Regulations normally require that, where a bag of sterilised instruments is to be stored, it must be dry before the door of the sterilising equipment is opened. The reason for this is that, if the bag is stored in a wet or damp condition, bacteria can migrate through the pores of the bag rendering the instruments unsafe for use. Sometimes paper bags are used and, if such bags are wet, the weight of the instruments in the bag can cause the bag to rupture resulting in the instruments falling out and becoming contaminated.

Normally flash sterilising, i. e. where the instruments can still be wet after sterilisation, is used where the instruments are intended for immediate use after sterilisation. The instruments may or may not be bagged.

Summary of the Invention According to a first aspect of the invention, there is provided a heat treating system which comprises

at least one double-skinned vessel with a gap defined between skins of the vessel, the vessel defining a chamber in which articles to be heat treated are receivable; a heat transfer fluid contained in the gap of the vessel ; a heater mounted to the vessel for heating the heat transfer fluid and maintaining the heat transfer fluid at a desired temperature ; and a vapour generating device in communication with the chamber of the at least one vessel for generating vapour to be fed into the chamber of the vessel to effect heat treatment of the articles in the chamber, in use.

According to a second aspect of the invention, there is provided a heat treating system which comprises at least one vessel that defines'a chamber in which articles to be heat treated are receivable; and a vapour generating device in communication with the chamber of the at least one vessel for generating vapour to be fed into the chamber of the vessel to effect heat treatment, in use, of the articles in the chamber, the vapour generating device being arranged adjacent the vessel to aid in temperature regulation of the chamber of the vessel.

Preferably, the system includes at least two vessels arranged alongside each other in spaced relationship, each vessel having a vapour generating device associated with it. The vapour generating devices may be arranged between the vessels. With this arrangement when one vessel is being used, the other can be filled and used without having to wait for the first vessel to complete its cycle. This improves the flexibility of the system.

The vessels may be mounted on a chassis to lie substantially horizontally, in use, in transversely spaced relationship with the vapour generating devices being mounted between the vessels in spaced relationship relative to each other. In a preferred configuration of the system, the vapour generating devices may be vertically stacked with respect to each other.

Each vessel may be in the form of a cylinder. Preferably, each vessel is in the form of a right circular cylinder having a first closed end and a second open end. The open end of each cylinder may be closed by means of a closure member or door.

The door may be mounted on a fluid operable system to be displaceable longitudinally with respect to its associated vessel.

Each vapour generating device may be in the form of a heat sink. Each heat sink may comprise a container in which a heating element and a quantity of heat absorbent bodies are contained.

The bodies may be arranged adjacent to and/or surrounding the heating element The bodies may be metal objects in the form of balls, rods, cones, or any other fabricated shape, such as a cast shape. When liquid comes into contact with the heated bodies, it flashes off into vapour to be fed into the chamber of its associated vessel.

In another embodiment of the invention, the bodies may be immersed in a heat retaining fluid and in a conduit for carrying liquid to be vaporised in the heat sink may extend through the heat sink. This embodiment of the invention is intended for larger systems. The conduit may follow a tortuous path through the heat sink. In this embodiment, the bodies may be scrap metal disks. It will be appreciated that, with the provision of the heat retaining fluid, which may be an oil, there is less need for spaces between the bodies. Thus the bodies can be packed closer together. In addition a greater weight per given heat sink can be achieved improving the efficiency of the heat sink. Further, the need for separate probes for controlling heating element and the heat sink temperature is obviated. Only one sensor is needed to control the temperature of the oil. The use of scrap metal for the bodies also lowers the cost of the heat sink.

Liquid fed to each vapour generating device may be water. The water may contain additives such as a sterilising fluid.

The heat transfer fluid may be in the form of an oil which fills the gap between the skins of the vessel. The gap may be in communication with an oil reservoir so that, when the oil expands as it is heated, overflow oil can be fed into the reservoir and, conversely, when the oil cools, oil can be withdrawn from the reservoir into the gap to maintain the gap substantially full of oil The oil reservoir may also be used for gathering overflow oil from the heat sink when the oil is used in the heat sinks as the heat retaining fluid.

