A packer box for use in petroleum drilling is described, in which a rotatable packer element arranged centrically in a packer retainer that is orientable and lockable in a sealing position in a housing in the packer box is arranged to seal against a passing drill string, the packer element comprising a mounting device provided with packer slide rings at the ends of the mounting device and being in sealing abutment against slide rings arranged internally in the packer retainer, and an internal, flexible packer sleeve which is arranged to abut sealingly against the drill string with an external pressure from a fluid in a volume-compensated annular space in the packer retainer, wherein the mounting device includes several channels perforating the mounting device, and clamping devices for fixing the packer sleeve to the end portions of the mounting device. A method of installing or withdrawing a packer element in, respectively from, a packer box is described as well.
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