Guide bearing and seal ring clearances
.-Clearance readings should
be taken on all guide bearings at least in four quadrants. On segmented
shoe guide bearings, check the clearance of each bearing shoe. Top
and bottom seal ring clearance should also be taken.
Generator air gap.-Air gap readings should be taken at least in four
quadrants and at the top and bottom of the rotor. For better accuracy
in determining the position of the rotor in the stator and for determining
the shape of the stator, more readings may be required.
Shaft alignment readings.- Preteardown alignment readings may be
taken with or without the guide bearings in place. With the bearings in
place, the bearing centers can be plotted to determine their
concentricity, but the shaft itself will not be free, and the shaft's actual
straightness may not be represented by readings. With the bearings and
the packing removed, the shaft should be hanging free, and the readings
should represent the condition of the shaft, but the operating position
of the shaft and bearings will not be known. If the bearings are
removed, a check of the static shaft runout should be made.
Labeling and match marking
Prior to removal, most parts should be match marked to make sure they are
installed in exactly the same position from which they were removed. This is
especially important for parts that can be rotated, such as thrust block keys, or
for parts such as wicket gates, that can be interchanged. Many parts are
marked during the original assembly. If these markings are visible and their
meanings are clear, no more marks should be made. If new match marks or
labels are made, the original markings should be completely removed so there
is no confusion during reassembly.
It is important during disassembly to check the manufacturer's drawings
carefully to make sure all parts are removed in the correct order and that all
fasteners, piping connections, and wiring are removed. It is also important that
the various crafts coordinate their activities so that there is no unanticipated
delays due to the unavailability of personnel.
The list of weights and a rigging manual should be consulted often during
disassembly., The weight of any part should never be "guessed," and the
rigging should never be assumed to be strong enough. A part may be much
heavier than it appears, and rigging, due to sling angles or other