Chapter 10- PROPULSION BOILERS 



As may be seen, classifying boilers by oper- 

 ating pressure is not very precise, since actual 

 operating pressures may vary widely within one 

 group. Also, any classification based on operat- 

 ing pressure may easily become obsolete. What 

 is called a high pressure boiler today might well 

 be called a low pressure boiler tomorrow. 



BOILER COMPONENTS 



Most propulsion boilers now used by the 

 Navy have essentially the same components: 

 steam and water drums, generating and circu- 

 lating tubes, superheaters, economizers, fuel 

 oil burners, furnaces, casings, supports, and a 

 number of accessories and fittings required for 

 boiler operation and control. The basic com- 

 ponents of boilers are described here. In later 

 sections of this chapter we will see how the 

 components are arranged to form various com- 

 mon types of naval propulsion boilers. 



Drums and Headers 



Drum-type boilers are installed in the ship 

 in such a way that the long axis of the boiler 

 drums will run fore and aft rather than athwart- 

 ships, so that the water will not surge from one 

 end of the drum to the other as the ship rolls. 



The steam drum is located at the top of the 

 boiler. It is cylindrical in shape, except that on 

 some boilers, it may be slightly flattened along 

 its lower curved surface. The steam drum re- 

 ceives feed water and serves as a place for the 

 accumulation of the saturated steam that is gen- 

 erated in the tubes. The tubes enter the steam 

 drum below the normal water level of the drum. 

 The steam and water mixture from the tubes 

 goes through separators which separate the 

 water from the steam. 



Figure 10-3 shows the way in which a steam 

 drum is constructed. Two sheets of steel are 

 rolled or bent to the required semicircular 

 shape and then welded together. The upper sheet 

 is called the wrapper sheet; the lower sheet is 

 called the tube sheet. Notice that the tube sheet 

 is thicker than the wrapper sheet. The extra 

 thickness is required in the tube sheet to ensure 

 adequate strength of the tube sheet after the 

 holes for the generating tubes have been drilled. 

 The ends of the drum are enclosed with drum- 

 heads which are welded to the shell, as shown in 

 figure 10-4. One drumhead contains a manhole 

 which permits access to the drum for inspec- 

 tion, cleaning, and repair. 



WRAPPER 

 SHEET 



TUBE SHEET 



38.19 



Figure 10-3.— Boiler steam drum. 



The steam drum either contains or is con- 

 nected to many of the important fittings and 

 instruments required for the operation and 

 control of the boiler. These fittings and controls 

 are discussed separately in chapter 11 of this 

 text. 



Water drums and water headers equalize the 

 distribution of water to the generating tubes and 

 provide a place for the accumulation of loose 

 scale and other solid matter that may be present 

 in the boiler water. In drum-type boilers, the 

 water drums and water headers are at the 



DRUMHEAD 



38.20 

 Figure 10-4.— Drumhead secured to steam drum 

 shell. 



235 



