Patent attributes
An element is to be mounted on a shaft of a non-positive displacement machine and forms a gap for limited passage of a flowing medium. A bush-like part for mounting on a shaft of the machine has an outer periphery provided with a recess for accommodating a ring. During operation of the machine, the ring, which is partially surrounded on its faces by circular ring-shaped walls of the recess, forms an axial gap with the circular, ring-shaped walls of the recess and a radial gap with the bottom of the recess. The ring is held by frictional contact with a rigid wall which surrounds it. To reduce wear on rings made of soft, flowable material, a second recess is formed in the rigid wall and surrounds the faces of the ring that project from the walls of the bush-like part. One of the lateral bounds of the second recess is formed by a tubular part detachably joined to the rigid wall.