Page 184 - Steam Turbines Design, Applications, and Rerating

Couplings and Coupling Considerations 163

9.6 Axial Thrusts
In the turbine as well as in the compressor or other connected machine
relatively high axial thrust forces must be absorbed by suitably
designed tilting pad axial thrust bearings.
The rigid connection between turbine and driven equipment shafts
allows the axial forces of both turbine and driven machine to be
absorbed by only one axial thrust bearing. The axial thrusts of both
machines are in opposite directions, so that the thrust bearing only has
to absorb the resulting differential thrust.
Gear type couplings are expected to slide when axial forces are
applied. For this reason the driven machine and the turbine must each
be equipped with an axial thrust bearing.

9.7 Limits of Application

Flexible couplings at higher torques and speeds soon reach a technical
limit for application. Beyond that there is only the rigid coupling.There
is no other acceptable solution. However, the operational results of
multishaft machines with rigid couplings up to 1350 MW show that
properly designed equipment will perform flawlessly for decades.