A control valve is a valve used to control flow by varying the size of the flow passage as guided by a signal from a controller. This permits the direct control of flow rate and the consequential charge of process quantities like pressure, temperature, and liquid level. Electrical, hydraulic or pneumatic actuators usually perform closing or the opening of automatic control valves. Using a modulating valve, which is set to any position between fully open and fully closed, valve positioners are used to ensure the valve attains the degree of opening. If you are searching to learn more about level measurement, go to the above website.
Air-actuated valves are generally used because of their simplicity, since they only require a compressed air source, whereas valves need cabling and switchgear, and hydraulically-actuated valves required high-pressure supply and return lines for the hydraulic fluid. A huge variety of control operation and valve types exist. However, there are two chief forms of activity; the action and the stem. The most common and versatile kinds of control valves are a sliding-stem worldball, butterfly and angle types. Their popularity the many options available as well as derives from structure which make them appropriate for many different process applications. It’s used primarily for throttling functions.
It may be thought of as a general purpose flow control valve high temp application. Faster to open a form of seats, or close, throttling to control the flow to any level. The most common control element in the process control industries is the control valve. The control valve manipulates a flowing fluid, such as steam, gas, water, or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the set point. Control valves may be the most important, but sometimes the most neglected, part of a control loop. The main reason is usually the instrument engineer’s unfamiliarity with areas of engineering disciplines like fluid mechanics, metallurgy, sound control, and vessel and piping design, terminologies, and the aspects that could be involved depending on the severity of service conditions.
Any control loop usually consists of a sensor of the process condition, a transmitter and a controller that contrasts the “process variable” received from the transmitter with the “set point,” i.e., the desired process condition. The controller, in turn, sends a corrective signal to the “final control element,” the final part of the loop and the “muscle” of the process control system. While the detectors of the process variables are the eyes, the control the mind, then the control element is the hands of the control loop. This makes it the alas sometimes the least understood, part of an automated control system. This comes about, in part, due to our strong attachment to computers and digital systems causing some fail in the proper understanding and proper use of their hardware.