GB2199496A - Autoclave steam control - Google Patents

Abstract

A sterilizing apparatus comprises an autoclave (10) having a steam outlet (20), a valve (21) in the steam outlet, an electrical timer (23) controlling the valve to produce a succession of on-off actions of the valve during a steaming period, and a timing and temperature control system (13) controlling the overall steaming cycle and coacting with the timer (23) to control the duration of the steaming period. The opening and closing of the exhaust valve causes turbulence of the steam in the autoclave so that steam more quickly reaches the interior surfaces of the articles. <IMAGE>

Description

TITLE: AUTOCLAVE STEAM CONTROL This invention relates to a method of and apparatus for controlling the entrance and exit of steam for a steam sterilising autoclave.

Such an autoclave is used inter alia for the treatment of contaminated articles such as glass or plastic bottles, Petri dishes and sample tubes and to steam these to a high temperature before reuse or disposal of these articles into a waste bin. One known method is to close the autoclave, pump out some air and feed in steam from an external source. The steam is then pumped out together with more air via a valve.

In another arrangement steam is supplied externally to the autoclave and is permitted to exhaust continuously for a sufficient period (known as the free steaming period) to remove the air. Thereafter the exhaust outlet is closed and steam inlet continued until the desired high temperature is reached whereupon the temperature and pressure are maintained for a given period.

Both these methods require a considerable time and this operation is normally carried out several times a day. Because of the random type and disposition of the articles when sterilization is carried out prior to waste disposal a somewhat lengthy time of exposure to steam is required to ensure that steam reaches all the surfaces within and between the articles.

The main object of the present invention is to ensure sterilization of all such articles in a shorter time than is normally required in prior art processes.

According to the method of the present invention the exhaust of steam from an autoclave is closed and opened a plurality of times during a cycle of steaming. This causes a turbulance of steam in the autoclave on each opening of the exhaust so that steam more quickly reaches all interior surfaces of the articles and the required maximum temperature is reached in a shorter period of time than is possible by the known methods.

For carrying out the method the invention provides an apparatus comprising an autoclave having a steam inlet, a steam outlet, a valve in the steam outlet, an electrical timer controlling the valve to produce a succession of on-off actions of the valve during a steaming cycle and a timing and temperature control system coacting with the timer to control overall steaming period.

The invention will be further described with reference to the accompanying drawings wherein: Figure 1 is a schematic diagram of a steam control system made in accordance with the invention; and Figure 2 is a graphical diagram showing the time/temperature characteristics.

In Figure 1 an autoclave 10 is shown with an internal electrical heater in a water reservoir 11 which however may be replaced by steam from an external source. Water level is shown at 12. An electronic timing and temperature control device 13 is connected to a temperature sensing element 16 and/or to a pressure sensing element 17 both within the autoclave 10 and to a heater control means 18 or a steam supply control means.

The autoclave has a steam outlet pipe 20 provided with a steam control valve 21 the opening and closing of which is controlled by electrical signals from an electrical on/off cycle timer 23 which is provided with on and off time adjusting means 25,26. This timer is subject to overall control by electrical signals from the output 28 of the control system 13. The timer 23 may be arranged to operate continuously but is effective to operate the valve 20 only when enabled by signals from the system 13. Preferably the timer is set to provide a closed period of about 120 seconds and an open period of about 20 seconds. However, the timing is dependant upon the type of load.

The opening and closing of the valve takes place during the "free steaming" duration. When the valve closes pressure in the autoclave rises above atmospheric pressure. When the valve opens steam pressure is released rapidly and an exhaust turbulence occurs which assists extraction of air trapped within the articles.

The efficiency of the high-temperature steam sterilization period is improved and the duration required at this high temperature is reduced if the entire load attains a temperature sufficiently close to the steam temperature before the steam exhaust control valve is closed.

The load may not necessarily attain 100 degrees C, but instead a temperature close to this, i.e. 95 degrees or more. The steam 'penetration' mostly occurs during the 'freesteaming' phase. Once the exhaust is closed the further penetration of steam is slowed down considerably so the need is to get the steam into the load first and then raise the temperature by closing the valve.

Figure 2 illustrates the effect of operation of the invention according to one example.

The upper graph shows the water and load characteristics (K and L) from which it is seen that in this example the point (N) at which the load reaches a temperature sufficiently close to the temperature of the steam in the vessel is achieved at time tl (e.g. 56 mins). Maximum and sterilization effectiveness of the steam is achieved during the period after point N is reached.

The lower graph shows exhaust valve opening periods (0) and closed periods (C). Curve K indicates the vessel steam temperature characteristic and curve L1 the load temperature charasteristic.

It will be seen that with the present invention the required temperature (N ) of the load is reached more quickly e.g. in 36 mins thus saving operating time (t1 t2 ).

Claims (8)

1. A sterilization method in which the exhaust of steam from an autoclave is closed and opened a plurality of times during a cycle of steaming.

2. A sterlilization apparatus comprising an autoclave (10) having a steam outlet (20), a valve (21) in the steam outlet, an electrical timer (23) controlling the valve (21) to produce a succession of on-off actions of the valve during a steaming period, and a timing and temperature control system (13) controlling the overall steaming cycle and coacting with the timer (23) to control the duration of the steaming period.

3. A sterilization apparatus as claimed in Claim 2, wherein said autoclave includes an internal electrical heater (11) electrically connected to an output of said control system (13).

A k sterilization apparatus as claimed in Claim 2, wherein said autoclave is provided with a steam inlet through which steam can enter at each opening of the exhaust valve.

5. A sterilization apparatus as claimed in Claim 2, 3 or 4 wherein said autoclave is provided with a temperature sensing element (16), and/or a pressure sensing element (17), said temperature element and/or said pressure sensing element being electrically connected to inputs to the timing and temperature control system (13).

6. A sterilization apparatus as claimed in any one of Claims 2-5, wherein said electrical timer (23) is provided with adjusting means (25,26) by which the on and off periods of the valve (21) operating signals.

7. A sterilization apparatus as claimed in Claim 6, wherein said timer (23) is arranged to operate continuously but is effective to operate the valve (21) only when enabled by signals at the output of the control system (13).

8. A sterilization apparatus substantially as described with reference to Figure 1 of the accompanying drawings.