TURBINE VANES 295
Call the velocity acquired by the steam as a result of the
expansion in the passages of any one row of vanes. Then, since
steam enters each set of guide passages with an initial velocity
equal to the velocity v of the steam leaving the wheel vanes, we
have Velocity of steam leaving the guide vanes=v+u.
In the moving vanes the velocity 1 acquired through expansion
has the effect of increasing the velocity of the steam relative to
the vanes, so that relative velocity r of steam leaving the moving
vanes R+u. From the foregoing we therefore have, V-v=
-R, or the difference between the absolute velocities and v
equals the difference between the relative velocities r and R.
Moving Vanes
B
Guides
283
20
Goldes
Fig. 10.
Construction of a Reaction Diagram.-In Fig. 10, where the
guide and moving vanes are alike, it will be evident that angles
A and B must be equal and angles C and D equal, to secure tan-
gential action upon the vanes. Hence, in Fig 11 we make these
angles equal, having A and B as small as practicable and making
angles C and D from 70 to 90 degrees. In hydraulic work 90 de-
grees is frequently selected for this angle.
Referring to triangles (1) and (2), Fig. 11, we have the com-
mon side w and angles A and B equal; consequently these trian-
gles are equal and Vr and R-v. Having assumed a suitable
value for w, and knowing the angles, the other sides may be cal-
culated by the principle in trigonometry that in any triangle the
