12/23/2023 0 Comments Valve stemIn some designs, the body is machined to serve as the seating surface and seal rings are not used. The seat or seal rings provide the seating surface for the disk. Most valves are named, in part, according to the design of their disks. A fine surface finish of the seating area of a disk is necessary for good sealing when the valve is closed. Disks are typically forged and, in some designs, hard-surfaced to provide good wear characteristics. For this reason, the disk is a pressure-retaining part. With the disk closed, full system pressure is applied across the disk if the outlet side is depressurized. The disk provides the capability for permitting and prohibiting fluid flow. In linear motion trim designs, the disk lifts perpendicularly away from the seat so that an annular orifice appears.įor a valve having a bonnet, the disk is the third primary principal pressure boundary. In rotational motion trim designs, the disk slides closely past the seat to produce a change in flow opening. A valve's performance is determined by the disk and seat interface and the relation of the disk position to the seat.īecause of the trim, basic motions and flow control are possible. The trim typically includes a disk, seat, stem, and sleeves needed to guide the stem. The internal elements of a valve are collectively referred to as a valve's trim. Bonnets can complicate the manufacture of valves, increase valve size, represent a significant cost portion of valve cost, and are a source for potential leakage. Valve bonnets, although a necessity for most valves, represent a cause for concern. ![]() This means that the weld joint or bolts that connect the bonnet to the body are pressure-retaining parts. In all cases, the attachment of the bonnet to the body is considered a pressure boundary. It is cast or forged of the same material as the body and is connected to the body by a threaded, bolted, or welded joint. The bonnet is the second principal pressure boundary of a valve. Some bonnets function simply as valve covers, while others support valve internals and accessories such as the stem, disk, and actuator. Like valve bodies, bonnets vary in design. ![]() In some designs, the body itself is split into two sections that bolt together. The cover for the opening in the valve body is the bonnet. In other instances, large ends are added to the valve for connection into a larger line.įigure 1: Basic Parts of a Valve Valve Bonnet Narrowing of the fluid passage (venturi effect) is also a common method for reducing the overall size and cost of a valve. Hence, the basic form of a valve body typically is not spherical, but ranges from simple block shapes to highly complex shapes in which the bonnet, a removable piece to make assembly possible, forms part of the pressure-resisting body. Ease of manufacture, assembly, and costs are additional important considerations. The valve end connections also distort loads on a simple sphere and more complicated shapes. With the valve closed, loading on the body is difficult to determine. For example, many valves require a partition across the valve body to support the seat opening, which is the throttling orifice. Although a sphere or a cylinder would theoretically be the most economical shape to resist fluid pressure when a valve is open, there are many other considerations. Valve bodies are cast or forged into a variety of shapes. It receives inlet and outlet piping through threaded, bolted, or welded joints. The body, the first pressure boundary of a valve, resists fluid pressure loads from connecting piping. It serves as the principal element of a valve assembly because it is the framework that holds everything together. The body, sometimes called the shell, is the primary pressure boundary of a valve. The basic parts of a valve are illustrated in Figure 1. ![]() Regardless of type, all valves have the following basic parts: the body, bonnet, trim (internal elements), actuator, and packing. A multitude of valve types and designs safely accommodate a wide variety of industrial applications. There are many valve designs and types that satisfy one or more of the functions identified above. Relieving component or piping over pressure Regulating downstream system or process pressure Varying (throttling) the amount of fluid flow A valve controls system or process fluid flow and pressure by performing any of the following functions: This chapter will review the common parts and functions of a valve.Ī valve is a mechanical device that controls the flow of fluid and pressure within a system or process. Although there are many types, shapes, and sizes of valves, they all have the same basic parts. Valves are the most common single piece of equipment found in DOE facilities.
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