GB2074872A

GB2074872A - An autoclave

Info

Publication number: GB2074872A
Application number: GB8013807A
Authority: GB
Original assignee: FROUD D R A
Current assignee: FROUD D R A
Priority date: 1980-04-25
Filing date: 1980-04-25
Publication date: 1981-11-11
Also published as: ZA812643B

Abstract

An autoclave suitable for sterilising surgical and dental instruments has a pressure vessel 11 fitted with a door 15 which may be held closed by member 20 pivoted to the door and having three projecting arms 21 engageable behind abutments 18. A pressure-sensing bellows 29 expands on the internal pressure in the vessel 11 rising, to drive a lock pin 32 through an aperture provided in an arm 21a of the member 20, to prevent opening of the door. An electrically-operated solenoid valve 49 is arranged to be opened by a control timer after the interior of the vessel 11 has been at the required sterilising temperature for sufficiently long period, to allow rapid depressurisation of the vessel. Cooling of the vessel at that stage is assisted by a fan 55 which blows air thereover. A further lock pin 35 for the member 20 is withdrawn by a solenoid 37 only when the internal temperature in the vessel 11 is sufficiently low to allow safe opening of the door 15. <IMAGE>

Description

SPECIFICATION An autoclave This invention relates to an autoclave, and in particular but not exclusively to an autoclave intended for the sterilisation of various types of medical implements, such as dental instruments and tools, surgical instruments and so on.

It is common practice in the dental and medical fields to sterilise instruments by means of steam at a super-ambient pressure and a temperature in excess of 1000C. Such conditions require the use of a pressure vessel and an autoclave usually is employed for this purpose, adapted to cycle through a so-called "flash sterilisation" process in which the instruments are held to 1 360C for not less than 3 minutes, as laid down in a British Standard for sterilisation, but to obtain a more complete sterilisation, times of up to 6 minutes are often used. It has however been found that even by holding instruments for 6 minutes at 1360C, only 98% elimination of germs can be ensured.

Even though the instruments are held at the sterilisation temperature for at the most only 6 minutes, a typical cycle time for sterilisation is 20 to 25 minutes, in view firstly of the time required to bring the autoclave interior (and implements) up to the required 1360C and secondly of the time required subsequent to sterilisation for the temperature of the autoclave interior to fall to below 1000C and for the internal pressure to fall to approximately ambient pressure. It will be appreciated that the autoclave cannot safely be opened prior to the interior pressure falling to substantially atmospheric. The cooling time from the sterilisation temperature is somewhat protracted because the pressure vessel is of a relatively massive construction to ensure sufficient strength, and consequently has a high thermal capacity.Thus, should an instrument become contaminated, it is out of commission for some 20 to 25 minutes before it can be re-used, whilst the instrument is being sterilised.

Apart from the relatively long cycle times of the known sterilising autoclaves, another disadvantage is that the door mechanism has to be fitted with a highly reliable interlock arrangement, to prevent the door being opened when there is a super-ambient pressure within the autoclave. Such mechanisms have in the past tended to be either extremely bulky, complex and hence expensive, or barely sufficient and reliable enough for constant use whilst still affording great operator safety.

Yet another disadvantage of many known sterilising autoclaves is that only water of high purity may be used for the sterilisation itself. This is because the interior of the autoclave must be vented to atmosphere by means of a relatively small bleed orifice to prevent excessive pressure build-up within the autoclave, and if water not of high purity is used, the bleed orifice rapidly tends to become blocked. It is usual therefore to fit the autoclave with a condensor arrangement, so that steam venting through the bleed orifice as well as any steam issuing through a pressure relief valve is condensed and can be returned to the interior of the autoclave. Consequently, such an autoclave does not lend itself to field use, because the bulk and complexity make the autoclave difficult to transport.

It is a principle aim of this invention to provide an autoclave suitable for the sterilisation of medical instruments, which autoclave at least reduces some of the disadvantages mentioned above of known autoclaves.