An outer skin of the at least one vessel may be insulated to reduce the loss of heat to the atmosphere.

The heater may be arranged in a pod secured to an outer skin of the at least one vessel. As indicated above, the vessels may be arranged substantially horizontally and the pod may be arranged below a horizontal plane bisecting the at least one vessel to encourage convection heating and convective current flow of the heat transfer fluid.

The applicant believes that this will result in a more even heat distribution about the circumference of the vessel. The pod containing the heating means may be arranged at more than about 45'bellow the horizontal plane bisecting the vessel. Preferably, the pod is arranged between about 55-65'below the horizontal plane bisecting its associated vessel to facilitate the convection heating. Optimally, the pod is arranged at about 60° below the horizontal plane.

The applicant has also found that the heat sinks encourage a measure of convection flow of the oil in the gaps of the vessels and assist in causing an even distribution of heat about the circumference of the vessels.

The system may include an evacuating device for evacuating the chamber of the at least one vessel. The evacuating device may be in the form of a pump. Each vessel may have a pump associated with it.

Still further, the system may include a supply arrangement for supplying liquid to the vapour generating device. In one embodiment of the invention, the supply arrangement may be a liquid pump for pumping liquid into each heat sink to be converted into vapour to be injected into the chamber of its associated vessel. In another embodiment of the invention, the supply arrangement may comprise a liquid supply arrangement.

Accordingly, a third aspect of the invention provides a liquid supply arrangement which includes: a reservoir for containing a quantity of liquid; a container; a liquid supply line interconnecting the reservoir and the container to place an interior of the container in communication with an outlet of the reservoir; an interlock mechanism arranged in the liquid supply line, the interlock mechanism allowing liquid flow from the reservoir to the interior of the container when the interlock mechanism is in a first state and inhibiting liquid flow from the reservoir to the interior of the container when the interlock mechanism is in a second state; a pressurising controller in communication with the interior of the container for pressurising liquid in the container when the interlock mechanism is in its second state and which ceases pressurising liquid in the container when the interlock mechanism is in its first state; and a control mechanism for controlling the state of the interlock mechanism and the pressurising means, the control mechanism being responsive to a condition of a component of a system to be supplied with liquid from the container.

The component of the system may be a door lock of a door of a heat treating system, the door lock and the door being fluid operable and the door closing off a chamber of a vessel in which items to be heat treated are received, the interlock mechanism also being responsive to a state of the door of the system.

As indicated above, the liquid supply system may be used in conjunction with the heat treating system of the first and the second aspects of the invention in place of a liquid supply pump. The door of each vessel may be displaceable longitudinally with

respect to its associated vessel by means of one or more pneumatic rams. The door locking mechanism may also be fluid operable. Thus, the heat treating system may include a fluid reservoir in the form of an air reservoir for operating the door and the door locking mechanism, or door lock, for locking the door in its closed condition, in use.

The interlock mechanism may be a fluid operated valve which is open when the door lock of the door is unlocked and is closed when the door lock is locked.

The pressurising controller may be controlled by a lock control mechanism for the door lock so that, when the door lock is unlocked, no pressurising of liquid in the container occurs. Conversely, when the door lock is locked, the fluid operated valve is closed and the lock control mechanism permits the pressurising controller, which receives fluid from a source of fluid under pressure, to pressurise liquid in the container causing liquid to be expelled through the outlet of the container into at least one of heat sinks of the heat treating system.

The advantage of the liquid supply system over a conventional pump is that it is cheaper and lighter. Also, by varying the air pressure supplied to the water supply, variations in operating parameters can be achieved. Still further, because the pressure within the chamber during a cycle approaches the pressure of the water supply a point is reached where no further steam can be produced. The interlock mechanism inhibits the production of steam without the dor being locked which enhances the safety of the system as a whole.

A flow control unit may be arranged intermediate an outlet of the container and the system. The flow control unit may include a check valve and a solenoid valve.

When the door lock is unlocked, the solenoid valve may be closed and, conversely, when the door lock is locked, the solenoid valve may be open.

