The vacuum decay method (VDM) is a packaging quality control system that verifies the integrity of a hermetically sealed container in a non-invasive and non-destructive manner, using methods that damage neither the packaging nor the product inside it.
This testing method is increasingly common in industry and offers many advantages. That is why it is recommended in USP chapter 1207.1, where it is listed as one of the six main types of non-destructive and deterministic tests:
The vacuum decay method of leak testing uses a vacuum to detect leaks in a sealed package.
The product to be tested is placed in a test chamber where a certain vacuum level is applied (variable depending on the type of product, its shape, and the desired degree of accuracy, between -980 and 20 millibars absolute). Each test chamber is designed to match the shape of the product to be tested as closely as possible to minimize the required internal volume, thereby reducing the time necessary to reach the desired vacuum level. Once the vacuum level has been attained, two readings of the internal pressure value are taken, a few seconds apart. If the difference between the two values is greater than the physiological threshold set during machine configuration (parameters set for the test), the container has a leak and is rejected. Products in which no leak is detected continue through the production line for packing, storage, and shipping.
VDM offers many advantages:
The application of VDM to flexible packaging (such as bags containing liquid for IV or plastic containers produced using blow-fill-seal technology) is slightly trickier then testing rigid packaging. This is because products may contain air, and might expand excessively during testing, distorting the result. Flexible containers may also be too large to be tested quickly using a vacuum.
These challenges can be overcome by using alternative solutions based on the characteristics of each product to be tested. One of the approaches used by Bonfiglioli Engineering is to include one or more sensors providing information on the level of product deformation inside the test chamber, in addition to the VDM test. By pairing the two test methods and creating increasingly customized test chambers, VDM can also be used to test flexible packaging, with no loss of accuracy or decrease in the reliability of the result.
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