Describe : Gas Lubricated, Non-Contacting Gas Seals For Turbo Compressors Type 28 compressor dry-running gas seals have been the industry standard since the early 1980’s for gas-handling turbomachinery. Supported by John Crane’s patented design features, 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 in./5 microns, thereby eliminating wear.