Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGSTEAMPRESSURESTEAM FLOWAIR FLOWFUELBURNEDLOADDEMANDRELAYLIMITERAIRFLOWFUELFLOW1^STEAMFLOWDRUMWATERLEVEL\/ STEAM V(FLOW - FEE[?^WATER FLOWP"^UNBALANCE/1FEEDWATERFLOWFigure 11-40.— Control relationships, Bailey combustion control system andfeed water control system.98. 108:. 109the minimum and the maximum points of therange.The output signal from each of the steampressure transmitters is applied to the steampressure selective relay (Clb). The selectiverelay selects and transmits the higher of thetwo signals to the steam demand relay (C4al).This relay is so adjusted that its output remainsconstant when the steam pressure is constant at1200 psig.While this is going on, steam flow from eachboiler is being measured by steam flow transmitters(F2). The steam flow transmitters measurethe pressure drop across a restriction in thesteam line and extract the square root of thispressure drop. The output loading pressuresfrom the steam flow transmitters are proportionalto the square root of the pressuredrop— or, in other words, proportional to therate of flow. The output loading pressure of asteam flow transmitter ranges from 3 psig to27 psig as the steam flow ranges from minimumto maximum. The loading pressure from eachof the steam flow transmitters is applied to thesteam flow selective relay (F2b). The selectiverelay then transmits the higher of the two loadingpressures to the steam demand relay(C4al).The output steam demand signal from thesteam demand relay (C4al) passes through theboiler master selector valve (C5a). The boilermaster selector valve has no effect on the signalduring automatic operation. After passingthrough the boiler master selector valve, theoutput loading pressure from the steam demandrelay is applied to the combustion air Standatrol(C4b) and to the fuel limiting relay (C15).A measured combustion air flow signal is transmittedfrom the air flow transmitter (C3) throughthe excess air remote adjustable relay (C9),where the signal can be manually adjusted forexcess air requirements for low-load steaming,maneuvering, or soot blowing. The air flowsignal is then applied to the combustion airStandatrol (C4b).314