PRINCIPLES OF NAVAL ENGINEERING 



the supply pressure is at least as high as the de- 

 sired delivery pressure) and regardless of the 

 amount of reduced pressure fluid that is used. 



There are several kinds of spring-loaded 

 reducing valves. The one shown in figure 14-20 

 is used for steam service, but is very similar 

 to spring-loaded reducing valves used for other 

 services. 



The principal parts of the valve are (1) the 

 main valve, an upward-seating valve which has 

 a piston on top of its valve stem; (2) an upward- 

 seating auxiliary (or controlling) valve; (3) a 

 controlling diaphragm; and (4) an adjusting 

 spring. 



High pressure steam (or other fluid) enters 

 the valve on the inlet side and acts against the 

 main valve disk, tending to close the main valve. 

 However, high pressure steam is also led through 

 ports to the auxiliary valve, which controls the 

 admission of high pressure steam to the top of 

 the main valve piston. The piston has a larger 

 surface area than the main valve disk; therefore, 



a relatively smallamount of high pressure steam 

 acting on the top of the main valve piston will 

 tend to open the main valve, and so allow steam 

 at reduced pressure to flow out the discharge 

 side. 



But what makes the auxiliary valve open to 

 allow high pressure steam to get to the top of 

 the main valve piston? The controlling diaphragm 

 transmits a pressure downward upon the auxil- 

 iary valve stem, and thus tends to open the valve. 

 However, reduced pressure steam is led back 

 to the chamber beneath the diaphragm; this steam 

 exerts a pressure upward on the diaphragm, 

 which tends to close the auxiliary valve. The 

 position of the auxiliary valve, therefore, is de- 

 termined by the position of the controlling dia- 

 phragm. 



The position of the diaphragm at any given mo- 

 ment is determined by the relative strength of two 

 opposing forces: (1) the downward force exerted 

 by the adjusting spring, and (2) the upward 

 force exerted on the underside of the diaphragm 



valves, sizes i 

 and smaller may be 

 [furnished with convexI 



IwELDING ENDS 



Figure 14-19.— Stop-check valves. 

 378 



11.321 



