Pressure differential techniques can be classified into two groups - external pressure methods and vacuum methods. Smithers Pira has facilities to evaluate the integrity of packages using both techniques.
The vacuum method is suitable for packages having a well-defined headspace. It relies on gas or liquid flow because the pressure inside the package is higher than the pressure in the vacuum chamber. It is suitable for detecting gross leaks (≥ 100µm) and for testing the seal strength of packages under differential pressure conditions such as those which can occur during air transportation.
Smithers Pira employs a Lippke 4500 Package Testing System to test smaller packages using vacuum methods including ASTM D3078 "Standard Test Method for Determination of Leaks in Flexible Packaging by Bubble Emission".
Vacuum methods are not suitable for detecting smaller leaks, especially when the package contains a wet product which may "plug" the leakage route.
Smithers Pira also tests packages in accordance with ASTM D4991.This test method covers the testing of empty containers for resistance to leakage under differential pressure conditions such as those which can occur during air transport. A larger bespoke made vacuum chamber is used for this purpose.
External pressure method
In the external pressure method, the external pressure causes the test gas or liquid to flow from the outside to the inside of the package. A greater differential pressure can be used compared to the vacuum method and the method does not require a headspace in the package.