PRINCIPLES OF NAVAL ENGINEERING 



propulsion) turbines are of the single- entry- 

 type. However, some auxiliary turbines are of 

 the re-entry type. 



Re-entry turbines are those in which the 

 steam passes more than once through the blading. 

 Hence the helical-flow turbine just discussed is 

 a re-entry turbine. A different kind of re-entry 

 turbine is shown in figure 16-3. This turbine is 

 similar in principle to the helical-flow turbine, 



38.82X 

 Figure 16-3.— Re-entry turbine with one revers- 

 ing chamber. 



but it has one large reversing chamber instead 

 of a number of redirecting chambers. Re-entry 

 turbines are sometimes made with two revers- 

 ing chambers instead of one. 



The auxiliary turbine shown in figure 16-4 

 is used to drive main condensate pumps, feed 

 booster pumps, and lubricating oil service pumps 

 on many older destroyers. Note that this is a 

 radial-flow turbine. This same design of turbine 

 is used on some newer ships, but with improved 

 metals designed to withstand higher pressures, 

 higher temperatures, and high-impact (HI) 

 shock. 



Another kind of auxiliary turbine is shown in 

 figure 16-5. This turbine, which is usedtodrive 

 main condenser circulating pumps, is a verti- 

 cally mounted, axial-flow, velocity- compounded 

 impulse turbine. Although this type of turbine is 

 becoming obsolete, it is still in operation on 

 some older types of ships. The turbine shaft is 

 secured to the vertical shaft of the pump. A thrust 

 bearing, mounted integrally with tlie upper radial 

 bearing, carries the weight of the rotating ele- 



ment and absorbs any downward thrust. A throttle 

 valve and a double- seated balanced inlet valve 

 (normally held wide open by the governor mech- 

 anism) admit steam to the turbine. 



Figure 16-6 shows an auxiliary turbine used 

 to drive a 400-kilowatt a-c, 50-kilowatt d-c 

 ship's service turbogenerator. The turbine is an 

 axial-flow, pressure- compounded unit. It ex- 

 hausts to a separate auxiliary condenser which 

 has its own circulating pump, condensate pump, 

 and air ejectors. Cooling water for the condenser 

 is provided by the auxiliary circulating pump, 

 through separate injection and overboard valves. 

 In case of casualty to the auxiliary condenser, 

 the turbine can exhaust to the main condenser 

 when the main plant is in operation. 



The turbogenerator turbine shown in figure 

 16-6 is so designed that it can operate on either 

 saturated steam or superheated steam. Provi- 

 sion is made for supplying steam to the turbine 

 either from the main steam line (superheated) 

 while under way or from the auxiliary steam line 

 (saturated) during in-port operation when the 

 propulsion turbines and the main steam system 

 are secured. The steam is admitted to the turbine 

 through a throttle trip valve to the steam chest, 

 the speed being regulated by a number of nozzle 

 control valves under the control of a governor. 



Because the ship's service generator must 

 supply electricity at a constant voltage and fre- 

 quency, the turbine must run at a constant speed 

 even though the load varies greatly. Constant 

 speed is maintained through the use of a constant- 

 speed governor (discussed later in this chapter). 



As may be seen in figure 16-6, the shaft 

 glands of the ship's service generator turbine are 

 supplied with gland sealing steam. The system 

 is much the same as that provided for propulsion 

 turbines. Other auxiliary turbines in naval use 

 do not require an external source of gland seal- 

 ing steam since they exhaust to pressures above 

 atmospheric pressure. 



Generator turbines vary greatly, and are not 

 all like the one shown in figure 16-6. For 

 example, one recent type of turbogenerator con- 

 sists of seven stages— one Curtis stage and six 

 Rateau stages. This turbine is direct drive, 

 rather thangeared; the turbine operates at 12,000 

 rpm and so does the generator. 



AUXILIARY TURBINE LUBRICATION 



Auxiliary turbines designed to Navy specifi- 

 cations have pressure lubrication systems to 

 lubricate the radial bearings, reduction gears. 



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