The Horizontal Steam Turbine For Stationary Plants 1920
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Mixed Pressure Turbines
Mixed pressure turbines are designed to
operate with two sources of steam supply,
a low pressure source and a high pressure
source. They may be low pressure turbines
with additional blacling to utilize high pres-
sure steam in case the supply of exhaust
steam is not sufficient for the load required;
or they may be high pressure turbines
Fig. i. The Principle of the Impulse Type Turbine.
specially designed to make additional use of
a supply of low pressure steam.
TYPES
Horizontal type turbines are of the im-
pulse type, the reaction type, or combine the
features of both.
The Impulse Type Turbine
All expansion of steam takes place in
stationary nozzles or steam delivery pipes
and the velocity energy thus produced acts
directly on the blades of the revolving disk.
The principle of the impulse type turbine
is illustrated in Fig. i.
The high velocity steam from the nozzle
(H) impinges on the buckets (F7) of the
wheel (F6) revolving it at high, speed.
Steam economy is secured with high velocity
of the turbine wheel.
The capacity of this type of turbine is in-
creased either by repassing the steam through
another and larger set of buckets arranged in
a circular section inside the row of buckets on
the edge of the turbine wheel, or by the addi-
tion of one or more bucket wheels, which
utilize the steam flow after it has passed
through the set of buckets fixed in the rim
of the first wheel.
Single-stage impulse type turbines are
built in sizes below 600 hp.
Multi-stage impulse type turbines are
built in sizes from 500 hp. to 6,000 hp.
The Reaction Type Turbine
The steam acts both on the moving and
the stationary buckets or blades. As it
passes through the turbine the steam im-
parts a small part of velocity energy by im-
pulse at entrance and the greater part by the
reactive thrust of expansion, on the blades
fixed in the periphery of the revolving rotor.
The pressure of steam expansion is more
effective than the velocity flow at which it
impinges on the blades.
The larger size turbines are of the re-
action type and operate at speeds as high as
3,600 revolutions per minute.
The De Laval, Kerr, Terry, Moore, Par-
sons, Curtis, Zoelly, Riedler-Stumpf, Brown,
Bovery, A.E.G.,M.A.N., Allis-Chalmers-
Rateau, etc.? are adaptations or combina-
tions of the impulse or reaction types.
Curtis turbines are both vertical and hori-
zontal .
The differences in design of all horizontal
turbines affect only the arrangement of the
revolving and stationary disks, the blacling
and the steam distribution to the disks; they
do not influence the construction of the main
bearings nor the methods of lubrication.
CONSTRUCTION
The Impulse Type of Turbine
The impulse type of turbine consists of a
wheel case of iron. (A, Fig. 3), cast in two
parts, and a rotor (Fig. 2).
The Rotor
The turbine spindle or shaft is short and of
relatively small diameter, but stiff enough
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