Abstract: A leak-detection installation for testing the gastightness of flexible or rigid sealed packages containing a certain concentration of tracer gas, said installation including a belt conveyor, a bell-shaped cover situated above said conveyor and including drive means enabling said cover to be raised and to be lowered until it bears against the belt of said conveyor, said cover being connected to a tracer gas leak detector, the resulting assembly being controlled by control electronic circuitry, wherein said belt is made of a material that is both non-porous and non-perforated, and wherein the cover carries sealing means at its bottom periphery for co-operating with the belt of said conveyor to guarantee the gastightness of said cover when it is in the low position, wherein the cover is connected to a vacuum pump, and wherein a backing plate provided with a system of sealing rings is disposed under said belt and in alignment with said cover, said backing plate having a recess and being connected to said cover vi