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Different types of regulating valves have different faults and their causes. Taking the straight-stroke electric regulating valve produced by Sichuan Instrument Factory as an example, the general fault and maintenance method of the electric regulating valve are explained.
1 When the servo amplifier servo amplifier is working normally:
(1) When there is no input signal, there should be no output voltage.
(2) Open-loop dead zone current ≤ 160?? A (type II is 100?? A).
(3) When the input signal is >240??A (type II is 150??A), the output load voltage is 205~220VAC.
(4) The output voltage is basically symmetrical.
If the servo amplifier does not work properly, each part may have the following conditions:
(1) When the preamplifier 1 has no signal input, the output of the double beat magnetic amplifier is adjusted to zero by the potentiometer W101. If you can't zero, it might be:
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 asymmetrical.
2 has an input signal, but no output or output asymmetry may be:
A. The voltage at the secondary end of the transformer B301 for the AC winding current is asymmetrical.
B. The resistance values ​​of resistors R110 and R111 are changed, and electrolytic capacitors C110 and C111 are damaged.
C. The AC excitation winding is short-circuited.
D. Some of the diodes D105 to 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 to change the polarity of the input signal, and the other side of the trigger has a pulse signal. The number of trigger pulses and the amplitude of the two groups should be basically the same. Otherwise there are the following situations.
1 No input signal (pre-magnetic amplifier is in normal working condition), 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 are extremely weak.
B, the resistance R204, R205, R208, R209 resistance changes.
2 There is an input signal, and there is no trigger pulse at the output, which may be:
A. The triode and the single junction Tube on the side without the output pulse are damaged.
B. The primary or secondary open or short circuit of the pulse transformer on the side without the output pulse.
C. The diode (D207 or D208) on the side without the output pulse is short-circuited.
3 The output trigger pulse is abnormal. There are several phenomena:
A. When there is no signal, the two sets of triggers have pulse output. After adding the signal, they are all normal. It may be the electrolytic capacitor C202 or C203.
B. The output of both sides of the trigger is normal. After working for a period of time, the output pulse gradually disappears, and there may be a problem with the single tube.
C, the output has positive and negative pulses, which may be diode D207, D208 is broken or soldered.
(3) After the above inspection and maintenance, the servo amplifier should work normally if there is no fault in the control loop. Otherwise there are two situations:
1 When there is no input signal, there is output voltage (voltage close to 220VAC) may be:
A. The thyristor SCR1 and SCR2 are damaged.
B. Capacitors C301 and C302 are broken down.
2 When there is an input signal, if there is no output signal or the output voltage is low, it may be:
A. The diodes D301 to D308 are broken down.
B. The thyristor SCR1 and SCR2 are damaged.
2 Regulating valve When the 4~20mA signal is input, the regulating valve stem can move up and down with the signal change within the rated stroke. If it does not work properly, there may be the following faults:
1 The operating hand wheel feels abnormal A, the feeling is too light, it may be that the handwheel bayonet is detached or broken.
B. I feel too heavy or can't move. There is a foreign body jam in the reducer; the valve core is stuck with the bushing or with the valve seat; the valve stem is severely bent.
2 Input 4~20mA signal, the regulating valve does not work.
A. The system wiring is incorrect.
B. The motor split phase capacitor CD is damaged.
C, the motor wiring is open.
D, the valve core is detached or the valve stem is broken (the actuator has action at this time)
3 Input 4~20mA signal, the regulating valve can not finish the rated stroke.
A. The position of the differential transformer is not adjusted.
B. Some of the diodes D701 to D712 are damaged.
C, transistor BG701 is damaged.
(4) Other failures during field use.
1 valve oscillates and screams.
A. The sensitivity is adjusted too high and the actuator generates oscillation.
B. The fluid pressure changes too much and the actuator thrust is insufficient.
C. The selection of the regulating valve is large, and the valve often works at a small opening.
D. The flow direction of the medium is consistent with the valve closing direction.
E, other nearby sources, the support is unstable.
F, the valve plug and bushing are seriously worn.
2 valve is slow.
A, the medium is too sticky, there is blockage or coking.
B. The filler is aged and the packing is pressed too tightly.
3 The amount of leakage is large.
A. The valve plug or seat is corroded and worn.
B. The seat is loose or the thread is corroded.
C, valve seat, valve core has foreign matter.
D. The starting point (electric opening type) or the end point (electric closing type) of the valve is not adjusted.
4 The filler and the upper and lower bonnet joints leak.
A. The packing gland is not pressed.
B, PTFE filler aging deterioration.
C, the stem is damaged.
D. The fastening nut is loose.
E. The gasket is damaged.
Analysis of Common Fault Locations and Causes of Electric Control Valves
The performance of the regulating valve will directly affect the working quality of the entire regulating system. Since the regulating valve is in direct contact with the medium to be tuned in the field, the working environment is very harsh, so it is easy to generate various faults. In the production process, in addition to eliminating these faults at any time, regular maintenance and regular maintenance must be carried out. Especially for the control valve with particularly harsh environment, more attention should be paid to maintenance and regular maintenance.