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. 2.1 Servo amplifier Servo amplifier normal working condition: (1) no input signal, there should be no output voltage. (2) Open loop dead zone current ≤160μA (Ⅱ type is 100μA). (3) When the input signal is> 240μA (type 150μA), the output load voltage is 205 ~ 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 ①When 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, W101 desoldering transformer or damaged. B, resistance R110, R111 and electrolytic capacitors C101, C102 Weld or desoldering. C, diodes D105 ~ D108 Weld or damaged. D, the 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, the resistance of the resistors R110 and R111 has changed, the electrolytic capacitors C110, C111 damaged. C, 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. ①no input signal (front magnetic amplifier in normal working condition), the output trigger pulse may be: A, trigger pulse output side of the transistor damage, or c, e very Weld. B, resistance R204, R205, R208, R209 resistance has changed. ② input signal, the output without trigger pulse, may be: A, no output pulse side of the transistor, single junction tube damage. B, no output pulse side of the pulse transformer primary or secondary open circuit or short circuit. C, no output pulse side of the diode (D207 or D208) short circuit. The output trigger pulse is not normal There are several phenomena: A, no signal when the two sets of triggers have a pulse output, plus the signal are normal, may be electrolytic capacitors C202 or C203 Weld. B, the beginning of the trigger output on both sides are normal, after a period of work, the output pulse gradually disappear, monosomy tube may have problems. C, the output appears positive and negative pulses, it may be diode 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: ①Without input signal, the output voltage (voltage approaching 220VAC) may be: A, thyristor SCR1, SCR2 damage. B, the capacitor C301, C302 is breakdown. ② When there is input signal, there is no output signal or the output voltage is low, it may be: A, D301 ~ D308 diodes have breakdown. B, thyristor SCR1, SCR2 damage. 2.2 regulating valve When the input 4 ~ 20mA signal, the 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: ①The operating handwheel feels abnormal. A. It feels too light. It may be that the handwheel latch is off or broken. B, feeling too heavy or spinning. There are foreign objects in the reducer jam; spool and bushing or seat stuck; serious bending stem. ② input 4 ~ 20mA signal, the control valve does not move. A, the system wiring is wrong. B, the motor phase-split capacitor CD is damaged. C, motor wiring open. D, the spool off or stem breakage (at this time the actuator has an action) ③ input 4 ~ 20mA signal, regulating valve can not go through the rated travel. A, differential transformer position is not adjusted. B, some of the diodes D701 ~ D712 are damaged. C, transistor BG701 damaged. (4) other failures in the field. ①valve turbulence, tweets. A, the sensitivity is too high, the implementing agencies have oscillations. B, the fluid pressure changes too much, the actuator thrust is not enough. C, the choice of control valve, the valve often work in a small opening. D, the direction of flow of medium and valve closing direction. E, near the impact of other sources, support instability. F, spool and bushing wear serious. ② valve slow action. A, the media is too viscous, clogging or coking phenomenon. B, filler aging, packing pressed too tight. ③ large amount of leakage. A, spool or valve seat is corroded and worn. B, the seat is loose or the thread is corroded. C, seat, spool foreign body. D, the valve starting point (electric open) or the end (electric 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, tighten the nut loose. E, seal damage.