A control valve is a valve used to control fluid flow by changing the size of the flow passage as directed by a signal. This enables the control of flow rate and the charge of process quantities like pressure, temperature, and liquid level. Hydraulic or pneumatic actuators usually perform the opening or closing of automatic control valves. With a modulating valve, which is 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 looking for more information on temperature measurement, check out the above website.
Air-actuated valves are commonly used because of their simplicity, as they only require a compressed air source, whereas electrically-operated valves need cabling and switchgear, and valves needed high-pressure supply and return lines to the fluid. A variety of control operation and valve types exist. However, there are two forms of activity; the rotary action and the stem. The versatile and most common kinds of control valves are V-notch ball, a globe, butterfly and angle types. Rugged construction is derived from by their popularity and the many options available that make them suitable for many different process applications.
It’s used primarily for throttling purposes. It may be thought of as a general purpose flow control valve temp program. Quicker to open a most reliable form of seats, or close, throttling to control the flow to any level. The most common control element from 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 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 the aspects, terminologies, and regions of engineering disciplines like mechanics, metallurgy, sound control, 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 compares 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 sensors of the process variables are the eyes, the control the mind the last control element is the hands of the control loop. This makes it the alas sometimes the least known, part of an automatic control system. This comes about due to our strong attachment to computers and electronic systems causing some fail in the proper understanding and proper use of the hardware.