Chapter 11-BOILER FITTINGS AND CONTROLS 



HAND LIFTING LEVER* 



SPINDLE 1 



SPINDLE LOCK CLIP 



ADJUSTING RING 

 SET SCR EW 



ADJUSTING RING 



DISK INSERT 



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Figure 11-19.— Steam drum safety valve (nozzle reaction type). 



connected by piping to the space above the disk 

 in the superheater actuated (or unloading) valve. 

 The unloading valve has no spring and relies 

 solely on pressure differential for its operation. 

 Normally there is a static pressure above the 

 disk of the unloading valve, since a small orifice 

 (or in some designs a small clearance around 

 the disk) allows some steam at superheater out- 

 let pressure to enter the space above the disk. 



When the drum valve is opened by steam 

 drum pressure, the mechanical connection be- 

 tween the drum valve and the actuating valve 

 causes the actuating valve to open also. With 

 the actuating valve open, steam flows from the 

 space above the disk of the superheater un- 

 loading valve, through the actuating line, through 

 the actuating valve, to atmosphere. The sudden 

 relief of pressure above the disk of the unloading 



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