PRINCIPLES OF NAVAL ENGINEERING 



38.79X 

 Figure 12-12.— Velocity-compounded impulse 

 turbine (one Curtis stage). 



TURBINE COMPONENTS 

 AND ACCESSORIES 



Propulsion turbine components and acces- 

 sories include foundations, casings, nozzles (or 

 the equivalent stationary blading), nozzle dia- 

 phragms, rotors, blades, bearings, shaft glands, 

 gland seals, oil seal rings, dummy pistons and 

 cylinders (on some reaction turbines), flexible 

 couplings, reduction gears, lubrication systems, 

 and turning gears. 



Turbine Foundations 



Foundations for propulsion turbines are built 

 up from strength members of the hull so as to 

 provide a rigid supporting base. The after end 

 of the turbine is secured rigidly to the struc- 

 tural foundation. The forward end of the turbine 

 is secured in such a way as to allow a slight 

 freedom of axial movement which allows the 

 turbine to expand and contract slightly with 

 temperature changes. 



The freedom of movement at the forward 

 end is accomplished by one of the two methods. 

 Elongated bolt holes or grooved sliding seats 

 may be used to permit the forward end to slide 

 slightly fore-and-aft, as expansions and con- 

 traction occur. Or the forward end may be 

 secured to a deep flexible I-beam (fig. 12-15) 

 installed with its longitudinal axis lying athwart- 

 ship. When the turbine is cold, this I-beam is 

 deflected slightly aft from the vertical position. 

 When the turbine is operating at maximum 

 power, the I-beam is deflected forward. This 



arrangement results in minimum stresses in 

 the I-beam over the complete range of turbine 

 expansion. The fixed end of the turbine is aft, 

 so the motion resulting from expansion cannot 

 be transmitted to the reduction gears, where 

 distortion and serious damage would occur if 

 the after end of the turbine were free to move. 

 Steam lines connected to the turbines are 

 curved, as shown in figure 12-15, to allow for 

 expansion of the steam line and avoid un- 

 acceptable strains on turbine casings that could 

 cause distortion or misalignment. 



Turbine Casings 



Casings for propulsion turbines are divided 

 horizontally to permit access for inspection and 

 repair. Flanged joints on casings are accurately 

 machined to make a steamtight metal-to-metal 

 fit, and the flanges are bolted together. Some 

 high pressure turbine casings are also split 

 vertically to facilitate manufacture, particularly 

 when different alloys are used for the high 

 temperature inlet end and the lower temperature 

 exhaust end. However, these vertical joints are 

 never unbolted and they are usually seal welded. 



Each casing has a steam chest to receive the 

 incoming steam and deliver it to the first-stage 

 nozzles or blades. An exhaust chamber receives 

 the steam from the last row of moving blades 

 and delivers it to the exhaust connection. Open- 

 ings in the casing include drain connections, 

 steam bypass connections, and openings for 

 pressure gages, thermometers, and relief 

 valves. 



Nozzles 



As previously discussed, the function of a 

 nozzle is to convert the thermal energy of the 

 steam into mechanical kinetic energy. Its sec- 

 ondary function is to direct the steam to the 

 turbine blades. Some turbines have a full arc 

 admission of steam; in this case, the first 

 stage nozzles extend around the entire circle 

 of the first row of blades. Other turbines have 

 partial arc admission; in this case, only a 

 section of the blade circle is covered by the 

 nozzles. In general, the arrangement of nozzles 

 in any turbine depends upon the range of power 

 requirements and upon a number of design 

 factors. 



A nozzle is essentially an opening or a 

 passageway for the steam. When we speak 

 of nozzle construction or arrangement, 



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