Patent ID: 6896482

Claim:
A steam turbine comprising: an outer housing; a turbine shaft rotatably supported in said outer housing; and a plurality of turbine stages located along said turbine shaft and contained within said outer housing, each said turbine stage comprising: a diaphragm attached to the casing, said diaphragm comprising a plurality of nozzles; a rotor fixedly attached to said turbine shaft, said rotor comprising a plurality of buckets and a bucket cover; and a packing ring mounted in a first circumferentially extending groove in said diaphragm, said packing ring comprising a seal shroud and a sealing means, said packing ring positioned adjacent said turbine shaft to provide a seal in a gap between said turbine shaft and said diaphragm; said seal shroud fabricated from a first material having a first coefficient of expansion, said diaphragm fabricated from a second material having a second coefficient of expansion, said first and second materials selected so that at a first temperature said gap between said turbine shaft and said diaphragm is larger than at a second higher temperature.