PRINCIPLES OF NAVAL ENGINEERING 



pump discharge pressure. When the booster 

 pump discharge pressure is inadequate, the aux- 

 iliary pilot valve will not deliver steam to the 

 controlling valve of the governor. Thus inade- 

 quate feed booster pump pressure allows the main 

 valve in the governor to close, shutting off the 

 flow of steam to the main feed pump turbine. 



SAFETY DEVICES 



Safety devices used on auxiliary turbines in- 

 clude speed-limiting governors and several 

 kinds of trips. Safety devices differ from speed 

 control devices in that they have no control over 

 the turbine under normal operating conditions. It 

 is only when some abnormal condition occurs that 

 the safety devices come into use to stop the unit 

 or to control its speed. 



Speed- Limiting Governors 



The speed-limiting governor is essentially 

 a safety device for variable speed units. It 

 allows the turbine to operate under all conditions 

 from no-load to overload, up to the speed for 



which the governor is set, but it does not allow 

 operation in excessof 107 percent of rated speed. 

 It is important to note that this type of governor 

 is adjusted to the maximum operating speed of 

 the turbine and therefore has no control over the 

 admission of steam until the upper limit of safe 

 operating speed is reached. 



One common type of speed- limiting governor 

 is shown in figure 16-12. This governor is used 

 on main condensate pumps, feed booster pumps, 

 lube oil service pumps, and other auxiliaries in 

 the engineering plant. The particular speed-lim- 

 iting governor shown here is designed for use on 

 a main condensate pump with a vertical shaft; 

 speed-limiting governors that operate on very 

 much the same principle are used on main feed 

 pumps and other auxiliaries that have horizontal 

 shafts. 



The governor shaft is driven directly by an 

 auxiliary shaft in the reduction gear, and rotates 

 at the same speed as the pump shaft. This speed 

 is proportional to— although lower than— the 

 speed of the driving turbine. Two flyweights are 

 pivoted to a yoke on the governor shaft and carry 



WEIGHTS 



Figure 16-12. — Speed-limiting governor. 

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