A control valve is a valve used to control flow as directed by a signal. This enables the control of flow rate and the charge of process quantities like pressure, temperature, and liquid level. Electrical, hydraulic or pneumatic actuators usually perform the opening or closing of control valves. Normally with a modulating valve, which can be set to any position between fully closed and fully open, valve positioners are used to ensure the valve accomplishes the degree of opening. If you are searching for additional details on instrumentation, browse the mentioned above website.
Valves are used because of their simplicity, as they require a compressed air source, whereas electrically-operated valves need additional cabling and switchgear, and hydraulically-actuated valves needed high-pressure supply and return lines for the fluid. A variety of control operation and valve types exist. But, there are two forms of activity; the sliding stem and the rotary action. The most common and versatile kinds of control valves are angle types , V-notch ball, butterfly and a sliding-stem world. Their popularity derives from rugged construction as well as the many options available which make them suitable for a variety of process applications. It is used primarily for throttling purposes. It may be considered a general purpose flow control valve temp application. Quicker to open a reliable form of seating, or close, throttling to control the flow to any desired level, positive shut-off. The most common final control element in the process control industries is the control valve.
The control valve manipulates a fluid, such as gas, steam, water, or chemical compounds, to compensate for the load disturbance and keep the process variable as close as possible to the set point. Control valves might 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 such as mechanics, metallurgy, sound management, and vessel and piping design, terminologies, and the many 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 compares the “process variable” obtained 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 controller the brain the last control element is the hands of the control loop. This makes it the alas sometimes the least understood, part of an automatic control system. This comes about, in part, due to our strong attachment to computers and electronic systems causing some neglect in the proper understanding and proper use of the all-important hardware.