Stators

As already described, the stators may be carried in a separate inner casing or may be carried by the outer, center section of the main casing. When movable stator vanes are used, the vanes pass through the wall of the carrier. The outer side of the casings exposes the shank ends, which are used as shafts to connect to the linkage that will control the movement. Because of leakage at the mounting bushings in the stator liner or earner, the single-case unit has some sealing problems, which are inherently taken care of in the double-case construction. The single-case construction uses a lagging over the linkage, which can act as a collector.

For non-movable construction, some vendors use a conical shank and bolt arrangement. The stator vanes are set to a gauge at the factory and locked in place by tightening the hold-down nut and then staking. This construction permits flexibility for capacity adjustment at relatively low cost because the vane stagger can be reset without the manufacture of new parts or a complete machine disassembly. Other bolting arrange ments are manufactured to give the same flexibility as the conical shanks. Some designs use a more permanent fixture for the stator vanes, setting the vanes in a diaphragm similar to the steam turbine or fixing the vane to the stator casing by dovetailing.

The stator vanes are usually not shrouded. This is not a hard and fast rule, in practice, often vanes are mixed with some shrouded and some unshrouded. When a separate stator inner case is used, it is normally of cast iron. If the temperature is expected to exceed 500°F, the liner will be multipart with the discharge end being made of steel.

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