With the rapid development of China's industry, electric control valves have become more and more widely used in metallurgy, petrochemical, and other fields. Their stability and reliability have become more and more important, and their working status will directly affect automatic control. Process, this article will elaborate on the use and maintenance of the electric control valve.
1 Installation and Use Precautions The newly designed and installed control system should ensure that the regulating valve can work normally when the vehicle is started and the system is running safely. Before the new valve is installed, check whether the nameplate mark on the valve is consistent with the design requirements. At the same time, the following items should also be debugged.
Basic error limit; Full stroke deviation; Backlash; Dead zone;
If the overhaul of the regulating valve in the original system has been carried out, in addition to checking the above items, the sealing of the old valve's stuffing box and joints should be checked.
The use of regulating valves in the field is often caused not by the quality of the regulating valve itself, but by improper installation and use of the regulating valve, such as the installation environment, improper installation location and direction, or improper piping. Therefore, when the electric control valve is installed and used, pay attention to the following aspects:
(1) The regulating valve is a field instrument. It requires that the ambient temperature should be in the range of -25 to 60°C and the relative humidity is ≤ 95%. If it is installed in open air or high temperature, waterproof and cooling measures should be taken. Wherever there is a source of vibration, keep away from vibration sources or increase anti-vibration measures.
(2) The regulating valve should generally be installed vertically. In special circumstances, it can be tilted. If the angle of inclination is large or the valve itself is too heavy, the support of the valve should be increased.
(3) 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, the platform should be set as far as possible to facilitate the operation of the handwheel and facilitate the maintenance.
(4) The regulating valve should be cleaned before installation to remove dirt and welding slag. After installation, in order to ensure that no impurities remain in the valve body, the valve should be cleaned again, that is, all the valves should be opened when the medium is passed in, so as not to trap the impurities. After using the handwheel mechanism, it should be restored to its original neutral position.
(5) In order to allow the production process to continue in the event of a fault or maintenance of the regulating valve, a bypass line must be added to the regulating valve.
At the same time, special attention should be paid to whether the installation position of the regulating valve meets the requirements of the process.
(6) The electrical part of the electric control valve shall be installed according to the relevant electrical equipment construction requirements. If the explosion-proof products are to be installed in accordance with the requirements of the “Electrical Equipment Installation Criteria for Explosion Hazardous Locationsâ€. For example, SBH-type or other six-core or eight-core rubber-mounted cable with an outer diameter of Φ11.3mm is used for the field wiring. During use and maintenance, it is forbidden to open the lid and repair the explosion-proof surface in an explosive place. At the same time, do not injure or scratch the explosion-proof surface in the disassembly and assembly, and restore the original explosion-proof requirements after the maintenance.
(7) After the reducer of the actuator is removed, lubrication should be paid attention to, and the low-speed motor should not be disassembled and refueled. After installation, check whether the valve position and valve position opening indication match.
2 Common Fault Locations and Causes Analysis The 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 media being adjusted in the field, the working environment is very harsh, and therefore it is easy to produce various failures. In the production process, besides eliminating these faults at any time, regular maintenance and regular maintenance must be carried out. Especially for the use of a particularly bad control valve, it should pay more attention to maintenance and regular maintenance.
Different types of regulating valves have different faults and their causes. Taking the straight-stroke electric control valve produced by the Sichuan Instrument Factory as an example, the general failure and maintenance methods of the electric control valve will be described.
2.1 Servo Amplifier When the servo amplifier is operating normally:
(1) When there is no input signal, there should be no output voltage.
(2) Open loop dead-zone current ≤ 160μA (Type II is 100μA).
(3) When the input signal is >240μA (Type II is 150μA), the output load voltage is 205 to 220VAC.
(4) The output voltage is basically symmetrical.
If the servo amplifier is not working properly, the following conditions may occur in each part:
(1) When the pre-amplifier 1 has no signal input, the output of the two-shot magnetic amplifier can be adjusted to zero by the potentiometer W101. If you can't zero, you may be:
A. Detachment or damage of transformer W101.
B. Welded or de-welded resistors R110 and R111 and electrolytic capacitors C101 and C102.
C. Welded or damaged diodes D105 to D108.
D. The offset current is abnormal.
E. AC winding asymmetry.
2 There is an input signal, but no output or output asymmetry may be:
A. Transformer B301 provides asymmetrical secondary-side voltage for AC winding currents.
B. The resistances of the resistors R110 and R111 change, and the electrolytic capacitors C110 and C111 are damaged.
C, AC excitation winding short circuit.
