e clearances allowed can be gaged by a feeler placed between a ring
and the groove wall. Before a test the spindle should be turned slowly
around, the feelers being kept in position. By this means any mechanical
flaws or irregularities in the groove walls may be detected.

[Illustration: FIG. 61]

It has sometimes been found that the groove walls, under the combined
action of superheated steam and friction, in cases where actual running
contact has occurred, have worn very considerably, the wear taking the
form of a rapid crumbling away. It is possible, however, that such
deterioration may be due solely to the quality of the steel from which
the spindle is forged. Good low-percentage carbon-annealed steel ought
to withstand considerable friction; at all events the wear under any
conditions should be uniform. If the surfaces of both rings and grooves
be found in bad condition, they should be re-ground, if not sufficiently
worn to warrant skimming up with a tool.

As the question of dummy leakage is of very considerable importance
during a test, it may not be inadvisable to describe the manner of
setting the spindle and cylinder relatively to one another to insure
minimum leakage, and the methods of noting their conduct during a
prolonged run. In Fig. 62, showing the spindle, B is the thrust (made in
halves), the rings O of which fit into the grooved thrust-rings C in the
spindle. Two lugs D are cast on each half of the thrust-block. The
inside faces of these lugs are machined, and in them fit the ball ends
of the levers E, the latter being fulcrumed at F in the thrust-bearing
cover. The screws G, working in bushes, also fit into the thrust-bearing
cover, and are capable of pushing against the ends of the levers E and
thus adjusting the separate halves of the block in opposite directions.

[Illustration: FIG. 62]

The top half of the turbine cylinder having been lifted off, the spindle
is set relatively to the bottom half by means of the lower thrust-block
screw G. This screw is then locked in position and the top half of the
cover then lowered into place. With this method great care must
necessarily be exercised when lowering the top cover; otherwise the
brass dummy rings may be damaged.

A safer method is to set the dummy rings in the center of the grooves of
the spindle, and then to lower the cover, with less possibility of
contact. There being usually plenty of side clearance between the blades
of a turbine, it