GB2131695A - Sterilising autoclaves - Google Patents

Abstract

An autoclave operating alternately with steam under pressure and vacuum for sterilizing articles wherein water is caused to circulate in a closed circuit comprising a water tank (2), an autoclave chamber (1), a steam generator (8), a water pump (3), and a suction pump (5), the suction pump is a water jet pump supplied with water, as motive fluid, from the tank (2) by the pump (3), the sterilisation process is controlled by means of the pump (3), a two-way controlled valve (13) and a three-way controlled valve (10), with non-return valves (12, 16) automatically supplementing the controlled valves. <IMAGE>

Description

SPECIFICATION Method of sterilising articles in an autoclave and an autoclave for performing the method The present invention relates to a method of sterilising articles in an autoclave using steam under pressure and vacuum alternately, in which method the air in the autoclave chamber is removed, steam under pressure is introduced into the chamber to act over the period necessary to effect sterilisation, and the chamber is subsequently evacuated to dry the articles being sterilised, whereafter the autoclave chamber is restored to atmospheric pressure by admission of sterile air. The invention also relates to an autoclave for performing the method according to the invention.

Autoclaves used nowadays in hospitals and similar larger institutions, normally operate with alternating vacuum and steam under pressure.

These autoclaves are large, complicated and expensive. Furthermore, they do not operate with a closed system and the steam condensed is therefore allowed to pass straight out to the drainage system.

In smaller establishments such as dental surgeries with only one or a few dentists, the capacity of a large autoclave cannot be exploited and such a large autoclave would constitute too large an investment. Small autoclaves, of more or less sophisticated design, are available for such purposes.

When sterilising articles such as bandages and instruments, etc., the articles are treated with steam at a temperature exceeding 1000C. In its simplest form, sterilisation is simply performed by water being heated by means of elements in the autoclave chamber. Small autoclaves available today are able to apply steam under pressure to the autoclave chamber, but not to subject the autoclave chamber to partial vacuum. In these small autoclaves, pressurisation of the steam is achieved by providing an elevated water container, and providing solenoid valves and an electrical element arranged to generate steam of which the pressure varies in surges.

As requirements of hygiene increase, the demand for smaller autoclaves which are able also to apply vacuum in the autoclave chamber and which utilise a closed water system increases.

Large autoclaves cannot be made proportionally smaller and still function economically and reliably. The difficulties encountered in reducing the size are probably the main reason for there being no small vacuum autoclaves on the market.

It is among the objects of the invention to provide a method of vacuum-sterilising in autoclaves, and an autoclave permitting sterilisation, using steam under pressure and vacuum, but which are still suitable for use in dental surgeries, small doctor's surgeries, laboratories and so on, with a closed water system and at a reasonable cost.

In a method according to the invention, water is caused to circulate in a closed circuit, air being removed from the autoclave chamber by evacuation of the autoclave chamber, possibly after a preceding expulsion by steam, by means of a suction generated by a water jet pump (as herein defined), in the circuit, after which the circuit is broken between the outlet of the autoclave chamber and the rest of the circuit, and the connection between a water tank included in the system and a steam generator is simultaneously opened to pressurise the autoclave chamber with high-pressure steam for the actual sterilisation process, after which the autoclave chamber is again evacuated by re-opening the connection between the outlet of the autoclave chamber and the rest of circuit, and once a state of vacuum has been reached, maintaining this for the period necessary to effect drying, after which the connection between the outlet of the autoclave chamber and the rest of the circuit is again broken and a connection simultaneously opened to the surrounding atmosphere via a sterile filter to effect pressure equalisation with the atmosphere.

The term "water jet pump", as used herein refers to a suction pump for gases, such as air, in which water under pressure, as motive fluid, is led from an inlet to a chamber which it enters in the form of a jet or spray to exit from the chamber and pass to an outlet, entraining air or other gas supplied to said chamber via a third connection which functions as the suction inlet of the pump.

Such pumps are known perse and such a pump is herein referred to as being "as herein defined".

In one embodiment of the invention the air is removed continuously from the autoclave chamber, the chamber being simultaneously pressurised by means of high-pressure steam.

In another embodiment of the invention the steam leaving the autoclave chamber is cooled by means of a cooler arranged in a return pipe.

An autoclave for performing the method according to the invention is characterised by a closed water circuit comprising a water tank, a pump for pumping water to a steam generator for the supply of steam to the autoclave chamber, and for pumping water through an ejector and back to the water tank through a return pipe to generate a sub-pressure in order to lower the pressure and create a vacuum in the autoclave chamber by way of a pipe connected to the ejector and a pipe from the autoclave chamber via an adjustable valve to the atmosphere.

