PRINCIPLES OF NAVAL ENGINEERING 



TO 

 ATMOSPHERE 



DRUM 



VALVE 



ACTUATING 

 VALVE 



SUPERHEATER 



UNLOADING 



(ACTUATED) 



VALVE 



I 



98.81 



Figure 11-20.— Pressure pilot-operated superheater outlet safety valve assembly. 



valve causes that valve to open fully, so that 

 steam is discharged from the unloading valve 

 to atmosphere. 



Many 1200-psi single-furnace boilers, and 

 also some 600-psi single-furnace ones, are 

 equipped with Crosby two-valve superheater 

 outlet safety valve assemblies of the type shown 

 in figure 11-21. In an assembly of this type, 

 both of the valves are spring loaded. The 

 pilot valve on the steam drum and the super- 

 heater valve at the superheater outlet are 

 connected by a pressure transmitting line that 

 runs from the discharge side of the drum pilot 

 valve to the underside of the piston that is 



attached to the spindle of the superheater safety 

 valve. The superheater valve is set to pop at a 

 pressure about 2 percent higher than the pres- 

 sure which causes the drum pilot valve to pop. 

 When the drum pilot valve pops, the steam pres- 

 sure is transmitted immediately through the 

 pressure line to the piston, and the superheater 

 valve is thus actuated. If for any reason the 

 drum pilot valve should fail to open, the super- 

 heater valve would open at a slightly higher 

 pressure. 



The Consolidated three-valve superheater 

 outlet safety valve assembly shown in figure 

 11-22 is used on a number of 1200-psi 



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