According to a fourth aspect of the invention, there is provided a door locking assembly for a door of a heat treating system, as described above, the door locking assembly including: a closure member for closing off an opening of the chamber of the at least one vessel of the heat treating system, the closure member defining at least one receiving formation; a locating formation associated with the at least one receiving formation of the closure member, the locating formation being in the form of an outwardly extending projection arranged at an end of the vessel defining the opening of the chamber ; and

a seat-defining portion associated with the at least one receiving formation of the closure member, the seat-defining portion defining a seat in which a part of the associated locating formation is received when the door is in its locked position, in use.

The closure member may include a carrier which is longitudinally displaceable relative to the vessel and a closure plate which is rotatably carried on the carrier. The closure plate may have an outwardly extending projection which is operated by a fluid operated control mechanism of the heat treating system for rotating the closure plate through a predetermined arc between an unlocked configuration and a locked configuration.

The closure plate may define a plurality of circumferentially spaced receiving formations. Each receiving formation may be in the form of an arcuate slot having an enlarged part proximate a first end of the slot with the seat-defining portion being arranged proximate an opposed end of the slot.

Each receiving formation may have a locating formation associated with it.

Each locating formation may be a stud having an enlarged head portion. The head portion may be dimensioned to be received through the enlarged part of its associated slot of the closure plate when the door is in its unlocked position and to seat in the seat of the seat-defining portion when the door is in its locked position.

Each seat may be in the form of a recess formed at the opposed end of its associated slot, the recess being dimensioned to accommodate the head portion of its associated stud snugly therein.

Those skilled in the art will appreciate that, during a heat treating cycle, the chamber of the vessel is pressurised. With the provision of the recesses, the likelihood of the door inadvertently rotating to an unlocked configuration and being forced open by the pressure within the chamber is reduced.

According to a fifth aspect of the invention, there is provided a method of drying items in a heat treating system, the method including: reducing pressure in a chamber of a vessel of the heat treating system; introducing cold fluid into the chamber to cause condensation of vapour in the chamber; introducing hot fluid into the chamber to expel condensed fluid through an exhaust port of the vessel; and cycling through the above steps a predetermined number of times.

The item may be a receptacle, such as a bag or basket, containing articles to be heat treated.

By"cold"means that the fluid has a temperature of less than about 20 to 40°C, preferably less than about 25°C and by"hot"means that the fluid has a temperature exceeding about 100 to 135°C, preferably above about 100°C.

The method may include monitoring the pressure in the chamber of the vessel and, if the pressure remains within a predetermined range of the pressure in the chamber for a predetermined period of time, reducing the number of steps in the drying cycle.

Brief Description of the Drawings Embodiments of the invention are now described by way of example with reference to the accompanying drawings in which: Figure 1 shows a three dimensional view of a heat treating system in accordance with an embodiment of a first and a second aspect of the invention; Figure 2 shows a schematic end view of part of the system of Figure 1 ; Figures 3a-3c show a sequence of steps in the use of a liquid supply arrangement, in accordance with an embodiment of a third aspect of the invention; Figure 4 shows a three dimensional, exploded view of a door locking assembly, in accordance with an embodiment of a fourth aspect of the invention; Figure 5 shows a fluid supply circuit for the heat treating system; Figure 6 shows a schematic, sectional, side view of a first version of a heat sink of the system; and Figure 7 shows a schematic, sectional, side view of a second version of a heat sink of the system.

Detailed Description of the Drawings Referring initially to Figure 1 of the drawings, a heat treating system, or autoclave, in accordance with an embodiment of first and second aspects of the invention, is illustrated and is designated generally by the reference numeral 10. The system 10 includes a chassis or frame 12 supporting a pair of vessels 14 in transversely spaced relationship. Each vessel 14 is closed off at a first end 14.1 and defines an opening 16 at an opposed end 14.2.

Each opening 16 is closed off by a closure member or door 18. It is to be noted, in Figure 1 of the drawings, that only one of the doors 18 is shown for the sake of clarity.

