The Helium or  Vacuum Hood Test is an overall leak test. The evacuated test objects is covered with a (plastic) hood. The space between the test object and the hood is filled with Helium from the search gas reservoir so, the total outer surface of the test object is exposed to the Helium search gas, there are two ways:one is Vacuum method by hood(The testing system is to be considered leak tight if after a period of 10 minutes the system-specific pressure difference amounts to △Psystem < 3 mbar.), the other is Overpressure gas method in hood. Most  widly used in full vessels test