According to one aspect of this invention, there is provided an autoclave comprising a pressure vessel having a closable door, means to raise the temperature within the pressure vessel, lock means for the door which lock means serves to prevent opening of the door once closed when at least one of the internal temperature and pressure is above a pre-set threshold value, and electricallyoperated solenoid valve having an inlet connected to the interior of the pressure vessel and an outlet which vents to atmosphere, and a control system for the valve which operates to open the valve after the interior of the pressure vessel has been maintained at a predetermined temperature for a preset time, thereby then to cause rapid depressurisation of the pressure vessel.

In a preferred embodiment of this invention, there is provided a fan adapted to drive air over the exterior of the pressure vessel once the interior of the vessel has been held at the predetermined temperature for the preset time, in order to assist the dissipation of heat from the vessel.

The autoclave of this invention allows relatively fast sterilisation cycles, as compared to the known designs of autoclave discussed above. This is because the solenoid valve is opened after the interior of the autoclave has been held at the required temperature for the preset time, thereby venting the excess pressure to atmosphere. The superheated steam thus released reduces considerably the total thermal energy of the autoclave, and hence reduces the amount of heat which otherwise would have to be dissipated prior to the temperature falling to a safe level. The rate of loss of such temperature can however further be assisted by means of the fan, which should be controlled to operate at the end of the preset sterilisation time.

The solenoid valve preferably has a movable valve member spring-biased to engage a valve seat and movable away therefrom on energisation of the solenoid, the co-operating surfaces of the member and seat advantageously being shaped so as to define, when engaged with each other, a relatively small bleed orifice therebetween. In this way, the solenoid valve may perform the function of providing the required bleed orifice, as well as serving as a pressure-venting valve. The valve member of the solenoid valve may be generally conical and engage a circular opening in a valve seat, in which case the bleed orifice can be defined by one ore more flats formed on the conical surface of the valve member.By providing the bleed orifice between the valve member and the valve seat, any tendency for the bleed orifice to become blocked is largely eliminated, for the steam issuing through the solenoid valve on the opening thereof to allow venting has a purging effect, cleaning any foreign matter from the cooperating surfaces.

In addition to the solenoid valve, the autoclave should be fitted with an emergency safety pressure relief valve, set to open at a pressure somewhat in excess of that which normally will be encountered in ordinary use.

As has been mentioned above, the provision of interlocks on the door of an autoclave is most important for operator safety. It is preferred for the lock means of the autoclave of this invention to include a pressure-sensing mechanism for the interior of the pressure vessel and directly operating a lock to prevent the door being opened once the pressure within the vessel has risen above a preset threshold. For example, the pressure sensing mechanism may be in the form of a bellows which expands as the pressure within the vessel rises, the expanding movement being coupled to a lock member which is moved to a position in which the member inhibits opening of the door.

In a similar way, an electrical temperature sensing element preferably is provided to sense the temperature of steam within the vessel, and there is a further lock member spring urged to a position in which the member inhibits opening of the door, the further lock member being movable away from that position by a solenoid which is energised only when the temperature sensed by said sensing element is below a safe value for instance, below 950C.

The closable door and lock means therefor must be arranged so as to be capable of closing the opening to the pressure vessel in a pressuretight manner, despite repeated operations and the arduous high-temperature conditions, but also must serve reliably to lock the door once closed, when the pressure or temperature rise above threshold values.These demanding requirements can be met by providing a generally cylindrical pressure vessel closed at one end and having a circular opening at the other end, a circular door for the opening, a sealing member disposed to effect a seal between the door and the pressure vessel around the opening when the door closes the opening, and a securing member pivoted to the door for movement about an axis substantially co-axial with the door, the securing member having at least two generally-radially extending arms which project beyond the periphery of the door and which arms may be engaged with corresponding ramp surfaces provided on abutment elements upstanding from the pressure vessel around the opening thereto, the lock means acting on the securing member when the arms thereof are engaged with the ramp surfaces.