Each vessel 14 has a vapour generating device, or heat sink 20, associated with it.

The vessels 14 are substantially horizontally arranged on the chassis 12 and are transversely spaced with respect to each other.

As illustrated in Figures 1 and 2 of the drawings, the heat sinks 20 are arranged in vertically stacked, spaced relationship between the vessels 14.

Each heat sink 20 supplies vapour via a feed pipe 22 to a chamber 24 of its associated vessel 14.

Each vessel 14 and each heat sink 20 is surrounded by insulation but this insulation has been omitted from the Figure 1 of the drawings for the sake of explanation purposes.

Each vessel 14 is a double-skinned vessel having an outer skin 26 (Figure 2) and an inner skin 28. A gap 30 is defined between the outer skin 26 and the inner skin 28.

A heat transfer fluid in the form of an oil 32 substantially fills the gap 30 of each vessel 14. Each gap 30 is in communication with an oil reservoir 34 mounted on the chassis 12.

The outer skin 26 is spaced from the inner skin 28 by a distance of approximately 5mm. It will be appreciated that the same gap is provided at the closed end 14.1 of each vessel 14.

A longitudinally extending pod 36 is arranged along the outer skin 26 of each vessel 14 in communication with the gap 30. A heater 38 is contained in each pod 36 for heating the oil 32.

As illustrated more clearly in Figure 2 of the drawings, if one imagines a horizontal plane bisecting each vessel 14, each pod 36 lies below the horizontal plane.

Preferably, each pod 36 lies at about 5 o'clock or 7 o'clock (in the view of the vessels 14 illustrated in Figure 2). This encourages convection heating and flow of the oil 32 in the gaps 30 as illustrated by arrows 40.

In addition, the provision of the heat sinks 20 between the vessels 14. also enhances the convection current flow as illustrated by the arrows 40 to such an extent that the vessel wall operating temperatures are much more even and can operate at up to 25°C lower but providing the same result. This results in considerable cost savings as less power needs used in the heater 38. This has proved to be an unexpected, surprising result in that it was not anticipated that, by placing the heat sinks 20 between the vessels 14, such an improvement in operating performance would be achieved.

The system 10 includes an air pump 42 which supplies air to a reservoir 44. Air is supplied from the reservoir 44 to each vessel 14 to effect hot or cold air purging of the vessels 14, as will be described in greater detail below. Air from the reservoir 44 is also used to operate various pneumatic parts of the system 10.

Each door 18 of the vessel 14 is pneumatically operated to be displaceable longitudinally with respect to its associated vessel 14 via a pneumatic ram 46.

Each door 18 has a carriage 48 associated with it. Articles to be sterilised in the system 10 are placed in a receptacle, such as a bag or a basket, which, in turn, is placed on the carriage 48 to be positioned in the chamber 24 of the relevant vessel 10.

Referring now to Figures 3a-3c of the drawings, a liquid supply arrangement, in accordance with an embodiment of a third aspect of the invention for use with the system 10, is illustrated and is designated generally by the reference numeral 50.

The liquid supply arrangement 50 includes a water reservoir 52 having an outlet 54 which communicates via a feed line 56 with a water container 58. An interlock mechanism in the form of an air operated valve 60 is arranged in the feed line 56. The valve 60 allows water flow from the reservoir 52 to the container 58 when the valve 60 is in a first, open state and inhibits water flow from the reservoir 52 to the container 58 when the valve 60 is in a second, closed state.

The liquid supply arrangement 50 includes a pressurising means in the form of a normally open spool valve 62 which communicates with the air reservoir 44 of the system 10 via the air pump 42 and an air line 64.

The air operated valve 60 is controlled by a pneumatic lock control mechanism 66 which also controls operation of the valve 62 and a lock of the door 18. Also, the air pressure supply to the system is fitted with a pressure regulator (not shown) which facilitates adjustment of the volume of water supplied per steam generating pulse.

An outlet from the container 58 communicates with an inlet of its associated heat sink 20 via a check valve 68 and a solenoid valve 70.

