Chapter 14. -PIPING, FITTINGS, AND VALVES 



LOCK NUT 



ADJUSTING SCREW 



ADJUSTING SPRING 



CONTROLLING DIAPHRAGM 



PISTON STEAM PORT 



PISTON 



HIGH PRESSURE- 

 PORT 



AUXILIARY VALVE 



AUXILIARY VALVE 

 SPRING 



■ LOW PRESSURE 

 PORT 



MAIN VALVE SPRING- 



-MAIN VALVE 



DRAIN CONNECTION 



47.59X 



Figure 14-20.— Spring-loaded reducing valve. 



by the reduced pressure steam. These two forces 

 are continually seeking to reach a state of bal- 

 ance; and, because of this, the discharge pres- 

 sure of the steam is kept constant as long as the 

 amount of steam used is kept within the capacity 

 of the valve. 



There are two types of gas-loaded (or pneu- 

 matic pressure controlled) reducing valves. One 

 type, shown in figure 14-21, is designed to regu- 

 late pressure in low temperature air, water, oil, 

 or other fluids. The other type, shown in figure 

 14-22, is designed to regulate pressure in high 

 temperature steam, hot water, or other fluids. 

 Both types of valves operate on the principle that 

 the pressure of an enclosed gas varies inversely 

 as its volume. 



We will consider first the valve for low tem- 

 perature service (fig. 14-21). In this valve, a 



relatively small change in the large volume with- 

 in the dome loading chamber produces only a 

 slight pressure variation, while the slightest 

 variation in the small volume within the actuat- 

 ing chamber creates an enormous change in 

 pressure. The restricting orifice connecting 

 these two chambers governs the rate of pressure 

 equalization by retarding the flow of gas from one 

 chamber to another. 



The dome loading chamber is charged with air 

 or some other compressible gas at a pressure 

 equal to the desired reduced pressure. When the 

 chamber is loaded, and the loading valve is 

 closed, the dome will retain its charge almost 

 indefinitely. When the regulator is in operation, 

 the trapped pressure within the dome passes into 

 the actuating chamber through the small separa- 

 tion plate orifice and moves the large flexible 



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