In the vacuum method, a package is placed inside an enclosed chamber where a vacuum is drawn to create a pressure differential across the package wall. Gas or liquid will flow out of the package if there is a leak or a weak seal, because the pressure inside the package (at about 1 atmosphere) is higher than the pressure in the vacuum chamber. The increase of pressure inside the chamber, the movement of a package's upper wall, or the loss of force applied on the upper wall of a package is monitored using a pressure sensor, a LVDT (Linear Variable Differential Transformer) displacement sensor, or a load sensor, respectively. The vacuum method is suitable for packages having a well-defined headspace. It is suitable for detecting gross leaks (≥ 100 μm) and for testing the seal strength of packages under differential pressure conditions such as those which can occur during air transportation.

• Package
• A chamber equipped with a vacuum decay sensor, a LVDT displacement sensor, or a load sensor
• Vacuum pump

1. Put the package in to the enclosed chamber.
2. Vacuum the chamber.
3. Monitor the decay of vacuum inside a chamber, the movement of a package's upper wall, or the loss of force applied on the upper wall of a package.
4. Record.

Positive

If the monitors detect any changes, the package leaks.

False Positive

If the monitors detect any changes when the package is good sealed, the change might be caused by the unsealed chamber.

Negative

If the monitors do not detect any changes, the package is good sealed.

False Negative

If the monitors do not detect any changes, the leaking channel may be plugged.