Electric control valve use and maintenance

With the rapid development of our country's industry, the application of electric control valve in metallurgy, petrochemical and other fields is becoming more and more widespread. Its stability and reliability are also becoming more and more important. Its working status will directly affect the automatic control Process, this article will elaborate on the use of electric control valve and maintenance. 1. Installation and application precautions Newly designed and installed control system, in order to ensure that the regulating valve can work normally while driving, and make the system run safely, the new valve should be installed before checking whether the nameplate mark on the valve is consistent with the design requirements . The following items should also be debugged. Basic error limit; full stroke deviation; backlash; dead zone; leakage (in demanding occasions). If the original system is overhauled control valve, in addition to the above-mentioned verification, but also the old valve should be stuffing box and connections and other parts of a tightness check. Regulating valve in the field of use, often not because of the quality of the control valve itself, but rather caused by the improper installation of the control valve, such as the installation environment, the installation location and direction of improper or unclear pipe and other causes. Therefore, the installation of electric control valve should pay attention to the following aspects: (1) The regulating valve is a field instrument, the ambient temperature should be -25 ~ 60 ℃, relative humidity ≤ 95%. If it is installed in open air or high temperature occasions, should take waterproof, cooling measures. In the place with the source to stay away from the vibration source or increase the anti-vibration measures. (2) The control valve should generally be installed vertically, under special circumstances can be tilted, such as a large tilt angle or the valve itself is too heavy when the valve should be increased support protection. (3) Generally, do not install the control valve pipe from the ground or the floor is too high, the pipe height is greater than 2m should be set as the platform, in order to facilitate the operation of the hand wheel and easy maintenance. (4) The control valve should be installed before cleaning the pipeline to remove dirt and welding slag. After installation, in order to ensure that no impurities remain in the valve body, the valve should also be cleaned again, that is, the medium should be opened so that all valves open to prevent impurities stuck. After using the hand wheel mechanism should be restored to the original neutral position. (5) In order to make the control valve in the event of failure or maintenance of the production process can continue, the control valve should be bypassed. At the same time should also pay special attention to the installation position of the valve is in line with the process requirements. (6) The electric part of the electric control valve should be installed according to the requirements of the electrical equipment construction. In the case of explosion-proof products, they should be installed in accordance with the "Installation Specification for Electrical Equipment in Explosion Hazardous Locations". Such as the scene wire SBH or other six-core or eight core, outer diameter of about Φ11.3mm rubber mounting cable. In the use of maintenance, in the explosive place is strictly prohibited open cover repair and blasting face pry. At the same time do not knock in the disassembly or scratch explosion-proof surface, after repair to restore the original flameproof state. (7) After the actuator reducer repair should pay attention to refueling lubrication, low-speed motor generally do not demolition and refueling. Assembly should also check the valve position and valve position opening instructions are consistent. 2. Common Fault Location and Analysis of the reasons for the performance of the control valve will directly affect the quality of the entire regulatory system. As the regulating valve in the field is in direct contact with the medium to be adjusted, the working environment is very poor, so easy to produce a variety of failures. In the production process, in addition to ruled out these failures at any time, but also must be regular maintenance and regular maintenance. Especially for the use of particularly harsh environment control valve, but should pay attention to maintenance and regular maintenance. Different forms of control valve, the failure and its causes are not the same. Sichuan Instrument Factory is now produced straight stroke electric control valve as an example to illustrate the general failure of electric control valve and maintenance methods. 