PRINCIPLES OF NAVAL ENGINEERING 



f 



CORRECTION 



— (CLOSED LOOP) 



COLD WATER INPUT 



STEAM INPUT 



STEAM 



VALVE 



(FINAL 



CONTROL 



ELEMENT) 



VALVE 



MOTOR 



OPERATOR - 



THE HEAT EXCHANGE 



PROCESS 



ACTUATING ■ 

 SIGNAL 



COMPARISON 



AND 

 COMPUTATION 



CAPILLARY 

 TUBING 



SET 

 POINT 

 KNOB- 



VANE- 

 NOZZLE- 



/— ~ -> ■ qtmnn i itim w 



PNEUMATIC 

 TRANSMITTER 



h' 



iHHWMIllcf 



BOURDON 

 TUBE 



SUPPLY AIR 



(CLOSED LOOP) 



98.101 



Figure 11-39.— Simple automatic control system for control 

 of heat exchange process. 



The remainder of this discussion deals with 

 Bailey boiler controls which have been installed 

 on several ships that have 1200-psi boilers. It 

 should be noted that boiler control systems in- 

 stalled in naval ships are by no means identical. 

 The systems made by different manufacturers 

 (including Bailey, General Regulator, and Hagan) 

 are different in many respects. Although the 

 systems made by any one manufacturer tend to 

 utilize the same kind of components, the layout 

 of the systems and the variables involved may 

 vary considerably. Hence the following discus- 

 sion of Bailey boiler controls should be regarded 

 as an example rather than as a standard. 



In Bailey boiler control systems, we must 

 distinguish three kinds of air pressure. Loading 



pressure is the term used to describe the pneu- 

 matic signal pressure between two pneumatic 

 units of the control system, except when the 

 pressure is imposed upon a control valve or a 

 control drive. Control pressure is the term used 

 to describe the pneumatic pressure going to the 

 diaphragm of a control valve or to the piston of 

 a control drive. For example, we would call 

 the pneumatic output of a steam pressure trans- 

 mitter loading pressure because it goes to a 

 pneumatic relay; if the pressure were imposed 

 directly upon a control drive or a control valve, 

 instead of upon the intervening relay, the pres- 

 sure would be called control pressure . Each 

 pneumatic unit in the system requires a supply 

 of compressed air so that it can develop the 



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