Large FCCU blower stonewalled durring start-up after T/a. Blower is part of the expander train with helper turbine. During Stonewall blower became unstabe and aerodynamicaly imbalanced. Imbalance caused rotor to rub. Rubs usually change amplitude and phase against rotation but this machine changed with rotation, hmmm. It first started at 45 deg and amplitude and phase started to grow against rotation, 8 minutes later direction of phase reversed and went around 360 deg (polar plot). It eventualy came back to it's original position. The orbit shows the flat spots on top. This rotor has a normal shaft centerline rise of 9 mils, which could have something to do with direction of phase change.

This message has been edited. Last edited by: Erik Concha,