PRINCIPLES OF NAVAL ENGINEERING 



VENT OR 

 FILLING LINES 



CALIBRATION 



ADJUSTING 



SCREW 



ZERO 



ADJUSTING 



SCREW 



POINTER 

 HUB 



SEALING 

 PLUG 



DEFLECTION 

 PLATE 



DIAPHRAGM 



MAGNET 



PRESSURE FROM 



SUPERHEATER 



OUTLET 



PRESSURE FROM 



SUPERHEATER 



INLET 



98.91 



Figure 11-30.— Cross section of Yarway indicating unit (front view). 



the capillary tube, and the spiral-shaped Bour- 

 don element are filled with mercury. As the 

 temperature rises, the mercury expands and 

 causes the Bourdon tube to move so that an 

 attached cantilever arm is moved toward an 

 electric microswitch. When the temperature 

 reaches a predetermined point, the cantilever 

 arm closes the microswitch, actuating a warn- 

 ing light and a warning howler. 



Smoke Indicators 



Naval boilers are fitted with smoke indi- 

 cators (sometimes called smoke periscopes) 

 which permit visual observation of the gases 

 of combustion as they pass through the up- 

 takes. Most single-furnace boilers have one 

 smoke indicator installed in the uptake. Double- 

 furnace boilers have two smoke indicators, 



one for observing the combustion gases coming 

 from the saturated side and the other for ob- 

 serving the combustion gases coming from the 

 superheater side. 



A smoke indicator is shown in figure 11-36. 

 A light bulb is installed in a lamp unit at the 

 rear of the boiler. At the front of the boiler, 

 in direct line of sight with the lamp, is a re- 

 flector unit which reflects the image to a 

 second mirror. The second mirror is located 

 so that it may be seen from the fireroom. 



Oil Drip Detector Periscopes 



Some boilers are equipped with oil drip 

 detector periscopes which permit inspection 

 of the floor between the inner and outer boiler 

 castings, to see if oil has accumulated there. 



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