CHAPTER 11 



BOILER FITTINGS AND CONTROLS 



The fittings, instruments, and controls used 

 on naval boilers are sufficiently numerous and 

 important to warrant separate discussion. The 

 term boiler fittings is used to describe a num- 

 ber of attachments which are installed in or 

 closely connected to the boiler and which are 

 required for the operation of the boiler. Boiler 

 fittings are generally divided into two classes. 

 Internal fittings (also called internals ) are those 

 installed inside the steam and water spaces of 

 the boiler; external fittings are those installed 

 outside the steam and water spaces. Boiler 

 instruments such as pressure gages and tem- 

 perature gages are usually regarded as external 

 bqiler fittings. Boiler controls are special sys- 

 tems which automatically control the fuel oil, 

 combustion air, and feed water inputs in order 

 to regulate the steam output of the boiler. 



ESTTERNAL FITTINGS 



The internal fittings installed in the steam 

 drum usually include equipment for distributing 

 the incoming feed water, for giving surface 

 blows, and for directing the flow of steam and 

 water within the steam drum. In addition, boilers 

 which do not have controlled superheat have 

 desuperheaters for desuperheating steam needed 

 for auxiliary purposes; the desuperheater is 

 most commonly installed in the steam drum, 

 but is installed in the water drum in some of 

 the newer boilers. Internal fittings in some 

 boilers also include equipment for injecting 

 chemicals for boiler water treatment. 



The specific design and arrangement of 

 boiler internal fittings varies somewhat from 

 one type of boiler (and from one boiler manu- 

 facturer) to another. The arrangement of inter- 

 nals in several boilers is therefore described 

 here. 



Figure 11-1 illustrates atypical arrangement 

 of internal fittings installed in the steam drum 



of a header-type boiler. This illustration also 

 shows many of the external connections. Feed 

 water enters through the feed inlet (A) and flows 

 to the internal feed pipe (B), The feed pipe is 

 capped at one end. The horizontal part of the 

 feed pipe runs about 80 percent of the length of 

 the drum, well below the normal water level. 

 The feed pipe is perforated along the upper side 

 so that the feed water will be evenly distributed 

 along the length of the pipe. 



The dry pipe (C) is suspended near the top 

 of the steam drum, along the centerline of the 

 drum. Both ends of the dry pipe are closed. 

 Steam enters by way of perforations in the 

 upper surface of the dry pipe. Thus the steam 

 must change direction in order to enter the dry 

 pipe. Since some moisture is lost whenever 

 steam changes direction, the dry pipe acts as 

 a device to separate steam and moisture. Steam 

 leaves the dry pipe through the main steam out- 

 let (D) and from there goes to the superheater. 

 A few perforations in the bottom of the dry pipe 

 allow water droplets to drain back down to the 

 water in the steam drum. 



A longitudinal baffle (N) also helps to sepa- 

 rate moisture from the steam before the steam 

 enters the dry pipe. The baffle is installed in 

 such a way as to allow steam to flow to the dry 

 pipe but to keep moisture (and any solid matter 

 that might be carried over with the moisture) 

 from entering the dry pipe. 



The surface blow-off pipe (E) is used to re- 

 move grease, scum, and light solids from the 

 boiler water and to reduce the salinity of the 

 boiler water while the boiler is steaming. The 

 surface blow-off pipe is installed near the cen- 

 ter of the steam drum, with the upper surface 

 of the pipe slightly below the normal water level 

 of the drum. The pipe runs almost the entire 

 length of the drum. Holes are drilled along the 

 top centerline of the pipe. One end of the pipe 

 is blanked off. The other end is connected through 



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