2.1. Servo amplifier Servo amplifier normal working state: (1) no input signal, there should be no output voltage. (2) Open-loop dead-zone current ≤160 μA (Type Ⅱ is 100 μA). (3) When the input signal is> 240 μA (type 150 μA), the output load voltage is 205 to 220V AC. (4) The output voltage is basically symmetrical. If the servo amplifier is not working properly, each part may have the following situations: (1) Front magnetic amplifier ① When there is no signal input, the output of the dual-shot magnetic amplifier can be adjusted to zero through the potentiometer W101. Can not be zero may be: A. Transformer W101 desoldering or damaged. B. Resistance R110, R111 and electrolytic capacitors C101, C102 Weld or desoldering. C. Diode D105 ~ D108 Weld or damaged. D. Offset current is not normal. E. AC winding asymmetry. ② There is input signal, but no output or output asymmetry may be: A. Transformer B301 for the AC winding current secondary voltage asymmetry. B. Resistors R110 and R111 have resistance changes, electrolytic capacitors C110, C111 damaged. AC AC excitation winding short circuit. D. Diode D105 ~ D108 in some of the tube damage or Weld. (2) Trigger input, the trigger on one side of the oscilloscope screen should have a pulse signal, change the polarity of the input signal, then the other side of the trigger pulse signal. The trigger pulse number and amplitude of two groups should be basically the same. Otherwise there are the following situations. ① no input signal (pre-magnetic amplifier in normal working condition), the output trigger pulse may be: A. There trigger pulse output side of the transistor damage, or c, e very Weld. B. Resistance R204, R205, R208, R209 resistance has changed. ② there is input signal, the output without trigger pulse, may be: A. No output pulse side of the transistor, single junction tube damage. B. Pulsed transformer primary or secondary open circuit or short circuit without output pulse. C. No output pulse side of the diode (D207 or D208) short circuit. ③ output pulse is not normal trigger the following phenomena: A. No signal when the two sets of triggers have a pulse output, plus signals are normal, electrolytic capacitors may be C202 or C203 Weld. B. start the trigger on both sides of the output are normal, after a period of work, the output pulse gradually disappear, there may be a single junction problems. C. Positive and negative pulse output, the diode may be D207, D208 was punctured or Weld. (3) After the above inspection and maintenance, the servo amplifier should work normally without any fault in the control loop. Otherwise, there are the following two cases: ① Without input signal, the output voltage (voltage approaching 220VAC) may be: A. Thyristor SCR1, SCR2 damage. B. Capacitors C301, C302 are breakdown. ② there is no input signal, no output signal or the output voltage is low, it may be: A. D301 ~ D308 diode breakdown. B. SCR SCR1, SCR2 damage. 2.2 regulating valve When the input 4 ~ 20 mA signal, regulating valve stem in the rated stroke with the signal changes up and down freely. If it can not operate normally, it may have the following faults: ① The operating hand wheel feels abnormal. A. Feeling too light, it may be that the handwheel latch is off or broken. B. Feeling too heavy or too swirling. There is a foreign body in the reducer jam; spool and bushing or stuck with the valve seat; stem serious bending. ② input 4 ~ 20 mA signal, the control valve does not move. A. system wiring is wrong. B. Motor phase-split capacitor CD is damaged. C. Motor wiring is open. D. spool off or stem breakage (at this time the actuator has an action) ③ input 4 ~ 20 mA signal, the control valve can not go through the rated travel. A. Differential transformer position is not adjusted. B. diodes D701 ~ D712 in some damaged. C. Transistor BG701 damaged. (4) other failures in the field. ① valve turbulence, tweets. A. The sensitivity is too high and the actuator oscillates. B. Fluid pressure changes too much, the actuator thrust is not enough. C. control valve selection is large, the valve often work in a small opening. D. The flow direction of the medium is in the same direction as the valve is closed. E. Other sources near the impact of instability. F. Spool and bushings worn badly. ② valve slow action. A. medium viscosity is too large, there is congestion or coking phenomenon. B. Filler aging, packing pressed too tight. ③ large amount of leakage. A. Spool or seat is corroded and worn. B. Seat is loose or thread is corroded. C. Seat, spool foreign body. D. The starting point of the valve (electrical open) or the end (electrical closed) is not adjusted. ④ packing and the upper and lower bonnet junction leakage. A. packing gland did not compress. B. PTFE filler aging deterioration. C. Stem damage. D. Tightening nut loose. E. gasket is damaged. 3. Conclusion The correct use of electric control valve and maintenance, not only can improve the reliability of process control, but also increase the service life of electric control valve, the enterprise's energy saving has significant economic benefits.

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