ABSTRACT

This chapter deals with the shaft seals of steam turbines, gas turbines, and air compressors. The gaseous fluids handled in this kind of machinery are often extremely hot, and the shaft speeds are very high. On the other hand, some leakage is normally allowable. This, therefore, is the domain of various non-contacting types of seals that may be referred to as clearance seals or throttling seals. The classical labyrinth is still used in modern turbines and compressors to restrict leakage of steam, air, or combustion gas at the shaft ends and between stages. The thermal expansion coefficient of carbon-graphite is less than that of steel, so the rotor diameter increases more than the carbon ring and could cause the sealing gap to close at high temperature. However, the carbon ring is pre-compressed by a steel bandage so that, due to the expansion of the bandage, the constrained carbon expands more rapidly with temperature than if it were a simple ring.