Page 70 - Introduction to Marine Engineering

Steam turbines and gearing 57

Curtis. An impulse turbine with more than one row of blades to each
row of nozzles, i.e. velocity compounded.
De Laval, A high-speed impulse turbine which has only one row of
nozzles and one row of blades.
Rateau. An impulse turbine with several stages, each stage being a row
of nozzles and a row of blades, i.e. pressure compounded.

Marine steam turbines are required to be reversible. This is normally
achieved by the use of several rows of astern blading fitted to the
high-pressure and low-pressure turbine shafts to produce astern
turbines. About 50% of full power is achieved using these astern
turbines. When the turbine is operating ahead the astern blading acts as
an air compressor, resulting in windage and friction losses.

Turbine construction

The construction of an impulse turbine is shown in Figure 3.5. The
turbine rotor carries the various wheels around which are mounted the
blades. The steam decreases in pressure as it passes along the shaft and
increases in volume requiring progressively larger blades on the wheels.
The astern turbine is mounted on one end of the rotor and is much

Caring

Attem turbine

Bearing

Diaphragm
Exhauftfteam
Figure 3.5 Impulse turbine