Abstract: A method of testing the integrity of a package seal (14) provided between a container portion (11) and a lid portion (12), includes the steps of: initially reducing the pressure acting on the outer surface of the container portion to cause the lid portion to bow inwardly to a position of substantially maximum concavity while maintaining the ullage volume within the package substantially constant; further reducing the pressure acting on the outer surface of the container portion to distend the container portion for increasing the volume of the ullage space; and sensing for a change in position of the distended container wall.

Abstract: A leak detector is adapted to test the fluid-tight sealed integrity of a hermetically-sealed package having a movable wall portion. An enclosure surrounds a package-to-be-tested, and the space within the enclosure is evacuated by a vacuum pump. As the pressure acting on the outer surface of the package begins to fall,the gas within the package will be expand, pushing the movable wall portion outwardly. Such displacement of the movable wall portion is sensed and compared with a predetermined value. If desired, the reduced pressure within the enclosure may be held constant for as time interval, and the sensor used to determine whether the distended wall portion has relaxed.