Preferably, the securing member has three equi-spaced arms each of which is engageable with a corresponding abutment element having a ramp surface. In this way, by fitting the door over the opening and then turning the securing member to engage the arms with the ramp surfaces of the abutment elements, the door may tightly be held closed, and in view of the ramp surfaces, the further the securing member is turned, the greater the sealing effect. Turning of the securing member.

about the axis of the door can simply be achieved by providing a pair of stubs upstanding from the door parallel to the axis thereof, one to each side of an arm, and providing a key having a cylindrical outer surface and an internal eccentric bore in which may be received either of the stubs, whereby turning the key when fitted on a stub with the outer surface engaged with an arm moves that arm nearer the other stub. The key or stubs can be made to have only a limited strength, thereby to prevent forcing of the lock means when serving to hold the door closed, the key or stubs failing before the lock means.

With a door and securing member arranged as just-described, the lock means most effectively operates directly on the arms of the securing member to prevent turning thereof once a sterilisation sequence has started. For a case where two lock members are provided, one associated with a pressure sensing mechanism and the other associated with a temperature sensing element, it is preferred for each lock member also to be associated with one abutment respectively and to comprise a pin or bolt which may pass through an aperture provided in an arm of the securing member once the arm has been engaged with the ramp surface of an associated abutment element.In this way, when the securing member has been turned so the arms engage the abutment elements, the securing member may be locked by the lock members against release from the abutment elements until such time as both lock members are withdrawn from the arms.

It is preferred for the control system of the autoclave of this invention to provide comprehensive control functions which ensure both proper and safe operation of the autoclave.

The means to raise the temperature within the pressure vessel normally is an electric heater, and the control system should control the supply of power to the heater to inhibit the supply of power thereto until such time as the door has properly been closed. Conveniently, this may be achieved by providing a switch operable by the lock means, so as to prevent the heater being energised until the door is closed and properly locked.

The control system preferably includes a timer, which commences the timing of a sterilisation period once the temperature within the pressure vessel has reached a preset minimum value and normally 1 360C. The temperature sensing element for the door lock means may also serve to cause triggering of the timer, and at the end of the preset period, the timer should give an output which serves to open the solenoid valve, thereby depressurising the pressure vessel and allowing the pressure sensing mechanism to release the door lock means. Then, as soon as the temperature has fallen below 950C, the lock means is fully released, to allow opening of the door.

For the case where there is a temperaturecontrolled lock member for the door, the control system preferably controls the supply of power to the solenoid which pulls the lock member to release the door. For this purpose, the control system should sense the temperature and only when the temperature is below a predetermined threshold value - and typically 950C - should the solenoid be energised. Moreoever, a thermostatic control of the supply of power to the heating element should sense the temperature within the pressure vessel, and control the power accordingly so the temperature is maintained at substantially the predetermined value for the sterilisation period.However, it is preferred for the control system also allow sufficient power to be supplied to the heater so as to enable the interior of the pressure vessel to be held at some chosen value lower than the sterilising temperature. For example, such a value may be 800 C, so that the autoclave may operate in a "stand-by" mode, preheated ready for a sterilisation cycle. In this way, the sterilisation cycle time may further be reduced, because of the elimination of the initial warming up time, from the ambient temperature to the chosen "hold" temperature of typically 800C.

By way of example only, one specific embodiment of autoclave intended for the sterilisation of surgical and/or dental instruments and tools and arranged in accordance with this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a side view, but partly in section, of the embodiment of autoclave; Figure 2 is an end view of the autoclave of Figure 1; Figures 3a and 3b are respectively end and side views of the key for opening and closing the door of the autoclave; Figure 4 is a sectional view on an enlarged scale of the solenoid valve employed in the autoclave of Figures 1 and 2; Figures 5a and 5b are two views of the valve member of the solenoid valve of Figure 4; and Figure 6 is a block diagram of the control arrangement for the autoclave.

