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 essentially results in a low flow coefficient. The performance of large steam turbines over time 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 to decrease this leakage.