Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGthe supply pressure is at least as high as the desireddelivery pressure) and regardless of theamount of reduced pressure fluid that is used.There are several kinds of spring-loadedreducing valves. The one shown in figure 14-20is used for steam service, but is very similarto spring-loaded reducing valves used for otherservices.The principal parts of the valve are (1) themain valve, an upward-seating valve which hasa piston on top of its valve stem; (2) an upwardseatingauxiliary (or controlling) valve; (3) acontrolling diaphragm; and (4) an adjustingspring.High pressure steam (or other fluid) entersthe valve on the inlet side and acts against themain valve disk, tending to close the main valve.However, high pressure steam is also led throughports to the auxiliary valve, which controls theadmission of high pressure steam to the top ofthe main valve piston. The piston has a largersurface area than the main valve disk; therefore,a relatively smallamount of high pressure steamacting on the top of the main valve piston willtend to open the main valve, and so allow steamat reduced pressure to flow out the dischargeside.But what makes the auxiliary valve open toallow high pressure steam to get to the top ofthe main valve piston? The controlling diaphragmtransmits a pressure downward upon the auxiliaryvalve stem, and thus tends to open the valve.However, reduced pressure steam is led backto the chamber beneath the diaphragm; this steamexerts a pressure upward on the diaphragm,which tends to close the auxiliary valve. Theposition of the auxiliary valve, therefore, is determinedby the position of the controlling diaphragm.The position of the diaphragm at any given momentis determined by the relative strength of twoopposing forces: (1) the downward force exertedby the adjusting spring, and (2) the upwardforce exerted on the underside of the diaphragmLIST OF PARTS |valves, sizes iand smaller may be[furnished with convexIIwELDING ENDS