TABLE OF CONTENTS Centrifugal compressors in process gas service require shaft sealing to prevent the process gas from traveling down the shaft and escaping the compressor case into the atmosphere. Multistage, beam-style compressors (with impellers located between two bearings) require two seals, one at each end of the shaft (fig. 1-1). Single-stage, -overhung style compressors (with a single impeller located outboard of the bearings) require a single shaft seal, directly behind the impeller.
Early shaft seals were simple labyrinth seals, which oftentimes required complicated eductor/ejector systems to deal with substantial gas leakage through the seals. The next generation of compressor shaft seals was oil film floating ring seals (fig. 1-2). There are two sealing surfaces in a typical floating ring oil seal, the inside diameter of the seal rings and the mating surfaces between the seal rings and the seal housings. Oil is injected into the seal at a pressure slightly higher than the process gas (sealing) pressure. This high-pressure oil forms a seal against the process, and also serves to cool the seal components. Thousands of floating ring oil seals remain in operation today.
Both labyrinth and oil film floating ring seals are radial seals, sealing the radial space created between a rotating shaft and a stationary seal. This limited the level of sealing that could be obtained, because the parts had to operate at a clearance large enough to avoid...
