THE KEY TO INSTALLATION
Many different packing ring configurations have been developed which provide adequate flow restriction when in good condition. Most seals, or packing rings, are designed to provide a difficult flow path which essentionally results in a low flow coefficient. The performance of large steam turbines is nearly always compromised by excessive internal leakage that allows steam to bypass one or more stages. There are both design and operating constraints, which influence the type of seal used and the clearances that can be maintained between the rotating and stationary parts.
Proper installation is the key to obtaining the benefits of any type of steam turbine packing available in the Power Generation Industry today. Since the consequences of heavy seal rubs are serious, careful consideration as to how new replacement packing rings will be installed during the next outage, can result in an appreciable less amount of rubbing during start-up and in turn improve unit efficiency. To ensure the proper installation of packing, attention must be given to the following:
The magnitude of the losses associated with worn packing rings of any design can become large and the costs related to a reduction in performance are large enough to warrant having complete distortion awareness measurements taken to maintain control of the final seal clearances, which in turn, help in minimizing the associated losses.
Upper Half Pins and Retaining Keys
It is important during installation that the retaining pin or key slots on the upper half packing segments are machined properly; allowances for required axial and radial clearance, must be taken into consideration for the packing rings to operate correctly. Restriction of movement can result in excessive radial clearances due to heavy rubbing.