By definition, a valve is a specially designed mechanical device for directing, starting, stopping, mixing, or regulating the flow, pressure, or temperature of a process fluid. Valves can be designed to handle the operation of liquids or gases. There are many types, types, and pressure ratings depending on the design, function, and application characteristics of the valve. Small industrial valves can weigh as little as 1 lb (0.45 kg) and are placed in the hands of people. The large one can be heavier than 10t (9070kg) and the height is above 24ft (601m). Industrial process valves can be used for line sizes from 0.5m [nominal diameter (DN15)] to over 48in (DN1200). However, more than 90% of the valves used on the process system are installed in 4in (DN100) or smaller sizes. Valve pressure can be used from negative pressure to over 1300 psi (897 bar). An example of how the process valve size changes is shown in Figure 1.1....

 

Today's existing valve showers have evolved from simple faucets to control valves equipped with information processors that provide single loop control of the process. Common types used today are gate valves, plug valves, ball valves, butterfly valves, check valves, pressure relief valves, and globe valves.

 

Valves can be made from a wide variety of materials, most of which are made of steel, iron, plastic, brass, bronze or a large number of special alloys.