Conventional labyrinth seals are segmented and positioned by radial flat springs. Retractable packing replaces the flat springs with coil springs between the segments to enlarge shaft clearances during start-up in order to avoid damage caused by thermal distortion and vibration as the unit passes through its critical speed zone. As shown in the figure 1 below, the coil spring at the end of each seal segment holds the segment away from the shaft during start-up. At steady state condition, high pressure steam enters the ring segments to restore design clearance for normal operation at the design clearances.

The retractable seal provides reliability improvements by making starts smoother and eliminating contact during start-up. Fewer rubs translates into less maintenance on the seals. The smaller clearances improves performance, sustains heat-rate, and reduces degradation.

FIGURE 1 – RETRACTABLE SEAL SEGMENT AND COIL SPRING