Chamber at variable internal pressure, comprising a sealed-connection assembly able to slide inside a plane of translation, the said connection assembly itself comprising: - a first rigid component provided with an orifice (O 1) and with a first planar surface (S 1) surrounding the said orifice; and - a second rigid component provided with a second planar surface (S 2) surrounding a central part of the said second component; the first and second components being arranged in such a way that the central part of the second component faces the orifice of the first component with the first and second surfaces parallel and facing one another, out of the first and second surfaces, one of them comprising a groove surrounding the orifice or the central part, respectively, along a closed path, and the said connection assembly further comprising: - a flat seal, with a planar active surface (S 3) in the shape of a circular ring, and arranged in the groove in such a way that the active surface of the said flat seal is in continuous contact along the closed path with the planar surface (S 2) of the other of the first and second components than the one which comprises the groove, and referred to as the counter-surface; - at least one first o-ring seal, arranged between the flat seal and a bottom of the groove, a depth of the groove being somewhere between a thickness of the first o-ring seal and a sum of the said thickness of the first o-ring seal with a thickness of the flat seal; - a system (30, 31) for bringing about a movement of the first and second components one relative to the other along two axes (X, Y) which are parallel to the plane of translation, which system is able to cause the active surface (S 3) of the flat seal to slide against the counter-surface (S 2); and - a system for clamping the first and second components, the clamping system being arranged to compress the flat seal against the counter-surface (S 2), producing a compression force on the said flat seal through the first o-ring seal, perpendicular to the plane of translation, in which chamber the said first rigid component forms at least part of a wall of the said chamber and the second rigid component is connected to a support extending inside the said chamber so that the said support is able to move with respect to the chamber in directions of translation which are parallel to the said plane of translation when the system (30, 31) for bringing about movement is actuated. - a first rigid component provided with an orifice (O 1) and with a first planar surface (S 1) surrounding the said orifice; and - a second rigid component provided with a second planar surface (S 2) surrounding a central part of the said second component; - a flat seal, with a planar active surface (S 3) in the shape of a circular ring, and arranged in the groove in such a way that the active surface of the said flat seal is in continuous contact along the closed path with the planar surface (S 2) of the other of the first and second components than the one which comprises the groove, and referred to as the counter-surface; - at least one first o-ring seal, arranged between the flat seal and a bottom of the groove, a depth of the groove being somewhere between a thickness of the first o-ring seal and a sum of the said thickness of the first o-ring seal with a thickness of the flat seal; - a system (30, 31) for bringing about a movement of the first and second components one relative to the other along two axes (X, Y) which are parallel to the plane of translation, which system is able to cause the active surface (S 3) of the flat seal to slide against the counter-surface (S 2); and - a system for clamping the first and second components, the clamping system being arranged to compress the flat seal against the counter-surface (S 2), producing a compression force on the said flat seal through the first o-ring seal, perpendicular to the plane of translation,