The effect of pneumatic valve positioner pneumatic valve closed the main reasons and solutions

The effect of pneumatic valve positioner pneumatic valve closed the main reasons and solutions

Valve positioner (also called: Pneumatic valve positioner) is an important part to adjust the valve, usually used with pneumatic self-actuating control valve, it is actuated by the output signal of the controller, and with its output signal to control the self-actuating control valve, when the control valve position, the stem offset is also fed back to the valve positioner by electronic device, Valve position is sent to the on-stage system software according to the electrical signal.
Valve positioner (also called: Pneumatic valve positioner) is an important part to adjust the valve, usually used with pneumatic self-actuating control valve, it is actuated by the output signal of the controller, and with its output signal to control the self-actuating control valve, when the control valve position, the stem offset is also fed back to the valve positioner by electronic device, Valve position is sent to the on-stage system software according to the electrical signal. Valve positioner structure: valve positioner according to the structure and principle can be divided into pneumatic valve positioner, electric-gas valve positioner intelligent valve positioner. Valve positioner can expand the adjustment valve output power, reduce the adjustment signal transmission lag, accelerate the stem speed, can improve the linear valve, get rid of the stem friction force and remove the influence of unbalanced force, fully ensure the correct and accurate positioning of the adjustment valve. Valve positioner compatible type common actuator pneumatic actuator, electric actuator, direct stroke arrangement, Angle stroke arrangement difference.
Used for automatic, manual type open and close all kinds of valves, fans, etc. Valve positioner is an important part of pressure regulating valve. The valve stem offset signal is regarded as the input feedback accurate measurement signal, and the output signal of the control board is regarded as the setting signal for comparison. When the two are different, the output signal to the actuator is changed to make the actuator position, and the one-to-one correspondence between the valve stem offset times and the output signal of the control board is set up.
Therefore, the valve positioner constitutes a feedback control system with stem offset as the accurate measurement signal and the output of the control board as the setting signal. The control variable of the control system is the output signal of the valve positioner to the actuator. Valve positioner key into the signal is divided into pneumatic valve positioner and electrical equipment valve positioner. Pneumatic valve positioner input signal is a standard gas signal, for example, 20~100kPa gas signal, its output signal is also a typical gas signal. Electrical equipment valve positioner input signal is a standard electrical flow or working voltage signal, such as 4~20mA electrical flow signal or 1~5V working voltage signal, electrical equipment valve positioner internal structure will be converted into magnetic field force, and then output gas signal to the rotary pressure regulating valve. According to the position direction can be divided into single valve positioner and double valve positioner.
Unilateral valve positioner with piston machine actuator, valve positioner only one position plays a role, double valve positioner acts on both sides of the piston machine actuator cylinder, play a role in two routes. According to the valve positioner output and the gain value of the input signal marked into positive effect valve positioner and reaction valve positioner.
When the input signal of the positive-effect valve positioner is raised, the output signal is also increased, so that the gain value is positive.
When the input signal of the reaction valve positioner is raised, the output signal is reduced and the gain value is negative. According to the valve positioner input signal is simulation signal or data signal, can be divided into general valve positioner and computer interface electrical equipment valve positioner.
General valve positioner type signal is the simulation of standard pressure or electrical flow, working voltage signal, computer interface electrical equipment valve positioner type signal is the computer interface digital signal. According to the valve positioner is not with CPU can be divided into general electrical equipment valve positioner and intelligent electrical valve positioner.
General electrical equipment valve positioner does not have CPU, therefore, does not have intelligent, can not solve the relevant intelligent calculation. Intelligent valve positioner with CPU, can solve the related intelligent calculation, such as sperm activity rate channel discrete system compensation, computer interface electrical equipment valve positioner can also take PID and other program modules, complete the corresponding calculation. Pneumatic valve closed the main reasons and solutions first of all, let’s analyze the self-operated valve pneumatic valve closed is what causes the valve to have a certain amount of leakage, to see whether the leakage of the valve is higher than the standard value, beyond is the product quality problem. Second, the electrical converter output is not paired with the valve film head working pressure. Whether the valve is stuck in dirt.
Valve first of all, let’s analyze the self-operated valve pneumatic valve closed is what causes the door to have a certain amount of leakage, to see whether the leakage of the valve is higher than the standard value, beyond is the product quality problem. Second, the electrical converter output is not paired with the valve film head working pressure. Whether the valve is stuck in dirt.
The valve spring force does not fit properly. Whether the stem is stuck.
Valve core, high pressure gate valve partial wear film head valve disc leakage steam.
Common positioning device faults.
Air opening valve, zero torsion spring axial force is too large. The stem is too short.
Adjust the valve before and after the pressure difference is too big, what is the problem of model selection.
Whether the actuator output force is too small, adjustable large reasonable output working pressure (PF to expand the output force, for the gas closing valve, the left rotation of the adjustment part (loose), that is, PO~PL shift, but need to pay attention to the change of the full stroke arrangement No.
We can first find the reason and apply the solution from the above statement. If you have a manual pneumatic valve, then every time suspended, let everyone must swing dead, but also let the dashboard staff, calibrate again, the zero and positioning instrument calibration again; There are many reasons why the closing position travel arrangement is not in place, the valve stem is partial wear, and the compressed gas pressure is up to standard. First, set the value of the valve positioner, and then adjust the closing position travel arrangement; Valves are air – open or air – close valves. If it is a gas valve, can see the pneumatic valve working pressure, positioning instrument zero measuring range adjustment has no problem, in addition, there is no card valve. If it is the gas open valve, the pneumatic valve is broken off, the valve should be closed. If it is not closed, it may be that the valve oil circuit plate has no dirty things stuck; If the valve is accidentally closed, it is proposed to inquire whether the pressure of the instrument panel is enough, that is, whether the pressure output of the locator can adjust the working pressure of the valve closed; Look at the working pressure of the pneumatic valve is not enough, and then look at the valve whether there is a card condition, or leakage, also closed.
More appropriate first style positioning device try; Air valve: 1, the axial force of the spring is insufficient, it can be appropriately increased. 2, the working condition permits, the valve should be removed to do a pressure test, take this opportunity to check the sealing condition of the valve core high pressure gate valve, and whether there is damage to the valve core and high pressure gate valve.
3. If the case of not closing again occurs, the valve can be cut out to check whether there are dirty things at the high pressure gate valve of the valve heart. 4. 1. The axial force of the spring is very large, which can be appropriately reduced. 2.
3, if the situation again appears close not dead, can cut out the valve, check whether there are dirty things at the valve heart high pressure gate valve 4, check the valve pneumatic valve working pressure is not wrong 5, check whether there is damage to the valve disc 6, check whether the zero point of the valve is higher if the work is carried out after the phenomenon of close not dead, It is proposed to check the main parameters of the valve to see if there is any difference between the customized main parameters and the actual working condition.