6.5.1 HP and IP cylinder supports
HP and IP cylinders are fitted with 'paw' supports at each end which rest on the bearing pedestals (Fig 1.102). The paws are horizontal with the palms aligned with the horizontal joint; they are well spaced towards the outer edges of the casing, as they carry the torque reaction from the rotor into the foundations.
In some cases, the paws are part of the lower half casing as illustrated, alternatively they may be part of the upper half, simplifying the casting but necessitating temporary supports for the lower half casing when the halves are unbolted. Vertical guides on the vertical centreline of the rotor act in conjunction with sliding at the paw faces to ensure that the outer casing remains concentric with the bearing pedestal and rotor during expansion. Similar arrangements support the inner casing inside the outer, with paw supports on either side to take the weight and torque reaction, radial keys in the plane of the steam inlets permitting concentric expansion only, and axial keys at the exhaust end allowing for differential axial expansions.
The paw supports of the outer casings contain transverse keys so that the HP and IP casings and bearing blocks expand axially as one unit away from a fixed point between IP and LP cylinders. The axial location between the rotor and the casings is at the thrust bearing between HP and IP cylinders: this arrangement ensures that the close clearances between fixed and moving blades in these cylinders are affected as little as possible by differential axial expansion between rotor and casing on start-up and shutdown.