Publisher Summary Control valves can be grouped into two major classifications: process and fluid power. Process valves control the flow of gases and liquids through a process system. Fluid-power valves control pneumatic or hydraulic systems. Process-control valves are available in a variety of sizes, configurations, and materials of construction. Generally, this type of valve is classified by its internal configuration. The device used to control flow through a valve varies with its intended function. The more common types are ball, gate, butterfly, and globe valves. Operating methods for control valves, which are designed to control or direct gas and liquid flow through process systems or fluid-power circuits, range from manual to remote, automatic operation. The key parameters that govern the operation of valves are the speed of the control movement and the impact of speed on the system. Further, fluid power control valves are used on pneumatic and hydraulic systems or circuits. The configuration of fluid power control valves varies with their intended application. The more common configurations include one-way, two-way, three-way, and four-way. The function and proper operation of a fluid-power valve are relatively simple. Most of these valves have a schematic diagram affixed to the body that clearly explains how to operate the valve.