In an autoclave embodying the invention, an outlet pipe from the autoclave chamber may be connected to a three-way valve, which communicates both with a pipe, connected via a non-return valve and pipe to the water jet pump, and also with the pipe communicating with the atmosphere via a sterile filter.

The first-mentioned pump may be arranged to pump water through a pipe via the water jet pump to the steam generator, a two-way valve being arranged in the return pipe from the ejector to the water tank.

In another embodiment of the invention the first-mentioned pump may be in direct communication with the water jet pump via a first two-way valve and is also in direct communication with the steam generator via a second two-way valve.

In a still further embodiment of the invention means is arranged which, when all air has been removed from the pressure chamber, closes the outer circuit. Such means might be a thermostat actuating the three-way valve, or a by-pass pipe, by-passing the three-way valve and containing a steam trap.

A by-pass conduit with non-return valve may be arranged between a pipe leading from the three-way valve to the jet pump and the returnpipe leading back to the water tank.

A cooler may be arranged to cool the steam leaving the autoclave chamber. The cooler may be located in a pipe immediately downstream of the three-way valve, in the conduit by-passing the jet pump or in the pipe leading to the water tank.

Preferred embodiments of the autoclave function well without a cooler, when used only for occasional sterilisations, but if used repeatedly the water in the system will soon become too hot for the autoclave to function satisfactorily without a cooler.

In the embodiment with a two-way valve, a non-return valve is preferably arranged between the first-mentioned pump and the jet pump. Due to the pressure drop over the non-return valve, the tank may be located higher than the steam generator without risk of water running to the steam generator when the pump is not operating.

If there is no leakage from the pump when not in operation, this non-return valve may be omitted.

Such a non-return valve prevents steam from penetrating into the pump when this is stationary during the sterilisation phase.

Embodiments of the invention are described below by way of example with reference to the accompanying drawings in which: FIGURE 1 shows schematically one autoclave embodying the present invention, FIGURE 2 shows a second embodiment of the invention, and FIGURE 3 shows a modified form of the autoclave of Figure 1.

The autoclaves shown in the drawings thus are intended to be used in a preferred sterilisation process entailing removal of air from the autoclave chamber, pressurising the chamber by means of steam, generating a partial vacuum, in an initial evacuation stage, renewing pressurisation with steam and carrying out sterilisation, evacuating the chamber again for drying and finally returning the autoclave chamber to atmospheric pressure by allowing sterile air into the pressure or sterilising chamber.

The method can of course be varied without departing from the scope of the invention. For instance, the air may be directly evacuated from the autoclave chamber without preceding pressurisation with steam.

In Figure 1 the autoclave chamber or pressure chamber is designated 1 and a water tank 2.

A path for fluid flow leads from the water tank 2 via a water pump 3, and a pipe 4 to the water inlet of a water-jet pump, as herein defined, referenced 5. The suction inlet of jet pump 5 is connected, via pipes 6 and 7 with a steam generator 8 connected with the autoclave chamber 1. During steam pressurisation, water from the tank is pumped to the steam generator which supplies steam to the pressure chamber 1.

A path for fluid flow from the autoclave chamber extends through an outlet pipe 9, a three-way valve 1 0 and a pipe 11 which, via a non-return valve 12, communicates with the pipe 6, connected with the section inlet of suction pump 5. The outlet of the pump 5 is connected to the water tank 2 via a two-way valve 13 and pipe 14.

As will be appreciated from what follows, during a complete cycle of use of the autoclave, water passes from tank 2, via pump 3, pump 5, pipes 6 and 7 and steam generator 8 to chamber 1 and passes from steam generator 1 via pipe 9, valve 10, pipe 1 valve 12, and back through pipe 6 to pump 5, from whence it passes via valve 13 to the tank 2. This path for water flow may be regarded as an outer circuit, although it will be appreciated that the water does not flow continuously at a steady rate around this outer circuit, but, for example, at some times flows in one direction through pipe 6 and at other times in the opposite direction through pipe 6.

Furthermore, it will be appreciated that in some parts of this outer circuit water flows as a liquid, and in other parts the water flows as steam. What may be regarded as an inner circuit is also defined, extending from the water tank 2 via the pump 3 and pipe 4 through the pump 5, solenoid valve 13 connected to the outlet of pump 5 and thence, via pipe 14, back to the tank 2.

