The Kaeser Sliding Ring Seal (also known as a mechanical face seal or axial seal) is a high-precision sealing system used in the air-ends of Kaeser rotary screw compressors to prevent oil leaks and maintain internal pressure. Unlike a standard radial lip seal that grips the shaft, a sliding ring seal uses two perfectly flat, lapped surfaces—one rotating with the shaft and one stationary in the housing. These surfaces are pressed together by spring tension and lubricated by a thin film of Sigma Fluid, creating a hermetic barrier. This design is typically found on larger direct-drive models or high-pressure units where a standard lip seal might not withstand the mechanical stresses.