In use, when it is desired to inject water into the heat sink 20, the solenoid valve 70 is closed and the air operated valve 60 is open. The lock control mechanism 66 is in an off state. The valve 62 is closed. Because the air operated valve 60 is open, water can drain from the reservoir 52 into the container 58, for example, under gravity.

However, as the solenoid valve 70 is closed, water cannot be fed from the container 58 into the heat sink 20.

To charge water into the heat sink 20, the lock control mechanism 66 is first switched to an on state. This will be done when the door 18 is locked in its closed position relative to its associated vessel 14. This closes the valve 60 inhibiting further supply of water from the reservoir 52 to the container 58. The interior of the container 58 is pressurised by opening the valve 62 so that air from the reservoir 44 is fed into the interior of the container 58 to pressurise the interior of the container 58. The solenoid valve 70 is opened and water can flow from the container 58 into the heat sink 20. The

solenoid valve 70 is then closed. From there, steam, as indicated generally at 72 in Figure 3b of the drawings, is fed via the supply line 22 into the chamber 24 of the relevant vessel 14. As and when further steam 72 is required to be generated for that heat treating cycle, the valve 70 is opened to allow the injection of further water from the container 58 to the heat sink 20. It is to be noted that, in a heat treating cycle, steam 72 is pulsed periodically into the chamber 24 of the vessel 14 until the required operating parameters have been reached (typically a pressure of about 207 kPa and a temperature of about 134'C). The operating parameters are maintained at the required values by management of vessel wall temperature for the duration of the sterilisation process.

Further charging of the container 58 with water can only be carried out after completion of a heat treating cycle when the door 18 has been unlocked. When that occurs, the lock control mechanism 66 reverts to its off position where the air operated valve 60 is again open as is the valve 62 so that the interior of the container 58 is no longer pressurised. When the lock control mechanism 66 reverts to its off position, excess air in the container 58 bleeds off to atmosphere via the valve 62. It is to be noted that the valve 62, when in its open position, allows air supply to a pneumatic cylinder (not shown) which rotates a closure plate 86 (Fig. 4) of the door 18 to an open or unlocked position. When the valve 62 closes, the closure plate 86 is rotated to its locked position.

In Figure 4 of the drawings, a door locking assembly, in accordance with an embodiment of a fourth aspect of the invention, for use in the system 10, is designated generally by reference numeral 80.

The door 18 includes a carrier plate 82 which is mounted on the pneumatic ram 46 and a door runner 84 (Figure 1). A closure plate 86 is rotatably carried on a first side of the carrier plate 82. The closure plate 86 has a radially outwardly extending finger 84 projecting beyond a periphery of the carrier plate 82, as illustrated in Figure 1 of the drawings. This finger 88 is engaged by an operating mechanism (not shown) for rotating the closure plate 86 through a predetermined arc relative to the carrier plate 82 and the vessel 14 for effecting locking and unlocking of the door 18 relative to the vessel 14. A sealing and insulating member 90 is carried on an opposed side of the carrier plate 82.

The closure plate 86 defines a plurality of circumferentially spaced receiving formations in the form of arcuate slots 92.

An equivalent number of locating formations in the form of studs 94 are carried on the end 14.2 of the vessel 14.

Each slot 92 has an enlargement 96 at one end which is dimensioned to receive an enlarged head 98 of one of the studs 94 when the carrier plate 82 abuts the end 14.2 of the vessel 14 and the closure plate 86 of the door 18 is in an unlocked configuration.

A seat defining formation, or recess, 100 is arranged at an opposed end of each slot 92 so that, when the closure plate 86 of the door 18 has been rotated to a locked position and the chamber 24 of the vessel 14 has been pressurised, in use, the head 98 of each stud 94 is received in one of the recesses.

