and energy are more or less completely abstracted and
appropriated by the revolving member. The Parsons turbine utilizes a
combination of these two methods.

[Illustration: FIG. 34]

Fig. 34 is a sectional view of the standard Westinghouse-Parsons
single-flow turbine. A photograph of the rotor R R R is reproduced in
Fig. 35, while in Fig. 36 a section of the blading is shown upon a
larger scale. Between the rows of the blading upon the rotor extend
similar rows of stationary blades attached to the casing or stator. The
steam entering at A (Fig. 34), fills the circular space surrounding the
rotor and passes first through a row of stationary blades, 1 (Fig. 37),
expanding from the initial pressure P to the slightly lower pressure
P{1}, and attaining by that expansion a velocity with which it is
directed upon the moving blade 2. In passing through this row of blades
it is further expanded from pressure P{1} to P{2} and helps to push the
moving blades along by the reaction of the force with which it issues
therefrom. Impinging upon the second row of stationary blades 3, the
direction of flow is diverted so as to make it impinge at a favorable
angle upon the second row of revolving blades 4, and the action is
continued until the steam is expanded to the pressure of the condenser
or of the medium into which the turbine finally exhausts. As the
expansion proceeds, the passages are made larger by increasing the
length of the blades and the diameter of the drums upon which they are
carried in order to accommodate the increasing volume.

[Illustration: FIG. 35]

[Illustration: FIG. 36]

[Illustration: FIG. 37]

It is not necessary that the blades shall run close together, and the
axial clearance, that is the space lengthwise of the turbine between the
revolving and the stationary blades, varies from 1/8 to 1/2 inch; but in
order that there may not be excessive leakage over the tops of the
blades, as shown, very much exaggerated, in Fig. 38, the radial
clearance, that is, the clearance between the tops of the moving blades
and the casing, and between the ends of the stationary blades and the
shell of the rotor, must be kept down to the lowest practical amount,
and varies, according to the size of the machine and length of blade,
from about 0.025 to 0.125 of an inch.

[Illustration: FIG. 38]

In the passage A (Fig. 34) exists the initial pressure; in the passage B
the pressure after the steam has passed the first section