Abstract: A sealing device wherein at least one of the sealing assemblies comprises at least two concentrically arranged rigid wedge rings having confronted conical surfaces, the inner and outer rings having respective inner and outer cylindrical surfaces slidingly confronting the plunger and the cylinder recessed portion, respectively, whereby axial compression of the wedge rings of each sealing assembly causes relative axial displacement and thus radial expansion thereof and forced mating of all confronting surfaces of said rings, plunger and cylinder, wherein the low-pressure end of one of the wedge rings of the first sealing assembly operatively abuts against the corresponding step of the cylinder recess while the second sealing assembly is slidably mounted in the recess and the high-pressure end thereof is exposed to the compressed liquid; and wherein an intermediate chamber defined in the recess between the sealing assemblies is filled with a sealing liquid to which the high pressure of the compressed liquid is t