It will be appreciated that, in operation, the chamber 24 of the vessel 14 is pressurised. When this occurs, the door 18 is urged slightly outwardly, in a longitudinal direction, from the vessel 14 and the heads 98 of the studs 94 are received in the recesses 100 of the closure plate 86. This inhibits the door 18 inadvertently opening during a sterilising cycle thereby improving the safety of the system 10. It will further be appreciated that, in use, the door 18 cannot be unlocked until the steam has been expelled from the chamber 24 of the vessel 14 and the chamber 24 is evacuated so that the door 18 is, initially, drawn inwardly causing the heads 98 of the studs 94 to clear the recesses 100 and allowing the closure plate 86 to be rotated to its open position.

Another problem which the applicant has identified with autoclaves is that, often, on completion of a sterilising cycle, a receptacle containing the instruments to be sterilised is wet resulting in problems handling the instruments and the danger of the instruments slipping out of one's grasp and falling on an unsterilised surface negating the sterilising operation just carried out on those instruments. Also, regulations normally require that, where a bag of sterilised instruments is to be stored, it must be dry before the door of the sterilising equipment is opened. The reason for this is that, if the bag is stored in a wet or damp condition, bacteria can migrate through the pores of the bag rendering the instruments unsafe for use.

Figure 5 illustrates a schematic air supply circuit of the system 10 for use in accordance with a method, in accordance with an embodiment of a fifth aspect of the invention, for drying items in the system 10.

Air from the air reservoir 44 is fed through sterile filters 102 in an air line 104.

The air line 104 branches, via a branch line 108, to the heat sink 20 and also, via a branch line 112, to the chamber 24 of the vessel 14. A hot air solenoid valve 106 is mounted in the branch line 108 while a cold air solenoid valve 110 is mounted in the branch line 112. It is to be noted that air is admitted half way up the chamber 24 at about a 3 o'clock or 9 o'clock position.

A low pressure side 42.1 of the air pump 42 communicates with the chamber 24 of the vessel 14 via a vacuum solenoid valve 114 mounted in a line 116. A high pressure side 42. 2 of the air pump 42 communicates with an inlet to the air reservoir 44. An air inlet valve 118 is connected to the air pump 42.

An exhaust valve 120 communicates with an exhaust port 122 of the vessel 14 through which waste water is ejected from the chamber 24 of the vessel 14 to a waste line 124.

It is to be noted from Figure 5 of the drawings that, firstly, the vessel 14 is tilted slightly downwardly towards its exhaust port 122 to facilitate ejection of water from the chamber 24. Secondly, the feed line 22 from the heat sink 20 feeds to a steam manifold 126 which runs along the top of the chamber 24 of the vessel 14.

In the drying of an item, being a basket or a bag containing instruments, mounted on the carriage 48 of the door 18 of the system 10, upon completion of a sterilising cycle, steam 72 needs to be purged from the chamber 24 of the vessel 14.

This is achieved by opening the exhaust valve 120 for approximately two seconds.

Cold air is passed through the solenoid valve 110 into the chamber 24 for approximately four seconds to condense steam within the chamber 24. The solenoid valve 106 is opened to introduce hot air into the chamber 24 to purge the chamber 24 of moisture through the exhaust valve 120. The chamber 24 is evacuated to a pressure of approximately-50kPa.

The above steps are carried out regardless of whether a flash (wet) sterilising cycle or a drying sterilising cycle is being done. If it is a flash cycle, the door 18 is opened after the above steps to allow the items to be removed.

To achieve dry bags or baskets, a further cycling through the above steps takes place. Initially, the chamber 24 is further evacuated to a pressure of approximately- 55kPa or less and the system 10 is then paused for approximately twenty seconds. The pressure in the chamber 24 of the vessel 14 is further lowered to approximately-70kPa with a further pause of about twenty seconds. These pauses allow for evaporation of moisture.

During these pauses, the air pump 42 runs with its ports open to allow it to cool.

The solenoid valve 110 is opened to facilitate cold dry sterile air exchange. This fills the chamber 24 with cold air at a low pressure which causes moisture condensation. The vacuum valve 114 is open and the pump 42 is running. This occurs for approximately four seconds.

All lines are then purged by filling the chamber with hot air via the opening of the valve 106 and supplying hot, sterile air heated by the heat sink 20. In this regard, it

will be noted that the immediate availability of hot air is a major advantage of the present system 10 in comparison with other systems of which the Applicant is aware.

