Autoclave vacuum leak test: what it is and how to do it
— Equipo JP Selecta
The vacuum test of an autoclave, or leak test, checks the tightness of the system by subjecting the chamber to a pressure below atmospheric pressure and measuring how much it rises over a defined interval.
It is carried out with the chamber empty and under the thermal conditions specified by the manufacturer. Its frequency depends on the unit and on the laboratory's procedure. It is also relevant after interventions that may affect tightness.
The test makes it possible to detect an ingress of air that is incompatible with the unit's acceptance criterion. On its own, it does not demonstrate the sterility of a load, nor does it replace the steam penetration test.
Why is vacuum critical in steam sterilisation?
Saturated steam transfers heat by condensing on the material. For contact to be effective, the air must be adequately removed. A leak can introduce gases during the vacuum phases and hinder steam penetration.
Controlling the cycle time and temperature does not replace checking tightness: the two pieces of evidence answer different questions within process control.
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What exactly does the vacuum test assess?
The test assesses the ability of the system as a whole to maintain the vacuum under defined conditions. It provides information on the tightness of the chamber, the door closure, the valves and the connections subjected to the test. The evacuation phase also makes it possible to notice that the expected vacuum is not being reached, although the test is not equivalent to a full diagnosis of the pump.
An excessive pressure rise calls for investigation. It may be related to a leak, but also to residual moisture, outgassing or inadequate thermal preparation. For this reason, an unfavourable result does not on its own identify the faulty part. Checks and repairs must follow the manual and be carried out by authorised personnel.
How is the vacuum test carried out?
The automatic programme defines the phases and the acceptance criterion. It must be used without transferring the parameters of a sterilisation cycle to the test.
- Prepare the autoclave empty, without a load (avoid mistakes when loading the autoclave), cold and dry when the manual so specifies. Keep only the accessories that the manufacturer authorises for the test.
- Visually inspect the seal and the sealing surface. Then remove any dirt using the permitted procedure.
- Select the vacuum test programme and close the door correctly.
- Start the evacuation and let the system reach the programmed pressure. The number of pulses depends on the model: three pulses should not be assumed for every unit.
- Let the stabilisation and measurement phases complete without opening the door or interrupting the programme. Stabilisation helps to reduce variations that could be mistaken for a leak.
- Check the result and the pressure rise rate against the established limit. A frequent technical reference is approximately 1.3 mbar/min, equivalent to about 1 mmHg/min, but the documented criterion for the unit and the applicable procedure prevails.
| Parameter | Reference value | Reference standard | Context |
|---|---|---|---|
| Maximum pressure rise (reference) | ≤ 1.3 mbar/min | EN 285 / EN 13060 | Large and small sterilisers |
| Approximate equivalent | ≈ 1 mmHg/min | — | — |
- Record the date, the unit identification, the programme, the result and the person responsible for the review. Keep the report accessible and document any incident.
If the result is not acceptable, suspend the affected cycles and report the incident to the person in charge. Do not compensate for a leak by increasing the sterilisation time. After correcting the cause, repeat the planned checks before authorising the return to service.
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When and how often should the vacuum test be carried out?
The frequency depends on the design of the autoclave, how intensively it is used, the loads and the quality system. It must be set out in a written procedure, together with the actions to take in the event of a failure.
In any case, the test should be scheduled with enough time to meet the preparation conditions, especially when it requires a cold unit.
- Routine use: apply the frequency indicated by the manufacturer and by the laboratory's control plan. If that plan requires it, the check will be daily.
- After replacing the seal or working on valves and connections: check tightness before using the affected cycles again.
- After maintenance, repair or relocation: assess the return-to-service checks according to the scope of the intervention.
- In the event of vacuum alarms or abnormal penetration results: investigate and carry out the relevant tests; do not simply repeat the test until you obtain a satisfactory result.
| Context of use | Example frequency (set by the facility's procedure) |
|---|---|
| Pharmaceutical laboratory (GMP) | Daily (start of the working day) |
| Hospital / surgical instruments | Daily (before the first sterilisation) |
| Research laboratory / university | Weekly or according to the procedure |
| After repair or maintenance | Immediate (before resuming cycles) |
| After replacing the door seal | Immediate |
The vacuum test within the GMP control of the unit
In a GMP environment, the test forms part of the documented control of the unit when the applicable procedure requires it. Its result is kept, reviewed and linked to incidents and corrective actions. It does not replace IQ/OQ/PQ qualification or the validation of sterilisation processes.
At J.P. Selecta we offer the Autester ST DRY USB-S and GMP-S fractionated vacuum autoclaves, with vacuum and Bowie-Dick tests, data logging for more than 500 cycles and data transfer via FTP.
An electronic signature or full regulatory compliance must not be attributed to a unit simply because it exports records.
Discover all the laboratory autoclave options in our catalogue.
Frequently asked questions
What is the vacuum test in a laboratory autoclave?
It is a test that measures the pressure rise in an evacuated chamber to check whether air ingress remains within the established limit.
How often should it be carried out?
At the frequency set out in the manual and the control plan, and after interventions that may affect the vacuum system or its tightness.
What does a negative result mean?
It usually indicates that the pressure rise exceeded the limit and the test is not acceptable; terminology varies between units, so check it in the manual. If so, investigate the cause and do not use the affected cycles until the issue has been resolved and verified.
Do all autoclaves need to perform it?
It applies to units with vacuum systems and a planned test procedure. It does not apply to models with manual or atmospheric air purging, which have no vacuum system.
What is the difference between the leak test, Bowie-Dick and Helix?
The leak test checks tightness. Bowie-Dick assesses air removal and steam penetration in a defined challenge. Helix uses a device that presents a penetration challenge associated with a narrow cavity. They are complementary checks and each one requires an appropriate cycle and an appropriate device. The DART test is a commercial device with the same purpose as the Bowie-Dick test.