Principles of naval engineering - Historic Naval Ships Association

.IIChapter 12- PROPULSION STEAM TURBINESASTERN STUMWinASTWM »K*DBUOE ttACTWHGROUPBUWMSTEAM INLET\ FROM H.P. TUIMNEASTERN STEAM INLHASTERN NOZZlf BLOCKASTERNN0Z21IBLOCKCARBONPACKING oGIANO6UND STEAMS£AL^^ASTERN BUDE GROUPROTOR POSITIONMICROMETEREMERGENCYOIL\f7lG0VERN0RBEARINGINLETOILBEARING&GOVERNORPUMPOIL. INLETBEARINGOIL DRAINEXHAUSTFLANGETO CONDENSERBLADE EXHAUST STEAM DRAIN EXHAUST STEAMSHIELD DEFLECTOR OEFIICTORBUDE BAFFLE GLANO \SHKLD CENTERING PM DRAINBEARING OILDRAINFigure 12-27.— Low pressure turbine(with astern elements).147,101or CPO in charge of an engineroom watch, cancontribute a great deal to the economical andsafe operation of the boilers if they use theacceleration and deceleration charts providedfor that particular propulsion plant.Acceleration and deceleration charts areposted at each main engine throttle board. Thesecharts give the exact amount of time that thethrottleman should use in changing speed. Whena speed change is ordered, the throttleman cantell instantly, by checking the chart, the minutesand seconds necessary for him to accelerateor decelerate to the new speed. Main enginecontrol has tachometers indicating the numberof rpm each shaft is doing. By means of thetachometers, the engineeringofficer of the watchcan coordinate the rpm of the shafts; if onethrottleman accelerates or decelerates toorapidly or too slowly, the engineering officerof the watch can detect the trouble and haveit corrected.Improper acceleration or decelerationwastes fuel, leads to uneconomical operation ofthe propulsion plant, and may cause operationalproblems in the fire room. Each throttlemanshould have a revolution - pressure table whichgives the approximate pressure required in thefirst stage of the high pressure turbine to developa certain rpm. By using such a table,together with the acceleration and decelerationcharts, the throttleman can make his watchstandingmuch easier and, at the same time,contribute to economical and efficient operationof the plant. There must always be completeunderstanding between the engineroom and thebridge as to how many rpm are to be maintainedfor one-third, two-thirds, standard, and fullspeed. The throttleman should never relievethe watch without knowing the rpm for thesespeeds.For most efficient turbine operation, thehighest possible vacuum must be maintainedin the condenser. Air must not be allowed toleak into the condenser, exhaust trunks, throttles,lines to air ejectors, gage lines, idlecondensate pump packing, makeup feed lines,or any other part of the system under vacuum.A steam pressure of 1/2 to 2 psi must be341