Leak tester is often referred to as vacuum/negative pressure method, or bubble emission method,which is used as gross leak checking for flexible packages(with headspace gas) by eye observation.
Principle:
The specimen is submerged in the water within the vacuum chamber, and then the vacuum chamber is evacuated to form a pressure difference between the inside and outside of specimen. The seal performance can be obtained by observing whether there are steady progression of bubbles from the specimen and how the specimen expands and restores to its original shape after vacuum release.