GB2164258A - Formaldehyde sterilizers - Google Patents

Abstract

A method of metering sterilent e.g. formaldehyde into a sterilizer comprises creating a vacuum in a chamber and opening that chamber to a source of sterilent whereby sterilent is drawn into the chamber by the vacuum. The chamber is closed to the source of sterilent when a predetermined pressure is reached such that a fixed metered amount of sterilent may be subsequently released to the sterilizer. Since a known fixed amount of sterilent is released, the concentration of sterilent in the sterilizer can be controlled to effect a maximum sterilizing efficiency with minimum contamination within the sterilizer.

Description

SPECIFICATION Improvements in and relating to sterilizers This invention relates to sterilizers and in particular a method of introducing sterilent into a sterilizer.

One type of known sterilizers are used to destroy both vegetative and sporing organisms in applications where heat sensitive items are to be sterilized. Typically temperatures below 70"C are used during the cycle. The organisms are destroyed by the action of, for example, both steam and formaldehyde vapour under sub-atmospheric conditions.

In particular, items to be sterilized are placed within a sterilizer chamber which is then sealed and evacuated to an air pressure typically below 50 m.bar. In known sterilizers, the method by which this vacuum is generated and air is removed varies, and may be assisted by the use of steam. Having attained a vacuum of the desired level the formaldehyde vapour is introduced into the chamber, shortly followed by an admission of steam. On reaching the required temperature the low pressure condition is re-established and the cycle can be further repeated.

Such sterilizers are, however, prone to the formation and deposit of paraformaldehydes since formaldehyde is introduced directly into the sterilizer in unmetered quantities.

In accordance with one aspect of the invention, a method of metering sterilent into a sterilizer comprises creating a vacuum or sub-atmospheric pressure within a chamber, opening a source of sterilent to the chamber such that sterilent is drawn therein by the vacuum, closing the source of sterilent to the chamber when a predetermined pressure in the chamber is reached, and releasing the consequently metered amount of sterilent from the chamber to a sterilizer.

Such a method accurately controls the amount of sterilent passed into the sterilizer.

Preferably, the metered amount of sterilent in a liquid state is released from the chamber firstly into an evaporator in which the sterilent is converted into a vapour prior to introduction into the sterilizer itself.

Suitably, steam is introduced into the sterilizer after the metered amount of sterilent is released into the sterilizer, so as to create a condition of maximum sterilizing effect. Advantageously, such steam may be introduced via the chamber and/or evaporator.

Prior to temporary shutting down of the sterilizer, steam may be passed through the chamber and/or evaporator in order to clean (purge) such components of any residue sterilent.

In accordance with another aspect of the invention, a sterilent metering apparatus for a sterilizer comprises a chamber in which a vacuum or sub-atmospheric pressure may be periodically created, first valve means to open and close the chamber from a source of sterilent, and second valve means between the chamber and the sterilizer.

In use and when connected to a sterilizer, the vacuum created in the sterilizer can be opened to the chamber by opening of the second valve means, the second valve means then being closed and the first valve means being opened so that the vacuum in the chamber acts to draw an amount of sterilent into the chamber, the volume of which is determined by the volume of the chamber. The first valve means is then closed and the second valve means opened to release a metered amount of sterilent from the chamber to the sterilizer.

Preferably the sterilent is released by the second valve means into an evaporator in which the sterilent in a liquid form is converted into a vapour prior to introduction into the sterilizer.

Suitably, third valve means are provided to open and close the chamber to a source of steam, whereby steam may be introduced into the chamber and subsequently via the second valve means into the sterilizer after the metered amount of sterilent is introduced into the sterilizer, in order to create a condition of maximum sterilizing effect. Such an arrangement may be used alternatively to clean (purge) the chamber, second valve means, and/or evaporator of any residue sterilent.

Suitably, the first and second valve means are either two separate valves or a single two-way valve. A non-return valve is preferably provided between the first valve means and the chamber as a safety feature in order to prevent steam passing to the source of sterilent.

Preferably, the sterilent is Formalin, a liquid sterilent which on evaporation is converted to a Formaldehyde vapour.

The method and apparatus in accordance with the invention accurately controls the amount of sterilent used in any one cycle in relation to the volume of the sterilizer, whereby a known concentration of sterilizing vapour is produced. This concentration can be controlled in order to effect a maximum sterilizing efficiency with minimum contamination within the sterilizer.

Such an arrangement is suitably used for the sterilizing (or aiding thereof) of items within the sterilizer, such as heat sensitive medical items-for example, exploratory equipment.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure lisa diagrammatic representation of one embodiment of metering apparatus in accordance with the invention together with a sterilizer, and Figure 2 is a diagrammatic representation of another embodiment of metering apparatus in accordance with the invention together with a sterilizer.

The system 10 shown in Figure 1 comprises a metering apparatus 14 and a sterilizer 12.

The metering apparatus 14 is composed of a chamber 16 surrounded by three valves 18, 20 and 22, a source of sterilent 24, a source of steam 26 and an evaporator (vapouriser) 28.

In each cycle operation, a vacuum or subatmospheric pressure is firstly created in the sterilizer 12 which is realised in the evaporator 28 and chamber 16 when the valve 22 is open and the valves 18 and 20 closed. The connections between the sterilizer 12 and chamber 16 are of an adequate size to enable equalization in a minimum time.

When the pressure in the sterilizer 12 has reached its predetermined minimum level and the cycle is at a stage where it requires the admission of sterilent vapour, valve 22 is closed whilst valve 18 simultaneously is opened.

