rated in this figure. The two smaller balance
pistons, L and M, are allowed to remain on the high-pressure end; but
the largest piston, Z, is placed upon the low-pressure end of the rotor
immediately behind the last ring of blades, and working inside of the
supplementary cylinder W. Being backed up by the body of the spindle,
there is ample stiffness to prevent warping. This balance piston, which
may also be plainly seen in Fig. 25, receives its steam pressure from
the same point as the piston M, but the steam pressure, equalized with
that on the third stage of the blading, X, is through holes in the webs
of the blade-carrying rings. Entrance to these holes is through the
small annular opening in the rotor, visible in Fig. 25 between the
second and third barrels. As, in consequence of varying temperatures,
there is an appreciable difference in the endwise expansion of the
spindle and cylinder, the baffling rings in the low-pressure balance
piston are so made as to allow for this difference. The high-pressure
end of the spindle being held by the collar bearing, the difference in
expansion manifests itself at the low-pressure end. The labyrinth
packing of the high-pressure and intermediate pistons has a small axial
and large radial clearance, whereas the labyrinth packing of the piston
Z has, vice versa, a small radial and large axial clearance. Elimination
of causes of trouble with the low-pressure balance piston not only makes
it possible to reduce the diameter of the cylinder, and prevent
distortion, but enables the entire spindle to be run with sufficiently
small clearance to obviate any excessive leakage of steam.

Detail of Blade Construction

In this construction the blades are cut from drawn stock, so that at its
root it is of angular dovetail shape, while at its tip there is a
projection. To hold the roots of the blades firmly, a foundation ring is
provided, as shown at A in Fig. 27. This foundation ring is first formed
to a circle of the proper diameter, and then slots are cut in it. These
slots are accurately spaced and inclined to give the right pitch and
angle to the blades (Fig. 28), and are of dovetail shape to receive the
roots of the blades. The tips of the blades are substantially bound
together and protected by means of a channel-shaped shroud ring,
illustrated in Fig. 31 and at B in Fig. 27. Fig. 31 shows the cylinder
blading separate, and Fig. 27 shows both with the shrouding. In these,
holes are p