The autoclave also includes a sterile filter 1 5 which is in communication with the three-way valve 10 via a pipe 17 provided with a non-return valve 16. A safety valve 18 is also provided to prevent excessive pressure building up within the pressure chamber 1.

The two-way valves and three-way valve may be solenoid valves or pneumatically controlled valves, and the non-return valves are autocontrolled.

To supply steam to the autoclave chamber 1 the solenoid valve 13 is closed and water is then pumped, by pump 3, through the jet pump 5 to pass from the suction inlet thereof to the steam generator 8 which blows steam into the chamber 1. The three-way valve 10, during this phase, is placed in a position in which the pipe 9 is cut off from the pipe 11 and from the pipe 17, in order to allow steam pressure to build up in the pressure chamber. When a predetermined pressure has been reached, the pump 3 is stopped. During this phase, in order to maintain the pressure in chamber 1 at the desired value, this pressure is sensed continuously, and whenever the pressure drops below the desired value, the pump 3 is started for a moment to restore the pressure to the desired value.

In the next phase, to lower the pressure and evacuate the chamber 1 , the pipe 11 is placed in communication with pipe 9 by operation of the three-way valve 10. The two-way solenoid valve 13 is also opened so that the pump 3 now pumps water through the jet pump 5 to create a partial vacuum in pipe 6, and thus via non-return valve 12, pipe 1 valve 10 and pipe 9, in the chamber 1. The water pumped through pump 5 returns, via conduit 14, to tank 2.

When sterilising packed up goods, for instance, in order to remove most of the air in the autoclave chamber and in the wrappings before sterilisation, it is preferable to adopt a procedure in a first step of which steam is supplied under pressure to the autoclave chamber 1. A considerable amount of the air is thus forced out and in a second step, the chamber 1 is evacuated, by means of pump 5, until a partial vacuum exists in the chamber. The steam-air mixture present in the wrappings is thereby drawn out substantially entirely and extremely good evacuation is obtained. The chamber 1 is subsequently filled again with steam under pressure for sterilisation of the articles, after which it is evacuated again by means of pump 5, for drying of the articles.In the embodiment of the autoclave shown in Figure 1, air cannot be removed continuously during simultaneous pressurising and pressurisation and air removal are instead performed intermittently. However, simple modifications are possible to enable continuous pressurising while simultaneously removing the air, as will be described below.

In either of the methods described above with reference to Figure 1, when sterilisation and drying under subsequent partial vacuum have been completed, the pressure in chamber 1 must be equalised to atmospheric pressure. To this end, the three-way valve 10 is operated to place pipe 9 in communication with pipe 17 and the sterile filter 15, and sterile air flows into the chamber 1 through pipe 9. The non-return valve 16 prevents air from flowing to filter 1 5 from chamber 1 and pipe 9, should the three-way valve be operated to connect pipe 9 with pipe 17 when pressure above atmospheric prevails in the system.

Figure 2 shows another embodiment of the invention. The same references are used as in Figure 1 to denote the same parts. The arrangement of Figure 2 differs from that of Figure 1 in that a first two-way valve 19 is arranged in the pipe 4 upstream of the pump 5.

Furthermore, the downstream side of pump 3 is connected directly to the steam generator 8 via a second two-way valve 20.

This embodiment permits continuous removal of air from the chamber 1 while the chamber is simultaneously pressurised with steam. To this end, during the initial part of the phase in which steam under pressure is supplied to the chamber 1, the second two-way valve 20 is kept open and three-way valve 10 is kept in its position connecting pipe 9 with pipe 11, while the first two-way valve 19 is closed. The air flow out through the outlet pipe 9 of the autoclave chamber, via the three-way valve 10, through the ejector 5 and out into the tank 2 after passing along the pipe 14. When substantially all air has been removed, the three-way valve 10 is placed in its position cutting pipe 9 off from pipes 11 and 17 in order to build up pressure in the chamber 1.

This course of events can be controlled in a number of ways, such as those described in more detail in connection with Figure 3.

Once a predetermined pressure has been reached in the autoclave chamber, the second two-way valve 20 is closed and the first two-way valve 19 is opened and the valve 10 is placed in its position connecting pipe 9 with pipe 11. The steam is thus removed from the chamber and the chamber is evacuated by the suction generated in the suction pump 5. By this method, any air remaining in the wrappings, for instance, is removed and an extremely good evacuation result is obtained. Renewed pressurisation is then achieved by closing the first two-way valve 19, placing the three-way valve 10 in its position cutting off pipe 9 from pipes 11 and 17 and opening the second two-way valve 20.During the actual sterilisation phase the pressure is maintained by sensing the pressure in chamber 1 continuously and whenever the pressure sensed drops below the desired value, momentarily starting the pump and at the same time opening the second two-way valve 20. Subsequent evacuation is performed as described above in relation to the initial evacuation and the vacuum maintained for long enough to effect drying.

