A sealing device adapted to seal and adjust the pressure or flow rate in a tube , for the manufacture by extrusion of this tube, comprising: - an inflatable tubular sleeve having an axis of extension (A) and delimiting at least partially an internal chamber , the inflatable tubular sleeve being flexible and radially deformable between a rest configuration in which the inflatable tubular sleeve has a first maximum external diameter (D1) and an inflated configuration in which the inflatable tubular sleeve has a second maximum external diameter (D2) greater than the first maximum external diameter (D1), - a fluid inlet fluidly connected to the internal chamber and to be connected to an inflation fluid source, the fluid inlet being configured to supply, in use, the internal chamber with inflation fluid so as to radially deform the inflatable tubular sleeve into its inflated configuration, - an internal reinforcement casing disposed around the inflatable tubular sleeve , the internal reinforcement casing comprising at least: - a first internal reinforcing layer which is tubular and consists of reinforcing threads wound helically around the outer surface of the inflatable tubular sleeve and around the axis of extension (A) of the inflatable tubular sleeve in a first winding direction, and - a second internal reinforcing layer which is tubular and consists of reinforcing threads wound helically around the first internal reinforcing layer and around the axis of extension (A) of the inflatable tubular sleeve in a second winding direction opposite to the first winding direction ; characterised in that the sealing device comprises an external reinforcement casing disposed around the internal reinforcement casing , the external reinforcement casing comprising at least one external reinforcing layer which is tubular and consists of reinforcing threads , and in that the internal reinforcement casing is formed of reinforcing threads made of UHMWPE and reinforcing threads made of liquid crystal polymer, and in that the external reinforcing layer consists of reinforcing threads which extend substantially parallel to the axis of extension (A) of the inflatable tubular sleeve . - an inflatable tubular sleeve having an axis of extension (A) and delimiting at least partially an internal chamber , the inflatable tubular sleeve being flexible and radially deformable between a rest configuration in which the inflatable tubular sleeve has a first maximum external diameter (D1) and an inflated configuration in which the inflatable tubular sleeve has a second maximum external diameter (D2) greater than the first maximum external diameter (D1), - a fluid inlet fluidly connected to the internal chamber and to be connected to an inflation fluid source, the fluid inlet being configured to supply, in use, the internal chamber with inflation fluid so as to radially deform the inflatable tubular sleeve into its inflated configuration, - an internal reinforcement casing disposed around the inflatable tubular sleeve , the internal reinforcement casing comprising at least: - a first internal reinforcing layer which is tubular and consists of reinforcing threads wound helically around the outer surface of the inflatable tubular sleeve and around the axis of extension (A) of the inflatable tubular sleeve in a first winding direction, and - a second internal reinforcing layer which is tubular and consists of reinforcing threads wound helically around the first internal reinforcing layer and around the axis of extension (A) of the inflatable tubular sleeve in a second winding direction opposite to the first winding direction ; <EOS>