Type 28AT: The original gas seal, with a design pedigree stretching back over 30 years and evolving gradually, installed and proven in thousands of compressors all around the world and remaining the preferred seal choice for many customers. Type 28 compressor dry-running gas seals have been the industry standard since early 1970 for gas-handling turbomachinery. Utilizing John Crane’s patented spiral groove pattern, these seals are non-contacting in operation. During dynamic operation, the mating ring/seat and primary ring/face maintain a sealing gap of approximately 0.0002″/5 microns, thereby eliminating wear. These seals eliminate seal oil contamination and reduce maintenance costs and downtime. Single, tandem and double seal arrangements are available.