Referring initially to Figures 1 and 2, the autoclave of this invention comprises a housing 10 in which is mounted a pressure vessel 11 of generally cylindrical shape, end 12 of the vessel being closed and end 13 being provided with a circular opening 14 which may be closed by means of a door 1 5. A hinge 1 6 connects the door 15 to the housing 10, so that the door may be swung towards and away from a position in which it closes the opening 1 4. Attached to a flange affixed around the open end of the vessel 11 are three equispaced abutments 18, each providing a ramp surface 1 9 generally facing the front wall 1 7 of the housing 10.A securing member 20 is pivoted centrally on the door 15, the securing member 20 having three equi-spaced, radiallyextending arms 21 each of which projects beyond the periphery of the door 1 5 and may be engaged with the ramp surface 1 9 of one abutment 18 respectively. Once the door 1 5 has been closed, the securing member may be moved to engage the arms 21 with the abutments 1 8 by means of a key 23, shown in Figures 3a and 3b. The door 1 5 is provided with two stubs 22 upstanding from the front face thereof, one to each side of an arm 21.

The key 23 has a cylindrical outer surface 24 and a bore 25 eccentric with the outer surface 24, so that the key may be fitted on the stub 22. The key includes a boss 26, from which projects a pair of handles 27, to allow rotation of the key, such rotation causing the surface 24 to drive the adjacent arm 21 nearer the other stub. By virtue of the ramp surfaces 19, the further the rotation of the securing member 20, the greater the sealing pressure. The sealing effect is enhanced by means of an annular seal (not shown) disposed around the opening 14.

The pressure vessel 11 is provided with a pressure tapping 28, connected to a bellows 29 which expands upon the pressure within the vessel 11 rising. The bellows 29 has an operating rod 30 connected to a lever 31 which may move a pin 32 slidably mounted in abutment 1 8a against the action of a spring 33 upon expansion of the bellows 29, towards the adjacent ramp surface.

Thus, when the securing member 20 has been moved to a position in which the door 1 5 is held closed, the pin 32 may pass through an aperture 34 provided adjacent the end of the arm 21 a.

In a similar way, abutment 1 8b slidably carries a pin 35 which may pass through an aperture 36 in arm 21 b, the pin 35 being urged by a spring (not shown) to the right (in Figure 1) but being capable of being held away from that position by means of a solenoid 37. The armature 38 of the solenoid 37 projects towards a micro-switch 39, which switch is actuated whenever the pin 35 is withdrawn on energisation of the solenoid 37.

The pressure tapping 28 also connects to a safety valve 40, which may vent to atmosphere through duct 41 upon release thereof, and a pressure gauge 42 mounted on the front wall 1 7 is connected to the tapping 28 through a capillary pipe 42. A further pressure tapping 44 leads directly to a thermistor 45 and then to a steam chest 46. A pipe 47 connects the steam chest 46 to the inlet port 48 of a solenoid valve 49, the valve 49 having an outlet port 50 which vents to atmosphere. A further capillary pipe 51 leads from a temperature sensor in the steam chest to a temperature gauge 52, also mounted on the front wall 17 of the housing 10.

Around the lower external wall of the pressure vessel 11 , there is provided an electric heater 53, and a platform 54 is affixed within the vessel to serve as a carrier for tools to be sterilised. An electric fan 55 is mounted on a side face of the housing 10, to draw or blow air over the pressure vessel 11, when operated.

Figures 4, 5a and 5b show the solenoid valve 49 in greater detail. This valve includes a valve body 60 in which is slideably mounted a valve member 61 biassed by a spring 62 to engage a circular aperture in a valve seat 63, threaded in the valve body 60. A solenoid winding 64 surrounds the valve member and when energised draws the valve member 61 away from the seat 63, against the action of the spring 62 and any internal pressure within the vessel 11. The inlet port 48 communicates with the space surrounding the valve member 61 above the seat 63, and, when the valve member 61 is moved away from the seat 63, the inlet port communicates through the valve seat 63 with the outlet port 50.As can be seen in Figures 5a and 5b, the free end of the valve member 61 which engages the seat 63 is conical, but is provided with a pair of flats 65 on the conical portion 66 of the valve member, which flats together with the circular seat 63 define a bleed orifice even when the valve member is in the closed position, shown in Figure 4.

