Patent ID: 7186074

Claim:
An axial flow steam turbine comprising: (a) at least one impulse turbine stage having an annular row of static blades extending between a radially outer static ring and a radially inner static ring and an annular row of moving blades provided with blade root portions; (b) a rotor drum having a plurality of peripherally extending slots, the blade root portions of the moving blades being held in the peripherally extending slots; (c) a sealing device acting between the inner static ring and the rotor drum; and (d) a turbine casing surrounding the impulse turbine stage and having a recess, the outer static ring being axially located in the recess and having greater thermal inertia and greater stiffness than the inner static ring, the outer static ring being capable of a limited radial movement relative to the turbine casing so as to thereby accommodate an out-of-round distortion of the turbine casing relative to the outer static ring, wherein the rotor drum includes an annular recess axially spaced from the peripherally extending slots and having a radial depth less than that of the peripherally extending slots, wherein the sealing device extends into the annular recess so that a radial extent of the sealing device is disposed at least partly within an outer envelope of the drum rotor, and wherein a radially inner portion of the inner static ring projects into the annular recess.