A rotation mechanism includes: a housing; a shaft inserted through a hole provided at the housing; bearings installed at the housing and rotatably supporting the shaft; a rotary member provided at one end portion of the shaft, adapted to be rotated together with the shaft, and having a portion that projects to a radially outer side of the hole and faces the housing with a gap having a predetermined size; and a gas passage adapted to connect the gap to outside of the housing and allow gas contained in a portion of the gap to pass to the outside of the housing.

The present invention relates to a brushless motor (1), in particular as a drive for a pump for conveying a fluid, having at least one housing (2), at least one stator (3) and at least one rotor (4), wherein a fluid can flow through the housing (2) at least in a gap (5) between the stator (3) and rotor (4) in the housing (2), wherein the stator (3) is formed in a fluid-tight stator chamber (6), and wherein the rotor (4) is formed in a fluid-tight manner.

A compact motor (1), which ensures high requirements for sealing against ambient media, is realized in that the stator chamber (6) is limited in the direction of the rotor (4) by at least one inner sleeve (8), and in that at least one rotor bearing element (9) for mounting the rotor (4) is supported on an inner circumference (10) of the inner sleeve (8).

A rotary feed-through, designed to transfer a fluid between two entities in rotary motion with respect to one another. The rotary feed-through includes an inner cylindrical ring and an outer cylindrical ring, which are free to turn with respect to one another and provided with channels for passage of the fluid. The channels are connected via at least one annular space axially delimited by seal rings housed in a cylindrical seat. The cylindrical seat faces radially outwards or inwards and is axially delimited, on one side, by an axial abutment of the inner and outer cylindrical rings and, on the other side, by an axial abutment of a lid, a closing ring, or an intermediate ring. The seal rings are interference fitted to the inner or outer cylindrical ring and provided with an elastic portion for contact with the surface of the inner or outer cylindrical ring.

A main bearing unit of a wind turbine drivetrain is provided, including a number of bearings arranged about a low-speed shaft of the drivetrain; a housing arranged to enclose the bearings; a preload ring arranged between an inner surface of the housing and the outer race of a bearing, which preload ring is adapted to facilitate its axial displacement during a bearing preload reinstatement procedure; and a fastener for fixing the position of the preload ring to the housing following a bearing preload reinstatement procedure. Also provided is a bearing preloading arrangement for use in reinstating preload in a bearing of such a main bearing unit; and a method of reinstating a preload force in a bearing of such a main bearing unit.