The autoclave described above is provided with a control system shown in block form in Figure 6.

This control system is centred around a door lock control,70, which serves to energise or de-energise the solenoid 37, thereby to allow opening of the door 15 only if the temperature within the pressure vessel is below approximately 950C. For this purpose, the control 70 receives a signal from the thermistor temperature sensor 45. The door lock control moreover inhibits the operation of the heater 53 of the pressure vessel 11, by the action of switch 39; whenever the solenoid 37 is energised to allow opening of the door. The temperature control 72 also serves to control the supply of power to the heater 53, dependent upon the sensed temperature.

The control system includes a timer 71 adjusted to time a period of typically 3 minutes once enabled by a signal from a temperature control 72, operating on the output of the thermistor 45. The timer provides a signal on line 73 to prevent the door lock control 70 allowing opening of the door once timing of a 3-minute period has started, until the end of that period. The timer 71 moreover controls the operation of the solenoid valve 49, causing the solenoid valve to open at the end of a 3-minute timing period. At the same time, the fan 59 is energised, to draw or blow air over the surface of the pressure vessel 11.

It will be appreciated that the autoclave described above is suitable for the sterilisation of surgical or dental tools and instruments, and allows a short cycle time for a sterilisation period of typically 1 360C for 3 minutes. This is because at the end of the sterilisation period the pressure vassel 11 is rapidly depressurised by opening of the solenoid valve 49, venting excess pressure to atmosphere, and moreover the fan 59 is energised to draw air over the pressure vessel 11 to increase the dissipation of heat from the vessel. The door, once closed, cannot be opened whenever either the temperature is above the chosen 'value of approximately 950C or the pressure is above atmospheric pressure by more than a small value of typically 14 mPa (approximately 2 p.s.i.g.) as determined by the pressure-sensing bellows mechanism 29.The autoclave may thus be operated with a high degree of safety.

In addition to the foregoing features, the control system may be arranged to allow the interior of the pressure vessel to be held at a preset temperature lower than 1000C, so that the autoclave may be maintained in a "stand-by" mode. For example, a suitable temperature may be 800 C, which is not too high to prevent opening and closing of the door with safety, and yet reduces the sterilisation cycle time, because the time required to raise the pressure vessel from the ambient temperature to 800C is eliminated.

In use, a small amount of water -- which need not be sterile or of high purity - is poured in the bottom of the pressure vessel, the door 1 5 is closed, and the power turned on. Provided that either a stand-by mode or steriiisation cycle is selected, the solenoid 37 is de-energised, operating switch 39 and allowing the supply of power to the heater 53. The door cannot now be opened, until solenoid 37 is energised once more, cutting power to the heater 53, If a stand-by mode is selected, the temperature control raises the internal temperature to 800C and holds it at that value, but otherwise the heater 53 raises the temperature to 1360C, whereat the timer 71 is triggered. As the temperature rises, the pressure within the vessel does so also, and after a rise of typically 14 mPa (Approximately 2 p.s.i.g.), the pin 32 of the pressure sensing mechanism serves to lock the door against release, not withstanding energisation of the solenoid 37.

At the end of a 3 minute timed period, the fan 55 is energised, and the solenoid valve 49 opened. The pressure within the vessel falls, withdrawing pin 32, and after the temperature has fallen to a safe value, the solenoid 37 may be energised to allow the door to be opened, and sterilised tools and instruments removed.

Claims

1. An autoclave comprising a pressure vessel having a closable door, means to raise the temperature within the pressure vessel, lock means for the door which lock means serves to prevent opening of the door once closed when at least one of the internal temperature and pressure is above a pre-set threshold value, and electricallyoperated solenoid valve having an inlet connected to the interior of the pressure vessel and an outlet which vents to atmosphere, and a control system for the valve which operates to open the valve after the interior of the pressure vessel has been maintained at a predetermined temperature for a preset time, thereby then to cause rapid depressurisation of the pressure vessel.

