7.2.2 Foam or film methods
The principle of this method (Fig 4.30) relies on the development of a vacuum in a leaking tube. If the tube is then sealed at each end, the vacuum draws in a foam blanket or a film of polythene or paper, and thus identifies the location of the leak.
Generally two operators, each with a foam generator, are required. Pin-hole leaks with a leakage rate of 400 ml/h can be located, and 5000 tubes/hour can be tested.
The success of this method relies on being able to establish a vacuum of 330 mbar.