TAYLOR DEVICES’ FRICTIONLESS HERMETIC DAMPER Taylor Devices, a 50 year old manufacturer of damping products, proposed a unique solution to the damper design requirements for the Millennium Bridge.  To address the various design issues, a unique and patented damper was proposed, previously used exclusively by NASA and other U.S. Government agencies for space based optical systems. These previous applications had similar requirements for long life and high resolution at low amplitudes, but required relatively low damper forces from small, lightweight design envelopes.  Figure 4 is a photograph of a typical damper of this design, used in space on more than 70 satellites to protect delicate solar array panels.  Figure 4 also shows the most unique element of this design, a frictionless seal made from a welded metal bellows.  This type of seal does not slide, but rather flexes without hysteresis as the damper moves. A cutaway of a typical Frictionless Hermetic Damper is shown in Figure 5.  Two metal bellows seals  are used to seal fluid in the damper.  As the damper moves, the two metal bellows alternately extend and retract, by flexure of the individual bellows segments.  Since the seal element elastically flexes rather than slides, seal hysteresis is nearly zero. The volume displaced by the compressing bellows passes through the crossover ports to the extending bellows at the opposite end of the damper.  While this is occurring, damping forces are being produced by orifices in the damping head, and the pressures generated are kept isolated from the metal bellows by high restriction hydrodynamic labyrinth bushings.  Because hydrodynamic bushings are used, no sliding contact with the piston rod occurs, assuring frictionless performance. FIGURE 4 SPACE SATELLITE DAMPER To adapt this basic design to the Millennium Bridge largely involved simply scaling the small satellite dampers to the required size range.  All parts, including the metal bellows, were designed with low stress levels to provide an endurance life in excess of 2 x 10⁹ cycles.  The metal bellows and other moving parts were constructed from stainless steel for corrosion resistance. A total of 37 dampers were constructed, of 7 different types, and are listed in Figure 6.