2. An autoclave as claimed in claim 1, wherein there is provided a fan adapted to drive air over the exterior of the pressure vessel once the interior of the vessel has been held at the predetermined temperature for the preset time, in order to assist the dissipation of heat from the vessel.

3. An autoclave as claimed in claim 1 or claim 2, wherein the solenoid valve has a movable valve member spring-biased to engage a valve seat and movable away therefrom on energisation of the solenoid.

4. An autoclave as claimed in claim 3, wherein the co-operating surfaces of the valve member and valve seat are shaped so as to define, when engaged with each other, a relatively small bleed orifice therebetween.

5. An autoclave as claimed in claim 4, wherein the valve member has a generally conical form and engages a circular opening in a valve seat, the bleed orifice being defined by one or more flats formed on the conical surface of the valve member.

6. An autoclave as claimed in any of the preceding claims, wherein the lock means includes a pressure-sensing mechanism for the interior of the pressure vessel which mechanism directly operates a lock to prevent the door being opened once the pressure within the vessel has risen above a preset threshold.

7. An autoclave as claimed in claim 6, wherein the pressure sensing mechanism is in the form of a bellows which expands as the pressure within the vessel rises, the expanding movement being coupled to a lock member which is moved to a position in which the member inhibits opening of the door.

8. An autoclave as claimed in any of the preceding claims, wherein an electrical temperature sensing element is provided to sense the temperature of steam within the vessel, and there is a further lock member spring urged to a position in which the member inhibits opening of the door, the further lock member being movable away from that position by a solenoid which is energised only when the temperature sensed by said sensing element is below a safe value.

9. An autoclave as claimed in any of the preceding claims, wherein the pressure vessel is generally cylindrical and is closed at one end and has a circular opening at the other end, there being a circular door for the opening, a sealing member disposed to effect a seal between the door and the pressure vessel around the opening when the door closes the opening, and a securing member being pivoted to the door for movement about an axis substatially co-axial with the door, the securing member having at least two generally-radially extending arms which project beyond the periphery of the door and which arms may be engaged with corresponding ramp surfaces provided on abutment elements upstanding from the pressure vessel around the opening thereto, the lock means acting on the securing member when the arms thereof are engaged with the ramp surfaces.

10. An autoclave as claimed in claim 9, wherein the securing member has three equi-spaced arms each of which is engageable with a corresponding abutment element having a ramp surface.

11. An autoclave as claimed in claim 10, wherein a pair of stubs upstand from the door parallel to the axis thereof, one to each side of an arm of the securing member, a key being provided which has a cylindrical outer surface and an internal eccentric bore in which may be received either of the stubs, whereby turning the key when fitted on a stub with the outer surface engaged with an arm moves that arm nearer the other stub.

12. An autoclave as claimed in any of claims 9 to 11, wherein the lock means operates directly on the arms of the securing member to prevent turning thereof once a sterilisation sequence has started.

13. An autoclave as claimed in claim 12, and in which two lock members are provided, one associated with a pressure sensing mechanism and the other associated with a temperature sensing element, wherein each lock member also is associated with one abutment element respectively and comprises a pin or bolt which may pass through an aperture provided in an arm of the securing member once the arm has been engaged with the ramp surface of an associated abutment element.

14. An autoclave as claimed in any of the preceding claims, wherein the control system includes a timer which commences the timing of a sterilisation period once the temperature within the pressure vessel has reached a preset minimum value.

1 5. An autoclave as claimed in claim 14, wherein the timer gives an output which serves to open the solenoid valve at the end of the preset period, thereby depressurising the pressure vessel.

1 6. An autoclave as claimed in any of the - preceding claims, wherein the control system is arranged to allow sufficient power to be supplied to the heater so as to enable the interior of the pressure vessel to be held at some chosen value lower than the sterilising temperature until a sterilising sequence is commenced.

