By definition, a valve is a specially designed mechanical device to flow, start, stop, mix or regulate the flow, pressure or temperature of a process fluid. Valves can be designed to handle liquid or gas operations. Valves come in many types, sizes and pressure ratings according to their design, function and application characteristics. Small industrial valves can weigh as little as 1 lb (0.45kg) and fit in a human hand. And the big one can weigh more than 10t (9070kg) and the height can reach more than 24ft (601m). Industrial process valves can be used for pipeline sizes from 0.5m [nominal diameter (DN15)] to over 48in (DN1200). However, more than 90% of the valves used in the process system are installed on 4in (DN100) or smaller pipelines. Valve pressure can be used from negative pressure to over 1300 psi (897 bar). An example of how process valve size changes are shown in Figure 1.1. …
Today’s existing valve showers have evolved from simple taps to control valves equipped with a processor that provides single loop control of the process. The types commonly used today are gate, plug, ball, butterfly, check, relief, and globe valves
Valves can be made from many kinds of materials, most valves are made of steel, iron, plastic, brass, bronze or a number of special alloys.