OPERATING PRINCIPLE

A vacuum (depression) or a pressure is created inside each can  and the tester verifies the stability of this value after a certain lapse of time: the stability of the vacuum or the pressure is the proof of the tightness of the can and  therefore allows to separate the faulty cans from the good ones.

The greatest parts of the cans can be tested with vacuum that offers, following our experience, the best results in terms of accuracy (leak detection) :  the vacuum permits a faster air stabilization inside the cans, to say "no turbulences"  that is the most important condition to make a good test and then the first parameter to consider  before to proceed with  the measurement of the value. 

Especially for food cans we have a second favorable point for the vacuum: we test the cans on the same condition of their  following use during the filling, so evidencing  the eventually   leaks  due to the stress.

Summarizing we can tell that all cans that offer a sufficient  resistance to the "implosion" can be tested profitably with vacuum, with the exception of the aerosol cans  for which we have other considerations due to the  particular use  of these cans that cannot be compared with the other containers.

In fact the aerosol must be tested with high  pressure: these cans are pressurized up to 12 or 15 bars that permits to detect the  "MICROLEAKS"   (to say a leak range of 1÷2 cc per minute)  :  to avoid the risk of  bursting,  the containers are closed into steel bells that cover completely each  body before the start of the pressuring cycle.

The second family of containers that must be tested with low pressure are the rectangular or square cans  (like those  for olive oil) or in general the shaped cans that don't offer enough axial resistance to the wall deformations: for these cans we adopt particular systems to contain the expansion during the pressurization.