Chapter 16. -AUXILIARY STEAM TURBINES 



pressure which is approximately 15 psig on oil- 

 fired ships and somewhat higher on nuclear 

 ships. 



Most auxiliary turbines are axial flow units 

 which are quitesimilar (except for size and num- 

 ber of stages) to the axial-flow propulsion tur- 

 bines described in chapter 12. However, some 

 auxiliary turbines are designed for helical flow 

 and some for radialflow— types of flow which are 

 seldom if ever used for propulsion turbines. 



A helical-flow auxiliary turbine is shown in 

 figure 16-1. In a turbine of this type, steam 

 enters at a tangent to the periphery of the rotor 



and impinges upon the moving blades. These 

 blades, which . consist of semicircular slots 

 milled obliquely in the wheel periphery, are 

 called buckets . The buckets are shaped in such a 

 way that the direction of steam flow is reversed 

 in each bucket, and the steam is directed into a 

 redirecting bucket or reversing chamber 

 mounted on the inner cylindrical surface of the 

 casing. The direction of the steam is again re- 

 versed in the reversing chamber, and the con- 

 tinuous reversal of the direction of flow keeps 

 the steam moving helically. 



Several nozzles are usually installed in this 

 type of turbine, and for each nozzle there is an 

 accompanying set of redirecting buckets or re- 

 versing chambers. Thus the reversal of steam 

 flow is repeated several times for each nozzle 

 and set of reversing chambers. 



Now let us consider the classification of a 

 helical-flow turbine with respect to staging and 

 compounding, as discussed in chapter 12. It is 

 a single-stage turbine because it has only one 

 set of nozzles and therefore only one pressure 

 drop. It is a velocity-compound turbine because 

 the steam passes through the moving blades 

 (buckets) more than once, and the velocity of the 

 steam is therefore utilized more than once. The 

 helical-flow turbine shown in figure 16-1 might 

 be said to correspond roughly to a turbine in 

 which velocity- compounding is achieved by the 

 use of four rows of moving blades. 



Helical-flow auxiliary turbines are used for 

 driving some pumps and forced draft blowers. 



The arrangement of nozzles and blading that 

 provides radial flow in a turbine is shown in fig- 

 ure 16-2. Turbines of this type are sometimes 

 used for driving auxiliary units such as pumps. 



As discussed in chapter 12, turbines may be 

 classified as single- entry or re-entry turbines, 

 depending upon the number of times the steam 

 enters the blading. All multistage (and hence all 



33.45X 



38.81X 



Figure 16-1.— Helical-flow turbine. 



Figure 16-2.— Radial flow. 



423 



