Seal for an eccentric-rotor machine

In an eccentric-rotor machine including a housing having a longitudinal axis and defining a plurality of work chambers;

• radial housing walls bounding the work chambers;
• a multi-lobe rotor arranged in the housing for orbital motion therein to sequentially and cyclically decrease and increase the volume of each chamber in the execution of inward and outward strokes, respectively;
• the rotor having opposite radial rotor walls each defining a clearance with an adjacent respective radial housing wall;
• and sealing means arranged in the clearance for sealing the work chambers;
• the improvement wherein said sealing means comprises a sealing ring of circular course;
• said sealing ring being concentric to said axis and having a diameter such that in each chamber a length portion of said sealing ring is situated externally of the outline of the rotor when the volume of the respective chamber is at a maximum, whereby said length portion is out of contact with the respective radial rotor wall during a terminal phase of the outward strokes and a beginning phase of the inward strokes of said rotor and said length portion is in contact with said respective radial rotor wall during a beginning phase of the outward strokes and a terminal phase of the inward strokes.