Page 178 - Steam Turbines Design, Applications, and Rerating

Chapter
9

Couplings and Coupling

Considerations

There are numerous coupling types and configurations available in the
marketplace. However, from practical and reliability-oriented points of
view the overall selection narrows down quickly to just a few types.
These are described below; for additional details, please refer to our
companion text, A Practical Guide to Compressor Technology.
In principle there are two possibilities: the flexible coupling and the
rigid coupling. Flexible couplings for steam turbines are further subdi-
vided into lubricated and nonlube types. Finally, nonlube types could
incorporate one or more flexing metallic disks or, in the case of small
turbines, elastomeric flexing elements. The three principal coupling
types of interest are shown in Fig. 9.1.

9.1 Power Transmission
The diaphragm coupling (Fig. 9.1a) is a worthy replacement of the
older gear coupling. This is indicated by comparing the selection crite-
ria of Table 9.1.
The gear coupling transmits the torque through the gear teeth of the
flange halves and the coupling sleeve (Fig. 9.1b). This coupling design
allows a certain degree of misalignment between the shafts and also
some eccentricity of the turbine and compressor shafts. In addition,
gear couplings can accommodate a certain amount of axial displace-
ment of both shafts relative to one another. These compensating char-
acteristics are the only reason why gear couplings are in use because,
on the other hand, this type is more complicated than the rigid cou-
pling and is limited in its application.

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