Wicket gate linkage.
The wicket gate operating linkage consists of the
servomotors, shift ring or operating ring, wicket gate links, and the wicket
gate arms. Although the gate links and gate arms should, in theory, be
interchangeable, they should be matchmarked to their respective wicket
gate and the gates marked according to their installed position. In some
units, the gate link length is adjustable to permit adjustment in the closure
of the wicket gates. Care should be taken not to disturb the adjustment of
these type links to reduce the amount of time required to adjust the wicket
gates during reassembly. Another method of adjusting the wicket gates is
through the use of eccentric pins located either in the shift ring or the gate
arm end of the gate link. The position of each eccentric pin should be
marked to reduce the amount of adjustment during reassembly.
The turbine headcover, because of rust, many times can be
very difficult to break loose. Before trying to lift the headcover, it should
be broken loose using hydraulic jacks between the upper and lower facing
plates. This will eliminate any chance of overstressing the rigging or
bouncing the load with the crane.
Turbine runner and shaft.
With the headeover removed, the turbine
runner and shaft, in most cases, are fairly straightforward to remove.
There is usually a lifting device that attaches directly to the turbine shaft,
and the shaft and runner are simply lifted out of the turbine pit.
IV. INSPECTION AND REPAIR OF UNIT COMPONENTS
Upon removal, all guide and thrust bearings should be thoroughly inspected. Minor
scratches and even some deep gouges can be repaired adequately by carefully
scraping the high spots from the babbitt surface. Extreme care must be taken when
scraping a bearing to prevent removing too much babbitt. Also check the bond
between the babbitt and the bearing shell. Because of the dovetails in the bearing
shell, a guide bearing usually can operate satisfactorily with little physical bond
between the babbitt and the shell, but if there is noticeable separation, it is a good
idea to install the spare bearing or to have the bearing rebabbitted before the unit is
reassembled. Also, when the babbitt is severely damaged by inadequate lubrication
or if the inner diameter of journal bearings is beyond design tolerances, the bearing
should be rebabbitted.
When it is necessary to rebabbit bearings, an American Society for Testing and
Materials (ASTM) B-23, grade 2 or grade 3 tin-based babbitt should be used. Split
shell journal bearings, and if possible segmented shoe guide bearings, should be
rebabbitted by centrifugal casting. Thrust