Page 55 - Steam Turbines Design, Applications, and Rerating

36 Chapter Two

Figure 2.9 Valve casing (valve chest) assembly. (Asea Brown Boveri, Baden, Switzerland)

There are a number of fabrication methods available for nozzle rings.
Elliott is one of several companies whose first-stage nozzle rings are
often made by milling steam passages into stainless steel blocks, which
are then welded together (Fig. 2.10).
The nozzles in the intermediate pressure stages are formed from
stainless steel nozzle sections and inner and outer bands. These are
then welded to a round center section and an outer ring.
Low-pressure diaphragms of condensing turbines are sometimes
made by casting the stainless nozzle sections directly into high-strength
cast iron. This design includes a moisture catcher to trap condensed
droplets of water and keep them from reentering the steam path. These
diaphragms can also be completely fabricated.

2.3 Steam Turbine Diaphragms
and Labyrinth Packing
A diaphragm in an impulse turbine is a stationary partition located
between each rotating wheel that