VALVE FUNCTIONS AND BASIC PARTSDOE-HDBK-1018/2-93ValvesValveBodyThe body,sometimes called the shell, is the primary pressure boundary of a valve. It serves asthe principal element of a valve assembly because it is the framework that holds everythingtogether.The body, the first pressure boundary of a valve, resists fluid pressure loads from connectingpiping. It receives inlet and outlet piping through threaded, bolted, or welded joints.Valve bodies are cast or forged into aFigure 1 Basic Parts of a Valvevariety of shapes. Although a sphereor a cylinder would theoretically bethe most economical shape to resistfluid pressure when a valve is open,there are many other considerations.For example, many valves require apartition across the valve body tosupport the seat opening, which is thethrottling orifice. With the valveclosed, loading on the body isdifficult to determine. The valve endconnections also distort loads on asimple sphere and more complicatedshapes. Ease of manufacture,assembly, and costs are additionalimportant considerations. Hence, thebasic form of a valve body typicallyis not spherical, but ranges fromsimple block shapes to highlycomplex shapes in which the bonnet,a removable piece to make assemblypossible, forms part of the pressure-resisting body.Narrowing of the fluid passage(venturi effect) is also a commonmethod for reducing the overall sizeand cost of a valve. In otherinstances, large ends are added to thevalve for connection into a largerline.ME-04Rev. 0Page 2
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