Abstract: A seal for the gap between two relatively rotatable machine parts, in which at least one of the two confronting surfaces is provided with at least one helical groove which has a pumping action toward the sealed space, and in which a preliminary seal is situated ahead of the helical groove on the side facing away from the sealed space. The preliminary seal includes a ring magnet which reaches close to the opposite surface except for a narrow gap. This gap is filled with a ferrofluid, and the radial width of the gap is substantially the same as the distance separating the helical ridges between the helical grooves from the surfaces opposite them.

Abstract: A seal for a magnetizable shaft includes a sealing lip of polymeric material and a preliminary seal on the side facing away from the sealed space. The preliminary seal consists of a ring magnet which surrounds the shaft leaving a gap. A ferrofluid is disposed in this gap.