Abstract: The invention relates to a rotary seal, a vessel and also to use of the vessel. According to the invention, the rotary seal contains a sealing element and a retaining means, the sealing element being configured as a planar structure with an opening which can be changed in its opening cross-section and the retaining means having a first retaining part and a second retaining part (5) which can be rotated relative to each other, and first retaining part and second retaining part respectively being connected securely to the sealing element at least at one attachment point , the attachment points being chosen such that the sealing element can be deformed by rotation of the first and second retaining part such that the opening of the sealing element is reduced in its opening cross-section.