or diameter of
the rotor; in the passage C after it has passed the second section. The
pressure acting upon the exposed faces of the rows of vanes would crowd
the rotor to the left. They are therefore balanced by pistons or
"dummies" P P P revolving with the shaft and exposing in the annular
spaces B^1 and C^1 the same areas as those of the blade sections which
they are designed to balance. The same pressure is maintained in B^1 as
in B, and in C^1 as in C by connecting them with equalizing pipes E E.
The third equalizing pipe connects the back or right-hand side of the
largest dummy with the exhaust passage so that the same pressure exists
upon it as exists upon the exhaust end of the rotor. These dummy pistons
are shown at the near end of the rotor in Fig. 35. They are grooved so
as to form a labyrinth packing, the face of the casing against which
they run being grooved and brass strips inserted, as shown in Fig. 39.
The dummy pistons prevent leakage from A, B^1 and C^1 to the condenser,
and must, of course, run as closely as practicable to the rings in the
casing, the actual clearance being from about 0.005 to 0.015 of an inch,
again depending on the size of the machine.

[Illustration: FIG. 39]

The axial adjustment is controlled by the device shown at T in Fig. 34
and on a larger scale in Fig. 40. The thrust bearing consists of two
parts, T{1} T{2}. Each consists of a cast-iron body in which are placed
brass collars. These collars fit into grooves C, turned in the shaft as
shown. The halves of the block are brought into position by means of
screws S{1} S{2} acting on levers L{1} L{2} and mounted in the bearing
pedestal and cover. The screws are provided with graduated heads which
permit the respective halves of the thrust bearing to be set within one
one-thousandth of an inch.

[Illustration: FIG. 40]

The upper screw S{2} is set so that when the rotor exerts a light
pressure against it through the thrust block and lever the grooves in
the balance pistons are just unable to come in contact with the dummy
strips in the cylinder. The lower screw S{1} is then adjusted to permit
about 0.008 to 0.010 of an inch freedom for the collar between the
grooves of the thrust bearing.

These bearings are carefully adjusted before the machine leaves the
shop, and to prevent either accidental or unauthorized changes of their
adjustment the adjusting screw heads are locked by the method shown in
Fig. 40. The screw cannot be