1 7. An autoclave substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. An autoclave as claimed in any of the preceding claims, wherein a switch is disposed so as to be operable by the lock means, which switch serves to prevent the heater being energised until the door is closed and properly locked.

1 5. An autoclave as claimed in any of the preceding claims, wherein the control system includes a timer which commences the timing of a sterilization period once the temperature within the pressure vessel has reached a preset minimum value.

16. An autoclave as claimed in claim 15, wherein the timer gives an output which serves to open the solenoid valve at the end of the preset period, thereby depressurising the pressure vessel.

1 7. An autoclave as claimed in any of the preceding claims, wherein the control system is arranged to allow sufficient power to be supplied to the heater so as to enable the interior of the pressure vessel to be held at some chosen value lower than the sterilizing temperature until a sterlising sequence is commenced.

1 8. An autoclave substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

New claims or amendments to claims filed on 24.4.81.

Superseded claims ALL claims 1-18 New or amended claims:

1. An autoclave comprising a pressure vessel having a closable door, means to raise the temperature within the pressure vessel, lock means for the door which lock means includes a pressure-sensing mechanism for the interior of the pressure vessel and which mechanism directly operates a lock to prevent opening of the door once closed when the sensed pressure within the vessel has risen above a preset threshold value, an electrically operated solenoid valve having an inlet connected to the interior of the pressure vessel and an outlet which bents to atmosphere, and a control system for the valve which operates to open the valve after the interior of the pressure vessel has been maintained at a predetermined temperature for a preset time, thereby then to cause rapid depressurisation of the pressure vessel.

6. An autoclave as claimed in claim 1 wherein the pressure sensing mechanism is in the form of a bellows which expands as the pressure within the vessel rises, the expanding movement being coupled to a lock member which is moved to a position in which the member inhibits opening of the door.

7. An autoclave as claimed in any of the preceding claims, wherein an electrical temperature sensing element is provided to sense the temperature of steam within the pressure vessel, and there is a further lock member spring urged to a position in which the member inhibits opening of the door, the further lock member being movable away from that position by a solenoid which is energised only when the temperature sensed by said sensing element is below a safe value.

8. An autoclave as claimed in any of the preceding claims, wherein the pressure vessel is generally cylindrical and is closed at one end and has a circular opening at the other end, there being a circular door for the opening, a sealing member disposed to effect a seal between the door and the pressure vessel around the opening when the door closes the opening, and a securing member being pivoted to the door for movement about an axis substantially co-axial with the door, the securing member having at least two generally extending arms which project beyond the periphery of the door and which arms may be engaged with corresponding ramp surfaces provided on abutment elements upstanding from the pressure vessel around the opening thereto, the lock means acting on the securing member when the arms thereof are engaged with the ramp surfaces.

9. An autoclave as claimed in claim 8, wherein the securing member has three equi-spaced arms each of which is engageable with a corresponding abutment element having a ramp surface.

10. An autoclave as claimed in claim 9, wherein a pair of stubs upstand from the door parallel to the axis thereof, one to each side of an arm of the securing member, a key being provided which has a cylindricat outer surface and an internal eccentric bore in which may be received either of the stubs, whereby turning the key when fitted on a stub with the outer surface engaged with an arm moves that ram nearer the other stub.

11. An autoclave as claimed in any of claims 8 to 10, wherein the lock means operates directly on the arms of the securing member to prevent turning thereof once a sterilisation sequence has started.

12. An autoclave as claimed in claim 11, and in which two lock members are provided, one associated with a pressure sensing mechanism -and the other associated with a temperature sensing element, wherein each lock member also is associated with one abutment element respectively and comprises a pin or bolt which may pass through an aperture provided in an arm of the securing member once the arm has been engaged with the ramp surface of an associated abutment element.

13. An autoclave as claimed in any of the preceding claims, wherein a switch is disposed so as to be operable by the lock means, which switch serves to prevent the heater being energised until the door is closed and properly locked.