PRINCIPLES OF NAVAL ENGINEERING 



STEAM 

 PRESSURE 



STEAM FLOW 



LOAD 

 DEMAND 

 RELAY 



AIR FLOW 



LIMITER 



AIR 

 FLOW 



FUEL 

 BURNED 



FUEL 1^ 

 FLOW 



STEAM 

 FLOW 



\ 



/ STEAM V 



(FLOW - FEE[? 



■^ WATER FLOWP" 



^UNBALANCE/ 



DRUM 

 WATER 

 LEVEL 



1 



FEED 



WATER 



FLOW 



Figure 11-40.— Control relationships, Bailey combustion control system and 



feed water control system. 



98. 108:. 109 



the minimum and the maximum points of the 

 range. 



The output signal from each of the steam 

 pressure transmitters is applied to the steam 

 pressure selective relay (Clb). The selective 

 relay selects and transmits the higher of the 

 two signals to the steam demand relay (C4al). 

 This relay is so adjusted that its output remains 

 constant when the steam pressure is constant at 

 1200 psig. 



While this is going on, steam flow from each 

 boiler is being measured by steam flow trans- 

 mitters (F2). The steam flow transmitters meas- 

 ure the pressure drop across a restriction in the 

 steam line and extract the square root of this 

 pressure drop. The output loading pressures 

 from the steam flow transmitters are propor- 

 tional to the square root of the pressure 

 drop— or, in other words, proportional to the 

 rate of flow. The output loading pressure of a 

 steam flow transmitter ranges from 3 psig to 

 27 psig as the steam flow ranges from minimum 



to maximum. The loading pressure from each 

 of the steam flow transmitters is applied to the 

 steam flow selective relay (F2b). The selective 

 relay then transmits the higher of the two load- 

 ing pressures to the steam demand relay 

 (C4al). 



The output steam demand signal from the 

 steam demand relay (C4al) passes through the 

 boiler master selector valve (C5a). The boiler 

 master selector valve has no effect on the signal 

 during automatic operation. After passing 

 through the boiler master selector valve, the 

 output loading pressure from the steam demand 

 relay is applied to the combustion air Standa- 

 trol (C4b) and to the fuel limiting relay (C15). 

 A measured combustion air flow signal is trans- 

 mitted from the air flow transmitter (C3) through 

 the excess air remote adjustable relay (C9), 

 where the signal can be manually adjusted for 

 excess air requirements for low-load steaming, 

 maneuvering, or soot blowing. The air flow 

 signal is then applied to the combustion air 

 Standatrol (C4b). 



314 