Pressure-equalisation to atmospheric pressure is performed as described with reference to Figure 1, both two-way valves 19 and 20 being closed in this phase and the three-way valve 10 being placed in its position connecting pipe 9 with the sterile filter 15.

Thus, in the embodiment of Figure 1 the autoclave is controlled by means of the single two-way valve, pump 3 and the three-way valve, whereas in the embodiment according to Figure 2 it is controlled by both two-way valves, pump 3 and the three-way valve. The non-return valves in the system are simple, reliable, inexpensive and, most important, they work entirely automatically.

The autoclaves described with reference to Figures 1 and 2 thus provide extremely simple control with only a few controlled valves, i.e. two or three, respectively. This should be compared with certain autoclaves on the market which require up to seven controlled valves.

Figure 3, showing a modified form of the embodiment of Figure 1, uses the same references as Figure 1 for the same parts.

The embodiment of Figure 3 differs from the embodiment of Figure 1 as follows:- A non-return valve 21 is arranged between the pump 3 and jet pump 5. Due to the fact that a certain pressure drop is necessary over this nonreturn valve, to open the same, the water tank 2 can be located higher than the steam generator 8, without risk of water running into the steam generator when the pump is stationary. A by-pass pipe 22 incorporating a steam-trap 23 also extends from pipe 9 to pipe 11, by-passing the three-way valve 10. By keeping the three-way valve 10 in its closed position during evacuation of the pressure chamber 1, the air is force to pass pipe 22 and steam-trap 23. When substantially all air has been forced out, the steam-trap will automatically break the outer circuit, thus providing simple, reliable and convenient control.

Alternatively a thermostat can be arranged in pipe 9 to close the three-way valve 10 when a certain temperature has been reached. In the embodiments shown in Figures 1 and 2 the removal of air may be discontinued either after a certain time or when a certain vacuum has been achieved.

In the embodiment of Figure 3 a second bypass pipe 24 is also provided extending from a connection with pipe 11 at a position between valve 10 and valve 12, to a connection with line 14 downstream of a two-way solenoid valve 13 which in turn is downstream of pump 5. The second by-pass pipe 24 thus by-passes the non return valve 12, pump 5 and two-way valve 13. A non-return valve 25 is also arranged in pipe 24.

This enables continuous evacuation and simultaneous pressurisation with steam. Another advantage is that lowering the pressure in the chamber 1 can be accomplished considerably quicker than if the entire flow were to pass through pump 5.

To permit frequent use of the autoclave, cooling must be provided somewhere in the system.

Figure 3 shows a cooler 26 arranged in pipe 24 downstream of non-return valve 25. Hot water and steam passing to the cooler 26 is thus cooled before passing through pipe 14 to water tank 2.

However, the cooler may alternatively be located in pipe 11, immediately downstream of three-way valve 10.

The advantage of the arrangement shown in Figure 3 is that the cooler need not be evacuated during the initial evacuation step prior to sterilisation nor during the evacuation step after sterilisation.

Apart from the non-return valve 21 disposed downstream of the pump 3, the described modifications of the system of Figure 1 incorporated in the system of Figure 3 can equally well be carried out to the embodiment of Figure 2.

Furthermore, it should be noted that these modifications can be carried out individually, collectively, or in various combinations.

The predetermined pressure of the steam within chamber 1 during sterilisation may appropriately be in the vicinity of 230 kPa and the steam temperature ca. 1350C. When the water or steam is cooled in the system a relatively good vacuum can be maintained in the pressure chamber even with frequent use. There is no problem in maintaining the vacuum of 20 mm Hg.

Additional modifications of the invention are of course possible within the scope of the following claims. For instance, heat-exchange may be effected between the water in pipe 7 upstream of the steam generator 8 and the cooler 26, in the arrangement of Figure 3. Atwo-way valve can also be arranged in pipe 7 between pipe 6 and steam generator 8, in the arrangements of Figures 1 and 3 so that the pump 3 can be stopped during the pressure-reducing phase. The three-way valve 10 might also be replaced by two two-way valves.

