Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGVENT ORFILLING LINESCALIBRATIONADJUSTINGSCREWZEROADJUSTINGSCREWDEFLECTIONPLATEDIAPHRAGMPOINTERHUBSEALINGPLUGMAGNETPRESSURE FROMSUPERHEATEROUTLETPRESSURE FROMSUPERHEATERINLETFigure 11-30.— Cross section of Yarway indicating unit (front view).the capillary tube, and the spiral-shaped Bourdonelement are filled with mercury. As thetemperature rises, the mercury expands andcauses the Bourdon tube to move so that anattached cantilever arm is moved toward anelectric microswitch. When the temperaturereaches a predetermined point, the cantileverarm closes the microswitch, actuating a warninglight and a warning howler.Smoke IndicatorsNaval boilers are fitted with smoke indicators(sometimes called smoke periscopes)which permit visual observation of the gasesof combustion as they pass through the uptakes.Most single-furnace boilers have onesmoke indicator installed in the uptake. Doublefurnaceboilers have two smoke indicators,30498.91one for observing the combustion gases comingfrom the saturated side and the other for observingthe combustion gases coming from thesuperheater side.A smoke indicator is shown in figure 11-36.A light bulb is installed in a lamp unit at therear of the boiler. At the front of the boiler,in direct line of sight with the lamp, is a reflectorunit which reflects the image to asecond mirror. The second mirror is locatedso that it may be seen from the fireroom.Oil Drip Detector PeriscopesSome boilers are equipped with oil dripdetector periscopes which permit inspectionof the floor between the inner and outer boilercastings, to see if oil has accumulated there.