The vacuum in the chamber 16 will then draw in sterilent from the sterilent source 24 and will either fill or partially fill the chamber 16 and its associated pipework until the decay in the vacuum pressure is balanced by those pressure losses upstream from the chamber. The intake of sterilent occurs over a timed period, sufficient to allow the vacuum to draw the predetermined amount of sterilent into the chamber 16.

After this timed period, valves 18 and 22 are simultaneously reversed, such that, valve 18 is closed and valve 22 opened. The sterilent in the chamber is now acted upon by the vacuum upstream of valve 22 and is therefore drawn into the evaporator (vapouriser) 28 which has a volume much greater than the volume of the chamber 16.

The design and size of the evaporator 28 is such that the liquid sterilentwhich enters therein, remains inside to be heated, and only vapourised sterilent leaves to pass into the sterilizer 12. When all the sterilent has been vapourised, the pressure within the chamber 16 will once again follow that within the sterilizer 12. The contents within the sterilizer 12 are exposed to the sterilent vapour over a timed period. This is normally followed by the direct introduction of steam (not shown in the drawings) into the sterilizer 12 to create a condition of maximum sterilizing effect. After a further timed period this mixture of steam and sterilentvapour is evacuated from the sterilizer 12. Once evacuated the chamber 16 is again ready to accept further liquid sterilent.

Such a cycle may be repeatedly operated, and priorto temporary shut down of the sterilizer, the valve 20 is opened in orderto allow steam from the source 26to clean (purge) the chamber 16 and evaporator 28 from any residue sterilent.

Alternatively or in addition, the valve 20 and steam source 26 are used as the component to introduce steam into the sterilizer 12 in orderto create the aforementioned condition of maximum sterilizing effect.

The metering apparatus 14 is also provided with a non-return valve 30 between the chamber 16 and valve 18 as a safety check to the passage of steam to the source of sterilent 24 in the event of failure of the valve 18.

In Figure 2, the system 50 also incorporates a metering apparatus 14 and a sterilizer 12.

The metering apparatus 14 is, however, slightly modified to that used in Figure 1, in that valves 18 and 22 are replaced by a single two-way valve 52. In operation, with valve 20 closed and valve 52 opened between the chamber 16 and evaporator 28, the steady state conditions of the sterilizer 12 can be duplicated within the chamber 16. Having attained the required vacuum in the chamber 16, the valve 52 can be operated to close the line to the evaporator 28 but open the line to the sterilent source 24.

Similarly, when the chamber 16 has received all the sterilent it can draw, the valve 52 is reversed to allow the drawn sterilent to flow into the evaporator 28 and sterilizer 12. Also similariy, steam can be made to pass through the chamber 16 and evaporator 28 when the valve 20 is opened.

The chamber 16 of Figures 1 and 2 can be of a fixed capacity or designed so that its volume may be varied. The valves 18,20,22 and 52 can be operated pneumatically or hydraulically but for quickness of response it is preferred to operate electrically.

The systems 10 and 50 operate at low temperatures for example around 75"C, and are useful for destroying both vegetative and sporing organisms in applications where heat sensitive items are to be sterilized. The creating of a vacuum in the chamber 16 and the subsequent use of this vacuum to draw in substantially fixed metered amount of sterilent, has been found to provide a series of fixed amounts of sterilent accurate in volume and weight to within 1 to 2% of each other.

Claims (15)

1. A method of metering sterilent into a sterilizer comprising creating a vacuum or sub-atmospheric pressure within a chamber, opening a source of sterilent to the chamber such that sterilent is drawn therein by the vacuum,.closing the source of sterilentto the chamber when a predetermined pressure in the chamber is reached, and releasing the consequently metered amount ofsterilentfrom the chamber to a sterilizer.

2. A method as claimed in claim 1 wherein the sterilent is released from the chamberfirstly into an evaporator prior to introduction into the sterilizer.

3. A method as claimed in either claim 1 or 2 wherein steam is introduced into the sterilizer after the metered amount of sterilent is released into the sterilizer.

4. A method as claimed in claim 3 in which steam is introduced into the sterilizer via the chamber and/or evaporator.

5. A method as claimed in any preceding claim wherein steam is passed through the chamber and/or evaporator after sterilent is introduced into the sterilizer, to clean or purge any residue sterilent.

6. A method as claimed in any preceding claim wherein the sterilent is Formalin.

7. A method as claimed in any preceding claim wherein the sterilent is introduced into the sterilizer as a Formaldehyde vapour.

8. A sterilent metering apparatus for a sterilizer comprising a chamber in which a vacuum subatmospheric pressure may be periodically created, first valve means to open and close the chamber from a source of sterilent, and second valve means between the chamber and the sterilizer.

9. An apparatus as claimed in claim 8 including an evaporator between the second valve means and the sterilizer.

10. An apparatus as claimed in either claim 8 or 9 wherein third valve means are provided to open and close the chamber to a source of steam.

11. An apparatus as claimed in any one of claims 8 to 10 wherein the first and second valve means comprise two separate valves.

12. An apparatus as claimed in any one of claims 8 to 10 wherein the first and second valve means comprise a single two-way valve.

13. A sterilizer including a sterilent metering apparatus as claimed in any one of claims 8 to 12.

14. A method of metering sterilent substantially as herein described with reference to Figure 1 and 2 of the accompanying drawings.

15. A sterilent metering apparatus substantially as herein described with reference to figure 1 or 2 of the accompanying drawings.