Troubleshooting of valve positioner output pressure shock Common valve positioner classification and principle
Check the output pressure oscillation of valve positioner
With the popularization of industrial automation, as the regulator valve control unit locator also highlights the important role. Positioner is a device that receives electrical signals from the control system and converts them into gas signals to control valve position. The control accuracy of a regulating valve, excluding the design factors of the valve body, completely depends on the regulating accuracy of the positioner. Then we often encounter the phenomenon of the output pressure oscillation of the locator in the process of using the locator. The troubleshooting method is as follows:
1, first of all, the valve and positioner connection parts are excluded whether loose, installation position is correct.
2. If it is a mechanical positioner, attention should also be paid to whether the pressure reducing valve matches the positioner.
3, see whether there is a high power electrical equipment around, eliminate electromagnetic interference.
4. Eliminate the leakage of the connecting pipe of each air source.
5. If it is a single acting film actuator, see whether the spring stiffness of the actuator matches the locator.
6, exclude whether the actuator has cylinder air, or cylinder leakage.
7. Exclude the positioner amplifier or piezoelectric valve airway weight whether there is dirt.
8, eliminate the valve friction is too large and positioner does not match the situation.
Common valve positioner classification and principle valve positioner according to the structure: Pneumatic valve positioner, electric valve positioner and intelligent valve positioner, is the main control valve accessories, usually with pneumatic control valve, it accepts the regulator output signal, and then to its output signal to control the pneumatic control valve, when the control valve, the valve stem of the displacement feedback to valve positioner and through mechanical device, The valve position is transmitted to the upper system by electrical signal.
Valve Positioner (Valve Positioner)
Valve positioner according to structure: Pneumatic valve positioner, electric valve positioner and intelligent valve positioner, is the main control valve accessories, usually with pneumatic control valve, it accepts the regulator output signal, and then to its output signal to control the pneumatic control valve, when the control valve, the valve stem of the displacement feedback to valve positioner and through mechanical device, The valve position is transmitted to the upper system by electrical signal.
(1) Structure
Valve positioner according to its structure form and working principle can be divided into pneumatic valve positioner, electric-gas valve positioner and intelligent valve positioner.
Valve positioner can increase the output power of the regulating valve, reduce the transmission lag of the regulating signal occurs, accelerate the movement speed of the valve stem, can 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 correct positioning of the regulating valve.
(2) locator classification
1, the valve positioner is divided into pneumatic valve positioner, electrical valve positioner and intelligent valve positioner according to the input signal.
(1) The input signal of the pneumatic valve positioner is the standard gas signal, for example, 20~100kPa gas signal, its output signal is also the standard gas signal.
(2) The input signal of the electrical valve positioner is the standard current or voltage signal, for example, 4~20mA current signal or 1~5V voltage signal, etc., the electrical signal is converted into electromagnetic force inside the electrical valve positioner, and then the output gas signal to the toggle control valve.
(3) intelligent electrical valve positioner it will control room output current signal into the drive regulating valve gas signal, according to the valve stem friction when working, offset medium pressure fluctuation and the unbalanced force, so that the valve opening corresponding to the control room output current signal. And the corresponding parameters can be set by intelligent configuration to improve the performance of the control valve.
2, according to the direction of the action can be divided into one-way valve positioner and two-way valve positioner. The one-way valve positioner is used in the piston actuator, the valve positioner only works in one direction, the two-way valve positioner works on both sides of the cylinder of the piston actuator, in two directions.
3, according to the valve positioner output and input signal gain symbol is divided into positive valve positioner and reaction valve positioner. As the input signal to the positive-acting valve positioner increases, the output signal also increases, so the gain is positive. Reaction valve positioner input signal increases, the output signal decreases, therefore, the gain is negative.
4, according to the valve positioner input signal is analog signal or digital signal, can be divided into ordinary valve positioner and field bus electrical valve positioner. The input signal of the common valve locator is the analog pressure or current, voltage signal, the input signal of the fieldbus electrical valve locator is the digital signal of the fieldbus.
5, according to whether the valve positioner with CPU can be divided into ordinary electrical valve positioner and intelligent electrical valve positioner. Common electrical valve positioners do not have CPU, therefore, do not have intelligence, can not handle the relevant intelligent operations. Intelligent electrical valve positioner with CPU, can deal with the intelligent operation, for example, can carry forward channel nonlinear compensation, etc., fieldbus electrical valve positioner can also take P>
6, according to the feedback signal detection method can also be classified.
For example, the valve positioner detects the valve position signal by the mechanical connecting rod method, the valve positioner detects the valve stem displacement by the Hall effect method, the valve positioner detects the valve stem displacement by the electromagnetic induction method, etc.
(3) Working principle
The valve positioner is the main accessory of the control valve. It takes the valve stem displacement signal as the input feedback measurement signal, takes the controller output signal as the setting signal, compares, when the two have the deviation, changes its output signal to the actuator, makes the actuator action, establishes the valve stem displacement and the controller output signal between the one-to-one correspondence. Therefore, the valve positioner consists of a feedback control system with the stem displacement as the measurement signal and the controller output as the setting signal. The control variable of the control system is the output signal of the valve positioner to the actuator.
(four) locator action principle
(1) used for regulating the important regulation system with high quality requirements, in order to improve the positioning accuracy and reliability of the regulating valve.
(2) for valve two ends of the pressure difference is large (¡÷p1MPa) occasions. By increasing the air source pressure, the output force of the actuator is increased to overcome the unbalance force produced by the liquid on the spool and reduce the stroke error.
(3) when the medium is adjusted for high temperature, high pressure, low temperature, toxic, flammable, explosive, in order to prevent external leakage, the packing is often pressed very tightly, so the friction between the valve stem and the packing is large, at this time, the locator can overcome the delay.
(4) When the medium is a viscous fluid or contains a solid suspended substance, the positioner can overcome the resistance of the medium to the movement of the stem.
(5) for large diameter (Dg100mm) regulating valve to increase the output thrust of the actuator.
(6) When the distance between the regulator and the actuator is above 60m, the positioner can overcome the transmission lag of the control signal and improve the reaction speed of the valve.
(7) used to improve the flow characteristics of the regulating valve.
(8) When a regulator controls two actuators to implement the division control, two positioners can be used to accept the low input signal and the high input signal respectively, then an actuator low range action, another elevation action, that is, constitutes the division adjustment.
(5) suitable varieties
Commonly used actuators are divided into pneumatic actuators, electric actuators, straight stroke, Angle stroke. Used to open and close all kinds of valves and air plates automatically and manually.
Post time: Sep-24-2022