This fills the chamber 24 with hot air under low pressure and forces condensed water out through the exhaust port 122 and exhaust valve 120. The air pump 42 is on and pulses approximately four pulses of hot dry air through the valve 106.

The interior of the chamber 24 is then again evacuated to approximately-70kPa to further cause evaporation of moisture on the instruments and/or basket containing the instruments whereafter the system 10 is paused for approximately twenty seconds.

After the pause, cold sterile air is fed into the chamber 24 via the valve 110 being open for approximately four seconds and then a further pause of four seconds occurs to cause further condensation.

After the pause, all the lines are purged by the injection of hot air into the chamber 24 by closing the valve 110 and opening the valve 106. Four pulses of hot dry air are injected into the chamber 24 through the heat sink 20 with the exhaust valve 120 being open to force further condensed water out through the exhaust port 122 to the waste line 124. The replacement of moist air by warm dry air also serves to aid evaporation of water on the instruments and bags.

The pressure in the chamber 24 is then lowered to approximately followed by a pause of approximately twenty seconds'duration.

The solenoid valve 110 is opened allowing cold dry air into the chamber 24 for approximately four seconds followed by a pause of four seconds. A final hot sterile air exchange occurs by closing the valve 110 and opening the valve 106 for approximately four seconds followed by a four second pause. This eliminates most condensed water from the chamber 24. The pressure in the chamber 24 is then brought to approximately -50kPa and the door 18 can be unlocked and its closure plate 86 rotated, as described above. A positive pressure is created in the chamber 24 to allow the door 18 to open using hot air from the heat sink 20.

The drying cycle will be slower if there is moisture in the system 10 as a sufficiently low negative pressure to effect drying will not be able to be achieved. To encourage moisture removal, the solenoid valves 114 between each vessel 14 and the low pressure side 42.1 of the pump 42 are angled downwardly, in use, to aid drainage.

Vapour, as it is removed from the chamber 24 of the vessel 14, is also directed downwardly as it enters a filter 128. The filter 128 acts as a condenser condensing the vapour. The liquid arising from condensation of the vapour is drained from the filter 128 through a downwardly angled exhaust line 130. At each pause in the evacuation stage of the drying cycle, compressed air is fed into the top of the filter 128 via a line

132 and the opening of a valve 134 in the line 132. This encourages the expulsion of water from the filter 128 into the exhaust line 130. via a check valve to inhibit back flow during the evacuation process. The water is inhibited from entering the pump 42 by closure of valves (not shown) on the high pressure side 42. 2 of the pump 42 and because the purging air is introduced between the pump 42 and the filter 128. This aids in the rapid removal of moisture from the system 10.

It is also to be noted that, where the reservoir 44 requires replenishment, air only is provided by the pump 42 to the reservoir 44. Any air plus moisture that is fed through the pump 42 during a drying cycle is exhausted upstream of the reservoir 44 to inhibit vapour being fed into the reservoir 44.

If one knows that the bag is dry, the drying process is able to be terminated more quickly thereby reducing time wastage. This can be achieved by monitoring the pressure in the chamber since. If moisture is present in the chamber 24 of the vessel 14 then, as vapour forms the pressure in the chamber 24 will increase. By monitoring this pressure level, if it remains stable for a predetermined period of time it can reasonably safely be assumed that the bag is dry and that the drying cycle can be terminate. For example, at the final evacuation stage, the pressure may be reduced to-83kPa. If the pressure remains within about 5kPa of this value for about 25 seconds, it may be assumed that the bag is dry and that the drying cycle can be terminated. The door 18 can then be opened and the bag removed.

Referring to Figures 6 and 7, two versions of heat sink 20 are iflustrated. The heat sink 20 of Figure 6 is intended for use in smaller systems 10 while the heat sink 20 of Figure 7 is intended for use in larger systems.

The heat sink 20 comprises a container 140 in which a heating element 142 is contained. A plurality of eatable bodies 144 such as metal spheres, rods, cubes or irregularly shaped elements are contained in the container 140 surrounding the heating element 142.

