Summary : Package integrity is often an important characteristic of package performance. Breaches of package integrity may permit substances to enter or contents to escape packages. A Leak means an opening in a flexible package that, contrary to intention, either lets contents escape or permits substances to enter.
Applicable to : Any non-porous package such as Pouches, Blister Packs, Cans, Bottles, etc. This test can also help understand the performance of a package when transported through non-pressurized air cargo or when it is used at high altitudes (low atmospheric pressures).
You must have witnessed the puffed up pouches of dairy creamer (milk powder) or single-serve milk blister packs, served with tea in aircrafts. If the pouches were not strong enough, they would have burst open at these low pressure conditions.
Limitation : This test is can only detect leaks due to reasonable large pinholes or gaps which can allow the fluid or gas to pass out and / or water to enter the package. This test is not suitable for detecting micro leakages or for testing packages containing high viscosity fluids. This test also cannot be used to test vacuum sealed packs.
Test Method :
There are 2 variations to this test.
Dry Test, in which the package is filled with the actual liquid product or more preferably colored water (because water viscosity is usually lower than the actual product).
A white tissue paper or similar, is kept in a Vacuum Dessicator Tank and the package is kept on it. Bottles have to be kept inverted. The tank is then closed and gradually increasing vacuum is applied to the tank upto a predetermined level. The vacuum is then held at that level for a predetermined time period and then released.
If there is any leakage in the pouch, the product (or colored water) would have come out and stained the tissue paper under it. Incase of bottle, the bottle in kept vertical and tapped slightly from the cap. The cap is then removed to see if any product is visible on the lip of the bottle or the threads of the cap.
Wet Test, in which the package either contains a product that is essentially solid or powder and has a considerable amount of air in the headspace. Alternatively you can also fill air in the package. Bottles can be tested empty. The Vacuum Dessicator Tank is filled with water (preferably colored water) and the package is dipped in the water. Suitable method to restrain the package and keep it dipped in water throughout the test. The tank is then closed and gradually increasing vacuum is applied to the tank upto a predetermined level. The vacuum is then held at that level for a predetermined time period during which leaks can be identified as visible streams of air bubbles. Random air bubbles are to be ignored. After the preset time period, the vacuum is released.
If you had seen constant stream of air bubbles, it is a confirmed leakage.
But sometime the bubbles can be random and less distinct in semi-rigid or rigid packs.
In such cases, the packages are opened after the completion of the test and the product is tested for wet or stained spots. Water enters the packs from the leak spots when the vacuum is released.
Stream of Air Bubbles = Leak.
Water inside package = Leak.
Test Standard : ASTM D 3708
Note : There are special purpose machines which use Helium or other Tracer gases to detect even micro leakages which cannot be detected by the Vaccum Leak Test.