Basics of Valves

Basics of Valves A valve is a mechanical device specially designed to control the fluid flow and pressure within a system or process. Valves are designed for either liquid or gaseous application. A valve carries out any of the following functions. Stopping and starting of flow of the fluid. Throttling the amount of fluid flow Controlling the fluid flow direction Regulating the downstream system or process pressure Relieving the over pressure in the system Regulating the temperature of process fluid Controlling the mixing of fluids Since there is diversity of the types of systems, fluids, and environments in which valves are to operate, valves have many designs and types which satisfy one or more of the identified functions. By nature of their design, function, and application, valves comes in a wide variety of styles, sizes, and pressure classes. A multitude of valve types and designs safely accommodate a wide variety of valve applications.  These days range of valves extends from simple water cocks to control valves equipped with microprocessors, which provide single loop control of the process. The most common types of valves in use today are gate, globe, plug, ball, needle, butterfly, check, pressure relief, diaphragm, pinch, and safety valves etc. Valves are manufactured from a number of materials which include carbon steel, alloy steel, stainless steel, iron, brass, bronze, aluminum, plastics and a number of special alloys. Valves can have threaded end connection, flanged end connection, welded connection, or other type of connection like union end connections in case of some plastic valves. Regardless of type, all valves have the basic components which include valve body, bonnet, trim (internal elements), actuators, and packing. These are described below. A valve along with its basic components is shown in Fig 1. Fig 1 A...