This has the effect of ensuring that all spare water is removed from the heat sink by steam pressure. Its advantage is that no further steam is produced once requirement is met and this of course is most important when door is opened.

In the heat sink of Figure 6, water to be vaporised is fed into the interior of the container 140 via a perforated tube 146. When the water is received in the interstices between the hot bodies 144, the water flashes off and becomes a vapour or steam. The steam is fed from the heat sink 20 to the vessel 14 via a perforated discharge tube 148.

The tube 146 is perforated along both sides to encourage an equal distribution of water in the top of the heat sink as the water is sprayed through the openings of the tube 146.

The discharge tube 148 is perforated along its bottom quadrant only, just above bottom dead centre of the tube 148. Preferably, the discharged tube 148 is arranged in abutment with an internal surface of the container 140 which aids heat transfer to fluid in the discharge tube 148. By having the perforations off bottom dead centre, the likelihood of the perforations being blocked by the wall of the container 140 is reduced.

Referring now to Figure 7 of the drawings, a variation of the heat sink 20 intended for larger systems is illustrated. With reference to Figure 6 of the drawings, like reference numerals refer to like parts unless otherwise specified.

In this embodiment, instead of the tubes 146 and 148, one continuous conduit 150 extends through the interior of the container 140. The conduit 150 follows a tortuous path through the interior of the container 140 to improve heat exchange between the water in the conduit 150 and the bodies 144 in the container 140. In this variation, in addition to the bodies 144, a heat exchange fluid in the form of oil is contained in the interior of the container 140 to substantially immerse the bodies 144 in the oil.

The oil is received in the interstices between the bodies 144 and aids in heat transfer to the fluid being conveyed through the conduit 150. Because the oil is used, the bodies 144 can be more tightly packed and scrap copper disks are used. As the oil expands on being heated by the heating element 142, excess oil expelled from the interior of the container is received into the oil reservoir 34 of the system 10.

Use of the oil and the more tightly packed bodies 144 results in a more efficient heat sink 20 which renders it useful in larger systems. It will be appreciated that, because the water is maintained in the conduit 150, only the conduit 150 needs to be pressurised, rather than the entire container 140.

In use, the system 10 is switched on at the beginning of a normal working day and, once it has reached its operating temperatures, cycles at its set points ready for use.

As a result, when it is desired to sterilise instruments, this can be effected rapidly using the system 10 as steam to be used in the sterilising cycle can be generated by the heat sinks 20 in approximately seven seconds. A total sterilising cycle can occur in less than six minutes, excluding a drying cycle, as described above. The drying cycle adds a further 5 to 6 minutes to the total process. It is also a major advantage of the invention that, by positioning the heat sinks 20 between the vessels 14, major improvements in the convection flow of the oil 32 is achieved resulting in lower power consumption requirements of the heaters 38. This improves the operating efficiency of the system 10 as well as reducing the power consumption of the system 10 making the system more cost efficient to operate.

Another advantage of the invention is that, unlike existing autoclaves of which the Applicant is aware where a singly placed chamber heating element is usually used to maintain chamber temperature resulting in even pressure throughout the chamber but gives rise to areas of uneven temperature, the use of the oil in the gap of the vessel encourages convective flow resulting in an even temperature throughout the vessel.

Yet a further advantage of the system 10 is that, with the door locking arrangement, the likelihood of the door working itself open during a sterilising cycle, is greatly reduced.

Yet a further advantage of the invention is that a drying cycle is provided which facilitates drying of bags or baskets containing instruments making it easier to remove the bags or baskets from the system 10, to handle the bags or baskets and, where applicable, to store the dried bags or baskets containing the instruments.

Still further, the provision of two vessels 14 allows greater flexibility as one vessel 14 is normally available for urgent use should it be required. For example, if an important piece of medical equipment is dropped and requires urgent sterilisation, this can be achieved by placing that instrument in one of the vessels 14 and effecting a flash drying cycle while a normal sterilising cycle is going on in the other vessel 14.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.