A control valve is a valve used to control flow by varying the size of the flow passage as directed by a signal. This permits the direct control of flow rate and the consequential charge of process quantities such as pressure, temperature, and liquid level. Hydraulic or pneumatic actuators usually perform the opening or closing of automatic control valves. Normally using a modulating valve, which is set to any position between fully closed and fully open, valve positioners are used to ensure the valve attains the desired level of opening. Are you looking for temperature measurement? Visit the before mentioned site.
Valves are used because of their simplicity, since they only require a compressed air supply, whereas electrically-operated valves need cabling and switchgear, and hydraulically-actuated valves required high-pressure supply and return lines to the hydraulic fluid. A huge range of valve types and control operation exist. However, there are two chief kinds of action; the sliding stem and the rotary action. The most common and versatile types of control valves are angle types , V-notch ball, butterfly and a globe. Structure is derived from by their popularity and the many options available which make them suitable for a variety of process applications. It’s used primarily for throttling functions.
It may be thought of as a general purpose flow control valve high temp application. Quicker to open or close, a form of seats, throttling to control the flow to any degree that is desired. 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 may be the most important, but sometimes the most neglected, part of a control loop. The reason is usually the instrument engineer’s unfamiliarity with the facets, terminologies, and regions of engineering disciplines like mechanics, metallurgy, noise management, and piping and vessel design which 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 which contrasts the “process variable” received from the transmitter with the “set point,” i.e., the desirable 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 sensors of the process variables are the eyes, the control the brain the control element is the hands of the control loop. This makes it the most important, alas sometimes the least known, part of an automatic control system. This comes about, in part, due to our strong attachment to electronic systems and computers causing some neglect in the proper understanding and proper use of their hardware.