Brush seals and combined labyrinth and brush seals for rotary machines

Abstract

Brush seals are retrofitted into existing turbine labyrinth seal rings to create a fail-safe seal design at locations wherever labyrinth seals are currently used, including interstage shaft seals, rotor end seals, bucket (or blade) tip seals and spill strips. Brush seals, per se, when used in place of labyrinth seals, can result in considerable span reductions of steam turbines, or machines with more turbine stages for a given span. Application to end packings results in the potential elimination of gland sealing/exhauster systems. Brush seal life can be improved by retrofitting brush segments to labyrinth seal segments that are either spring-backed, or use pressure loads to obtain design clearances only after steady state operating conditions are achieved. The brush seals are provided with backing plates shaped like labyrinth teeth, resulting in a fail-safe design. Also, the use of existing labyrinth teeth as bristle backing plates results in a brush seal with diminished susceptibility to hysteresis when compared to conventional brush seal designs. Low friction coatings can also be used to reduce brush seal hysteresis. Incorporation of brush seals in labyrinth seal rings that are either spring-backed or held in place by pressure forces results in extremely low brush seal wear.