Claims (21)

1. A method of sterilising articles in an autoclave using steam under pressure and vacuum alternately, in which method the air in the autoclave chamber is removed, steam under pressure is introduced into the chamber to act over the period necessary to effect sterilisation, the chamber is then evacuated to dry the articles being sterilised and the autoclave chamber is finally restored to atmospheric pressure by admission of sterile air, the method including the steps of providing: a water tank with an outlet conduit; a pump operable to pump water from said tank along said outlet conduit, and a steam generator connected with the autoclave chamber, and in which method the air is removed from the autoclave chamber by means of a suction pump in the form of a water jet pump, as herein defined, of which the motive fluid inlet is connected with said outlet from the tank downstream of the firstmentioned pump, after which the steam generator is supplied with water, from the water pump, to supply steam under pressure to the autoclave, whilst the escape of air or steam from the autoclave, at least below a predetermined pressure in the autoclave, is prevented, after which the supply of water to the steam generator is terminated and the autoclave chamber is again evacuated by means of said suction pump and once a predetermined level of vacuum has been reached in the autoclave chamber, this level is maintained for the period necessary to effect drying, after which the outlet of the autoclave chamber is closed off from the suction pump and a connection simultaneously opened between the surrounding atmosphere and the autoclave chamber, via a sterile filter, to effect pressure equalisation with the atmosphere.

2. A method according to claim 1, in which the air is removed continuously from the autoclave chamber, whilst the chamber is being simultaneously pressurised with high-pressure steam.

3: A method according to claim 1, in which steam leaving the autoclave chamber is cooled before being returned to the water tank.

4. An autoclave for sterilising articles using steam under pressure and vacuum alternately, by a method in which the air in the autoclave chamber is removed, steam under pressure is introduced into the chamber to act over the period necessary to effect sterilisation, the chamber is then evacuated to dry the articles being sterilised and atmospheric pressure finally restored by admission of sterile air into the autoclave chamber, the apparatus including a steam generator connected with the autoclave chamber, a suction pump, in the form of a water jet pump, as herein defined, for evacuating the autoclave chamber, and a water circuit comprising a water tank, a pump for pumping water to the steam generator for the supply of steam to the autoclave chamber and for pumping water, as motive fluid, through the water jet pump and back to the water tank via a return pipe.

5. An autoclave according to claim 4, in which an outlet pipe from the autoclave chamber is connected to a three-way valve which in one position is closed, in another position connects said outlet pipe with a first pipe, connected, via a non-return valve, to the jet pump, and in yet another position connects said outlet pipe with the atmosphere.

6. An autoclave according to claim 5 wherein, in said yet other position, the three-way valve connects said outlet pipe with atmosphere via a sterile filter.

7. An autoclave according to claim 4, 5 or 6, in which the first-mentioned pump is arranged when supplying water to the steam generator to pump said water to the steam generator via said jet pump and in which a two-way valve is arranged in the return pipe from the jet pump to the water tank.

8. An autoclave according to claim 7, in which a non-return valve is also arranged in the conduit between the first-mentioned pump and the jet pump.

9. An autoclave according to claim 4, 5 or 6, in which the first-mentioned pump is in direct communication with the jet pump via a first twoway valve and is also in direct communication with the steam generator via a second two-way valve.

10. An autoclave according to claim 5, in which a thermostat is arranged in the outlet pipe from the autoclave chamber to control the three-way valve.

11. An autoclave according to claim 5, in which a by-pass conduit with a steam trap is arranged past the three-way valve.

1 2. An autoclave according to claim 5, in which a by-pass conduit with a further non-return valve extends from the connection between the threeway valve and the first-mentioned non-return valve to the return pipe leading from the jet pump back to the water tank.

13. An autoclave according to claim 5, in which a cooler is arranged in said first pipe extending from the three-way valve to the jet pump via the first-mentioned non-return valve.

14. An autoclave according to claim 12, in which a cooler is arranged downstream of the further non-return valve in the by-pass conduit leading between said first pipe and the return pipe to the water tank.

1 5. A method of sterilising articles, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

1 6. A method of sterilising articles, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

1 7. A method of sterilising articles, substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

1 8. An autoclave substantially as hereinbefore described with reference to, and as shown in Figure 1 of the accompanying drawings.

1 9. An autoclave substantially as hereinbefore described with reference to, and as shown in Figure 2 of the accompanying drawings.

20. An autoclave substantially as hereinbefore described with reference to, and as shown in Figure 3 of the accompanying drawings.

21. Any novel feature or combination of features described herein.