290 STEAM TURBINES
in the body a, working with higher pressure has a smaller, and in the body b,
working with lower pressure, a larger diameter. The two turbine bodies a and
Fig. 539.
b are attached to a shaft c in the case d. The thrust-bearing of this shaft is
denoted by n. The steam enters through a branch e, streams through the tur-
bine section a, and leaves it by the over-
flow channel to pass through the pipe
k, which is provided with a governing
valve, into the entrance channel h of
the body b. The latter is traversed in
a direction opposite to that of the
body a by steam of low pressure, which
leaves the compound turbine by the ex-
haust i. By means of pressure vanes
on the one end wall of the body b,
and leading channels on the end wall
of the case d, which is arranged as a
discharge channel i, a turbine is formed for backwards motion, which, in the
application of this engine; for the propulsion of ships, is a necessity. The fresh
steam here streams through the inlet pipe m to the smallest of the concentric
turbine wreaths, and passes from the largest of these into the exhaust channel i.
During forward motion this backwards turbine i runs free without injurious
action in the reduced pressure of the outflowing steam. Fig. 539 shows the
arrangement of a steam turbine in which the body a as well as the body b is
provided with several discs fitted in the case d on the shaft c, and bearing wreaths
on both sides. Through the entrance branch e the steam first proceeds to the
smallest disc of the turbino body a, and passes onward to the larger disc. Thence
it streams through the overflow channel f, which is provided with a governing
valve g, and through the pipe into the entrance channel h of the low pressure
turbine body b, and leaves the latter through the outflow channel i. Here also a
backwards motion turbine forms part of the arrangement. It would, of course, be
feasible in like manner to combine more than two turbine bodies for the same
purpose, and to make use of separate cases. In the particular case of a turbine
employed as a marine engine, it will be of advantage so to chose the diameter of the
turbine body of the compound engine that when the latter is in motion a pressure
opposed to the axial one of the propeller acts in the direction of the shaft, so that
the thrust-bearing n is strained as little as possible. This axial pressure is, in the
application of the turbine alluded to, directed in the backwards direction, and its
amount must be so chosen that it is approximately equal to the forward thrust of
the propeller. The governing valve g in the overflow channel is intended, if
necessary, to detain a part of the steam issuing from the turbine body a, so that
behind this latter the pressure of the steam increases, while the pressure of the
steam that streams through the free opening of the valve to the turbine body b is
reduced. By means of an adjustment of this governing valve g the resultant axial
