Basic knowledge of electric regulating valve

Precautions for installation and use Basic error limit; full stroke deviation; backlash; dead zone; If the control valve in the original system is overhauled, in addition to checking the above items, the sealing of the stuffing box and joints of the old valve should also be checked. In the field use of the control valve, many are often not caused by the quality of the control valve itself, but caused by improper installation and use of the control valve, such as improper installation environment, installation position and direction, or unclean pipelines. Therefore, the electric control valve should pay attention to the following aspects when installing and using: (1) The control valve belongs to the field instrument, and the ambient temperature is required to be in the range of -25 to 60 °C, and the relative humidity is less than or equal to 95%. If it is installed in the open air or in high temperature places, waterproof and cooling measures should be taken. Where there is a vibration source, keep away from the vibration source or increase anti-vibration measures. (2) The regulating valve should be installed vertically in general, and can be tilted under special circumstances. For example, when the tilt angle is large or the valve itself has too much weight, the valve should be protected by a support. (3) Generally, the pipeline for installing the regulating valve should not be too high from the ground or the floor. When the pipeline height is greater than 2m, a platform should be set up as much as possible to facilitate the operation of the handwheel and facilitate maintenance. (4) Before installing the regulating valve, the pipeline should be cleaned to remove dirt and welding slag. After installation, in order to ensure that impurities do not remain in the valve body, the valve should be cleaned again, that is, all valves should be opened when the medium is introduced to prevent impurities from getting stuck. After using the handwheel mechanism, it should return to the original neutral position. (5) In order to enable the control valve to continue the production process in the event of failure or maintenance, the control valve should be equipped with a bypass pipeline. At the same time, special attention should be paid to whether the installation position of the regulating valve meets the requirements of the process. 2. Analysis of common fault locations and causes The working performance of the regulating valve will directly affect the working quality of the entire regulating system. Because the regulating valve is in direct contact with the medium to be adjusted on site, the working environment is very harsh, so various failures are prone to occur. In the production process, in addition to eliminating these faults at any time, regular maintenance and regular maintenance must also be carried out. Especially for the control valve with particularly harsh environment, more attention should be paid to maintenance and regular maintenance. Different forms of regulating valves have different failures and their causes. Taking the straight-stroke electric regulating valve produced by Sichuan Instrument General Factory as an example, the general faults and maintenance methods of the electric regulating valve are explained. Servo amplifier When the servo amplifier is working normally: (1) When there is no input signal, there should be no output voltage. (2) The open-loop dead zone current is less than or equal to 160 μA (type II is 100 μA). (3) When the input signal is greater than 240 μA (150 μA for type II), the output load voltage is 205 to 220 V AC. (4) The output voltage is basically symmetrical. If the servo amplifier does not work normally, there may be the following situations for each part: (1) Pre-magnetic amplifier ① When there is no signal input, the output of the double-beat magnetic amplifier can be adjusted to zero through the potentiometer W101. If it cannot be adjusted to zero, it may be: A. Transformer W101 is desoldered or damaged. B. The resistors R110 and R111 and the electrolytic capacitors C101 and C102 are soldered or desoldered. C. Diodes D105~D108 are soldered or damaged. D. The offset current is abnormal. E. The AC winding is not symmetrical. ②There is input signal, but no output or output asymmetry may be: A. The secondary terminal voltage of transformer B301 for AC winding current is asymmetrical. B. The resistance values ​​of resistors R110 and R111 change, and the electrolytic capacitors C110 and C111 are damaged. C. The AC excitation winding is short-circuited. D. Some of the diodes D105~D108 are damaged or soldered. (2) When the trigger has input, one side of the trigger should have a pulse signal on the oscilloscope screen, and if the polarity of the input signal is changed, the other side of the trigger will have a pulse signal. The number and amplitude of trigger pulses in the two groups should be basically the same. Otherwise, there are the following situations. ①There is no input signal (the pre-magnetic amplifier is in normal working state), and there is a trigger pulse at the output, which may be: A. The triode on the output side of the trigger pulse is damaged, or the c and e poles are soldered. B. The resistance values ​​of resistors R204, R205, R208 and R209 have changed. ②There is an input signal, but there is no trigger pulse at the output, which may be: A. The triode and single-junction tube on the side without output pulse are damaged. B. The primary or secondary of the pulse transformer on the side with no output pulse is open or short-circuited. C. The diode (D207 or D208) on the side without output pulse is short-circuited. ③The abnormal output trigger pulse has the following phenomena: A. When there is no signal, the two sets of triggers have pulse output, and they are normal after adding the signal, which may be the electrolytic capacitor C202 or C203 soldering. B. The output on both sides of the trigger is normal at the beginning. After working for a period of time, the output pulse gradually disappears. There may be a problem with the single-junction tube. C. Positive and negative pulses appear in the output, it may be that the diodes D207 and D208 are broken down or soldered.
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