Access device for containers of fluidizable substances comprising a body (1) provided with a hollow spike (4) designed to be inserted into a container (F) of a substance to fluidize and having an axial fluid passage (5) and an axial passage (6) for venting of the container (F), an expandable chamber (14) connected to the venting passage (6) of the spike (4) through a lateral passage (7) of the body (1), a first check valve (24) enabling one-way communication from the lateral passage (7) to the expandable chamber (14), a second check valve (23) enabling one-way communication from a vent opening (25) to the venting passage (6) of the spike (4). A double impermeable filtering membrane (22a, 22b) is interposed between the first check valve (24) and the second check valve (23).
