The pneumatic press comprises a tank (1) having a cylindrical body closed at each of opposite ends by a flange. One of the flanges is equipped with an axial hole for filling the tank in material to be pressed, and other flange is equipped with an axial hole (6) for pressurizing and depressurizing the material. The tank comprises a separation membrane (2) of which the area for connecting to the tank is extended at a level of one flange to a midplane of the tank passing by axial holes and at the opposite flange on the other side of the midplane. The pneumatic press comprises a tank (1) having a cylindrical body closed at each of opposite ends by a flange. One of the flanges is equipped with an axial hole for filling the tank in material to be pressed, and other flange is equipped with an axial hole (6) for pressurizing and depressurizing the material. The tank comprises a separation membrane (2) of which the area for connecting to the tank is extended at a level of one flange to a midplane of the tank passing by axial holes and at the opposite flange on the other side of the midplane so that the membrane separates the interior volume of the tank into two chambers including a treatment chamber in which the axial hole opens for filling the material and a control chamber in which the axial hole opens for pressurizing and depressurizing the material. The part of the flange equipped with axial hole for filling the material, has a protrusion (3) allowing the depressurized state of the control chamber. The protrusion is formed, by a component attached to the flange or by a deformation of the flange, towards inside or outside of the tank from a blank in which notches are formed to define convex folding areas or a longitudinal profile extending substantially in an arc. The deformation of the flange equipped with the axial hole for filling a material. The protrusion has an elongated form and curved into an arc of circle that follows the area for connecting the membrane with the
