PRINCIPLES OF NAVAL ENGINEERING 



ASTERN STEAM INLET 



AHEAD STEAM FROM 

 H.P. TURBINE 



ASTERN STEAM INLET 



ASTERN 

 NOZZLE 

 BLOCK 



47,8X 



Figure 12-14.— Double-flow reaction turbine. 



separated only by a fluid film of oil. The 

 effectiveness of oil-film lubrication depends 

 upon a number of factors, including properties 

 of the lubricant (cohesion, adhesion, viscosity, 

 temperature, etc.) and the clearances, align- 

 ment, and surface condition of the bearing and 

 the journal. Except for the momentary metal- 

 to-metal contact when the turbine is started, 

 the metallic surfaces of the bearing and the 

 journal are constantly separated by a thin film 

 of oil. 5 



As previously noted, impulse turbines do not, 

 in theory, develop end thrust. In reality, how- 

 ever, a small amount of end thrust is developed 

 which must be absorbed in some way. Kingsbury 

 or pivoted-shoe thrust bearings are usually used 

 on propulsion turbines. 



Shaft Glands 



Shaft glands are used to minimize steam 

 leakage from the turbine casing (or air leakage 

 into the casing) at the points where the shaft 

 extends through the casing. Two types of packing, 

 carbon packing and labyrinth packing, are used 

 in shaft glands. 



Lubricants and the oil-film theory of lubrication are 

 discussed in chapter 6 of this text. 



Carbon packing is suitable only for relatively 

 low pressures and temperatures. When both 

 types of packing are used in one gland, there- 

 fore, as shown in figure 12-20, the labyrinth 

 packing is used at the initial high pressure 

 area and the carbon packing is used at the 

 lower pressure area. Since most modem ships 

 utilize relatively high pressures and tempera- 

 tures, most modern propulsion turbines are 

 only labyrinth packing. 



Labyrinth packing consists of rows of me- 

 tallic strips or fins. These strips are fastened 

 to the gland liner in such a way as to make a 

 very small clearance between the strips and the 

 shaft. As the steam from the turbine leaks 

 through the small spaces between the packing 

 strips and the shaft, the steam pressure is 

 gradually reduced. 



Where carbon packing rings are used, they 

 restrict the passage of steam along the shaft 

 in much the same manner as do the laby- 

 rinth packing strips. Carbon packing rings are 

 mounted around the shaft and are held in place 

 by springs. As a rule, three or four carbon 

 rings are used in each gland; each ring is 

 fitted into a separate compartment of the gland 

 housing. 



Gland Sealing Systems 



On propulsion turbines, the shaft gland 

 packing is not sufficient to entirely stop the 



330 



