thorough investigation.

[Illustration: FIG. 24]

III. ALLIS-CHALMERS COMPANY STEAM TURBINE

In Fig. 25 may be seen the interior construction of the steam turbine
built by Allis-Chalmers Co., of Milwaukee, Wis., which is, in general,
the same as the well-known Parsons type. This is a plan view showing the
rotor resting in position in the lower half of its casing.

[Illustration: FIG. 25]

Fig. 26 is a longitudinal cross-section cut of rotor and both lower and
upper casing. Referring to Fig. 26 the steam comes in from the
steam-pipe at C and passes through the main throttle or regulating valve
D, which is a balanced valve operated by the governor. Steam enters the
cylinder through the passage E.

Turning in the direction of the bearing A, it passes through alternate
stationary and revolving rows of blades, finally emerging at F and
going out by way of G to the condenser or to atmosphere. H, J, and K
represent three stages of blading. L, M, and Z are the balance pistons
which counterbalance the thrust on the stages H, J, and K. O and Q are
equalizing pipes, and for the low-pressure balance piston similar
provision is made by means of passages (not shown) through the body of
the spindle.

[Illustration: FIG. 26]

R indicates a small adjustable collar placed inside the housing of the
main bearing B to hold the spindle in a position where there will be
such a clearance between the rings of the balance pistons and those of
the cylinder as to reduce the leakage of steam to a minimum and at the
same time prevent actual contact under varying temperature.

At S and T are glands which provide a water seal against the inleakage
of air and the outleakage of steam. U represents the flexible coupling
to the generator. V is the overload or by-pass valve used for admitting
steam to intermediate stage of the turbine. W is the supplementary
cylinder to contain the low-pressure balance piston. X and Y are
reference letters used in text of this chapter to refer to equalizing of
steam pressure on the low-pressure stage of the turbine. The first point
to study in this construction is the arrangement of "dummies" L, M, and
Z. These dummy rings serve as baffles to prevent steam leakage past the
pistons, and their contact at high velocity means not only their own
destruction, but also damage to or the wrecking of surrounding parts. A
simple but effective method of eliminating this difficulty is found in
the arrangement illust