A METHOD OF TESTING THE AIRTIGHTNESS OF A CONTAINER

Abstract: The invention concerns a method of performing an air leakage test in a low pressure chamber. The chamber is evacuated down to a predetermined low pressure level, at which level the evacuation is interrupted and the chamber closed entirely. Following a period of inactivity after attainment of the predetermined low pressure level, during which period the pressure is allowed to rise inside the chamber, the evacuation is again started. This is effected with the aid of an ejector having a higher capacity for pumping out vapour than air, and the evacuation is effected until the predetermined low pressure level is again attained.

Description: A METHOD FOR TESTING THE AIRTIGHTNESS OF A CONTAINER The invention concerns a method of performing a test inside a low pressure chamber, such as an autoclave, in order to verify whether air is present or leaks into the chamber during an ongoing process in said chamber. Tests of this kinds are performed regularly with respect to autoclaves intended for sterilization of goods of the most disparate nature. The process is divided into several part processes, such as a pretreatment during which the chamber is evacuated, a sterilizing period during which sterilization is carried out at a vapour overpressure, and a post-treatment during which the sterilizing goods is dried at a low pressure. During a process of this kind by means of vapour it is most essential that no air remains in any trapped air-pockets in the goods to be sterilized, preventing the vapour from completing the sterilizing in these traps. Should this happen, the consequences could be serious when the equipment, believed to be sterile without being so for the reasons outlined above, is to be used again. Medical instruments and implements and medical and nursing articles are examples of equipment of this category. One method widely employed today for testing the airtightness of low pressure ' chambers, such as autoclaves, is performed in the following manner. After stabilization of the temperature in a chamber which is empty apart from stationary equipment, such as e.g. manometers, manometer tubes and measuring sensors of other kinds, the testing process is initiated and lowers the pressure inside the chamber at least down to a pre- determined level. This level being reached, the evacuation is stopped and all valves are closed. The time and the absolute pressure are registered. After the lapse of a few minutes to allow the condensate inside the chamber to evaporate, the pressure and the time are again registered. A renewed registration of the pressure and the time is made after another couple of minutes. At the end of this test period the magnitude of the pressure increase during the last operational phase is calculated, which pressure increase must not exceed a predetermined value in order for the chamber to be considered allowable. This conventional airtightness test requires a knowledgable as well as a skillful servicing operator to perform the test, in addition to which the test must be carried out over a comparatively long period in order to ensure a trustworthy result, i.e. to make it possible to verify to which extent the pressure increase, after evacuation, could be considered the result of evaporation of the condensate or of air leakage. The present invention provides a method by means of which it becomes possible to perform leakage tests in quicker and at the same time easier manner without foregoing the requirements on accuracy. To this end, the invention is based on the use of an ejector which is adapted to pump vapour rapidly but to pump air at a lower rate. A water jet pump meets this description. The particular features characterizing the method are defined in the appended claims. The invention will be described in closer detail in the following with reference to the accompanying drawings, wherein Fig. 1 is a graph of a conventional leakage method and illustrates the pressure as a function of time, and Fig. 2 is a corresponding graph illustrating the method in accordance with the present invention. For a deeper understanding of the invention the conventional leakage method will initially be described with reference to Fig. 1. Following stabilization of the temperature in the low pressure chamber to be measured the testing process is initiated by lowering the pressure inside the chamber to a level corresponding to a satisfactory "vacuum" pressure. This level could for instance be an absolute pressure of 70 mbar or slightly below. The pressure pi and the time t are registered, once the evacuation has been interrupted and all valves have been closed. Some minutes are allowed to lapse, in the example of the drawing figure 300 s, whereupon the pressure p 2 and the time t 2 are measured. Following a further few minutes, in the example of the drawing figure 600 s or slightly more, the pressure p 3 and the time t 3 are registered, whereafter the valves of the chamber are opened. According to an established standard, the pressure from time t 2 to time t 3 must not exceed 1.3 bar/min, i.e. in accordance with the shown embodiment the pressure p 3 minus pressure p 2 must not exceed about 13 mbar in order for the leakage test to be allowable. In this case the described graph thus shows a non-allowable leakage. In accordance with the invention, the process starts in an identical manner by stabilization of the temperature inside the chamber. Vapour is then blown into the chamber, which is shown by an increase of the pressure to a level slightly above the atmospheric pressure, whereupon the chamber, in the same manner as hitherto, is evacuated to a level of a strong low pressure, ' which could be e.g. 70 mbar or slightly below. Measurement point A in Fig. 2 thus corresponds to point p a in Fig. 1. The autoclave is then allowed to be inactive for some minutes during which period the pressure rises as a result of the evaporation of the condensate in the chamber, e.g. along the continuous line from point A to point B in Fig. 2. At this point, another evacuation phase is started by means of an ejector which pumps out vapour rapidly and, at a slower rate, air. Advantageously, an water jet pump is used. The evacuation is continued until the pressure reaches point C in the graph of Fig. 2, and this point should be at the same level as point A or preferably slightly below. The evacuation is then interrupted and the valves of the autoclave are opened, causing the pressure to rapidly rise to the atmospheric pressure. As appears from Fig. 2, dashed lines define a first time period between point A and point B, denoted leakage period, and a second time period, denoted measuring period. Should, during the evacuation from point B, point C be reached within this measuring period, this is an indication that no or only insignificant air leakage occurs in the autoclave. A dash-and-dot line indicates a second measurement from point A to point B 1( the latter being at a somewhat higher level than point B. During the evacuation from point Bx the same dash-and-dot line indicates that the level of point C is not reached within the prescribed measuring period. As a result, the test may be interrupted, and the fact that the airtightness of the autoclave is unsatisfactory is verified. The air leakage that one intends to detect with the aid of the invention thus does not have to cause a noticeable additional pressure increase during the inactive period which is denoted leakage period in Fig. 2 (cf. pressure differential Bχ-B) . Instead, a considerable increase of the measuring time is found when from the higher pressure Bx one is to reach the level of point C. In accordance with the shown embodiment an increase of the measuring time by about 15s applies. Reversely, for tests where no verification of the existence air leakage is found, it becomes possible to interrupt the test after a short duration. Consequently, information on the prevailing conditions may be obtained a great deal more rapidly than in the case of the conventional method according to Fig. 1. The method according to the invention is applicable to automatic autoclave airtightness testing programmes according to which the programme ends by e.g. the emission of a red signal indicating 'error' and a green signal 'passed' . The method is well suited for automatic operation because of its sensitivity to detection of air.

