Brush seals and common issues in brush seal applications

Brush seals are receiving wider acceptance with growing number of successful turbomachinery sealing applications over the past couple of decades. Due to their complaint nature these seals can recover from large transient rotor interference occurrences without any appreciable sustained damage or permanent performance loss. They are formed by a multitude of flexible fine bristles tightly clamped between two metal plates. When subjected to operating pressures and rotor interference, the frictional interactions between thousands of bristles result in very complex seal behavior. Brush seals are known to exhibit load path dependent hysteresis behavior. They also experience increased stiffness under differential pressure loads. While pressure distribution induces some radial forces to close the bristles towards rotor, mechanical interlock and interbristle frictional effects may lead to seal hung up after large rotor interference. In this paper, typical aspects of brush seals are presented. Complex seal behavior and common issues with brush seal applications are also discussed. Recommendations and suggestions for successful seal design are provided.