(6b) On the Application of Advanced Pressure Actuated Seals in Legacy Turbomachinery

Seal technology for reduced shaft leakage continues to be developed and utilized in turbomachinery for improved performance. This lecture is focused on the consideration of retrofitting legacy equipment with advanced shaft sealing to recover performance and extend efficient operation. Several sealing concepts benefit from system pressure to close operating seal clearance. Of these, the Pressure Actuated Leaf Seal (PALS) is particularly attractive for retrofit in legacy equipment where misalignment and distortion are present. Installation of fixed seals require larger clearance to avoid rubs where there is ovality. The lecture will discuss PALS design for out of round conditions in which material is provided for sacrificial leaf tip wear-in on initial startup, similar to an abradable seal. Subsequent operating clearance is non-contacting and clearance approaches rotor run-out for greatly reduced seal leakage. Startup and shut-down rubs are avoided by flexure of PALS leaves on their support in response to differential pressure. Leaf tip closure with pressure is designed to provide clearance passing through transient thermal distortion and critical speeds. PALS configuration options are flexible to accommodate available seal space. PALS are robust in that they can ride over surface discontinuities making them a strong candidate for blade tip shroud sealing.