Claims: CLAIMS 1. A method of performing a test inside a low pressure chamber, such as an autoclave, in order to verify whether air is present or leaks into the chamber during an ongoing processin said chamber, according to which method, the temperature in said chamber is stabilized, whereupon the chamber is evacuated down to a predetermined low pressure level, at which the evacuation is interrupted and the chamber is entirely closed by closure of all existing valves, c h a r a c t e r i z e d in that after a period of inactivity following the attainment of the predetermined low pressure level, during which period the pressure is allowed to rise inside the chamber, the evacuation is re-started with the aid of an ejector of a kind having a higher capacity for pumping out vapour than air, preferably a water jet pump, said re-newed evacuation continuing until said predetermined low pressure level is again attained. 2. The method as claimed in claim 1, c h a r a c t e r i z e d by setting a predetermined mesuring period calculated from the start of the re-newed evacuation, and by interrupting said evacuation, should the predetermined low pressure level not have been attained within the set measuring period. 3. The method as claimed in any one of the preceding claims, c h a r a c t e r i z e d in that vapour is blown into the chamber prior to the first evacuation for the purpose of forcing air out of the chamber.

Inventors: AMBERNTSSON JAN, AMBERNTSSON, JAN
Applicants: AMBERNTSSON JAN, GETINGE SKAERHAMN AB, AMBERNTSSON, JAN
Application year: 1997
Main classification: G01M3
IPC codes: B01J3, G01M3