Tapered labyrinth

Obviously, oil leakage may be caused by leaking mechanical seals. In turboexpander compressors, however, the most common cause is improperly designed labyrinth seals. Tapered labyrinth designs seem more prone to suffer from this defect. 

In the tapered labyrinth (Figure 5-5), a fixed labyrinth seals against a tapered shaft. As the shaft moves axially, the clearance of the seal changes. This allows an excess seal gas flow. The resulting venturi effect actually drags the lubricating oil into the process stream. Also, since the tapered shaft seal makes it difficult to provide an effective oil slinger, the problem is compounded. 

Damage to the labyrinth requires replacement of the expander heat barrier or compressor shaft seal. A replacement design (Figure 5-6) uses a replaceable stainless-steel labyrinth mounted on the shaft. Because the seal is not tapered, axial movement of the shaft has little or no measurable effect on seal gas flowrates. Each labyrinth has an integral oil slinger incorporated into the design. Also, each rotating... 

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