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How to choose valve positioner correctly

How do valve positioners and control valves form a loop?
The valve positioner is the main accessory of the control valve. It is used with the regulating valve to receive the output signal of the regulator, and then control the regulating valve with its output signal. After the regulating valve acts, the displacement of the valve stem is fed back to the valve positioner through the unloading device. Therefore, this kind of positioner and the regulating valve form a closed-loop loop loop.
How to classify valve positioners according to structure and working principle?
Valve positioners can be divided into pneumatic valve positioner, electro pneumatic valve positioner and intelligent valve positioner according to its structure and working principle.
What are the functions of valve positioners?
1. Improve the static characteristics of the control valve and improve the linearity of the valve position.
2. Improve the dynamic characteristics of the control valve and reduce the signal transmission lag of the control valve.
3. Change the flow characteristics of the control valve.
4. Change the response range of control valve to signal pressure to realize split range control.
4. Reverse the valve action.
Why can the valve positioner ensure the correct positioning of the control valve?
The valve positioner can increase the output power of the control valve, reduce the transmission lag of the regulating signal, speed up the moving speed of the valve stem, improve the linearity of the valve, overcome the friction of the valve stem and eliminate the influence of the unbalanced force, so as to ensure the correct positioning of the control valve.
Why should a meter be equipped with a locator under high pressure medium?
When the control valve is used in high-pressure medium, in order to prevent the fluid from leaking from the valve stem packing, the packing is often tightly capped. Therefore, a great friction force is generated in the valve stem, which is caused by the error of the stem stroke. After the positioner is used, it can overcome the effect of these friction forces and the effect of fluid imbalance force, which obviously improves the basic characteristics.
What is the function of positioner under high pressure difference?
When the pressure difference between the two ends of the control valve is greater than 1MPa, the medium will produce a large unbalanced force on the valve core, which will destroy the original working position and cause disturbance to the control system. Especially for the single seat control valve, its unbalanced force is greater than that of the double seat valve. The use of positioner can increase the output pressure, increase the output force of the actuator and overcome the unbalanced effect.

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