The valve positioner is the main accessory of the control valve. According to the structure, it can be divided into pneumatic valve positioner, electro-pneumatic valve positioner and intelligent valve positioner. It is usually used with pneumatic control valves. It receives the output signal of the regulator, and then uses the output signal to control the pneumatic control valve. When the control valve operates, the displacement of the valve stem is fed back to the valve positioner through the mechanical device, and the valve position status is transmitted to the upper system through the electrical signal.
Valve positioners can be divided into pneumatic valve positioners, electro-pneumatic valve positioners and intelligent valve positioners according to their structure and working principle.
The valve positioner can increase the output power of the regulating valve, reduce the transmission delay of the regulating signal, speed up the movement speed of the valve stem, improve the linearity of the valve, overcome the friction of the valve stem, and eliminate the influence of unbalanced force, so as to ensure the control valve correct positioning.
According to the input signal, the valve positioner is divided into pneumatic valve positioner, electric valve positioner and intelligent valve positioner. The input signal of the pneumatic valve positioner is a standard gas signal, such as a 20~100KPA gas signal, and its output signal is also a standard gas signal. The input signal of the electric valve positioner is a standard current or voltage signal, such as a 4~20mA current signal or a 1~5V voltage signal. In the electric valve positioner, the electric signal is converted into electromagnetic force, and then the air signal is output to the elbow control valve. The intelligent electric valve positioner converts the current signal from the control room into a gas signal to drive the control valve. According to the friction of the valve stem when the control valve is working, the unbalanced force caused by the fluctuation of the medium pressure is offset, so that the valve opening corresponds to the current signal of the control room, and the corresponding parameters can be intelligently set to improve the performance of the control valve.
