A shaft extending along and rotatable about an axis and a housing surrounding a portion of the shaft are provided with a seal assembly having an inner ring fixed on and rotatable with the shaft and having a pair of axially oppositely directed outer faces and a pair of outer slide rings axially flanking the inner ring and having inner faces axially sealed on the inner-ring outer faces. The outer rings, the housing, and the inner ring form an annular housing compartment surrounding the shaft. A blocking compartment on the housing is separate from the housing compartment. The inner ring is formed with a radially throughgoing passage having an inner end open on the shaft and an outer end open into the housing compartment. The housing is formed with a bore between the housing compartment and blocking compartment.