D. Some of the diodes D105 to D108 are damaged or have been welded.
(2) When the trigger has an input, one of the triggers should have a pulse signal on the oscilloscope screen, change the polarity of the input signal, then the other trigger has a pulse signal. The number and amplitude of the two sets of trigger pulses should be basically the same. Otherwise there are the following situations.
1 There is no input signal (preamplifier is in normal operation) and the output has a trigger pulse, which may be:
A. There is damage to the triode on the trigger pulse output side, or c, e extremely cold.
B, resistance R204, R205, R208, R209 resistance changes.
2 There is an input signal, the output has no trigger pulse, may be:
A. Transistor and single junction tube on the side without output pulse are damaged.
B. The primary or secondary open or short circuit of the pulse transformer on the side of no output pulse.
C. The diode on the output pulse side (D207 or D208) is short-circuited.
3 The output trigger pulse does not have the following 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 welding of 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 problems with the single junction tube.
C. Positive and negative pulses appear on the output. The diodes D207 and D208 may be broken down or soldered.
(3) After the above inspection and maintenance, the servo amplifier should be able to work normally if there is no fault in the control circuit. Otherwise there are two situations:
1 When there is no input signal, the output voltage (voltage close to 220VAC) may be:
A, thyristor SCR1, SCR2 is damaged.
B. The capacitors C301, C302 are broken down.
2 When there is an input signal, no output signal or output voltage is low, it may be:
A. There are breakdowns in the diodes D301 to D308.
B. The thyristor SCR1 and SCR2 are damaged.
2.2 Regulating valve When inputting 4 ~ 20mA signal, the valve stem of the regulating valve can move up and down freely with the signal within the rated stroke. If it does not work properly, the following problems may occur:
1 Operation Hand wheel feels abnormal A. The feeling is too light. It may be that the hand wheel locking pin is detached or broken.
B. Feeling too heavy or spinning. Foreign material stuck in the reducer; the valve plug and the bushing or the valve seat are stuck; the valve stem is seriously bent.
2 Input 4 ~ 20mA signal, control valve does not move.
A. The system wiring is incorrect.
B. The motor phase separation capacitor CD is damaged.
C, motor wiring open circuit.
D. The valve core is detached or the valve stem is broken (at this time, the actuator has an action)
3 Input 4 ~ 20mA signal, adjust the valve can not complete the rated travel.
A. The position of the differential transformer is not adjusted.
B. Some of the diodes D701 to D712 are damaged.
C. The transistor BG701 is damaged.
(4) Other failures at the site.
1The valve oscillates and tweets.
A. The sensitivity is adjusted too high and the actuator is oscillating.
B. Fluid pressure changes too much and actuator thrust is insufficient.
C. Large selection of regulating valve, valves often work at small opening degree.
D. The direction of flow of the medium is the same as the direction of valve closing.
E. The influence of other nearby earthquake sources is not stable.
F. The valve plug and bushing wear badly.
2 The valve is dull.
A, medium viscosity is too large, there is a blockage or coking phenomenon.
B, filler aging, packing pressure too tight.
3 large amount of leakage.
A. The valve plug or valve seat is corroded and worn.
B. The valve seat is loose or the thread is corroded.
C. There are foreign objects on the valve seat and spool.
D. The starting point of the valve (electrically open) or the end (electrically closed) is not adjusted.
4 The packing and the upper and lower bonnet joints leak.
A. The packing gland is not pressed.
B, aging PTFE filler deterioration.
C. The stem is damaged.
D. Loosen the fastening nut.
E. The gasket is damaged.
3 Concluding remarks The correct use and maintenance of the electric control valve can not only improve the reliability of the process control, but also increase the service life of the electric control valve. It has considerable economic benefits for the enterprise's energy saving and consumption reduction.
1 Installation and Use Precautions The newly designed and installed control system should ensure that the regulating valve can work normally when the vehicle is started and the system is running safely. Before the new valve is installed, check whether the nameplate mark on the valve is consistent with the design requirements. At the same time, the following items should also be debugged.
Basic error limit; Full stroke deviation; Backlash; Dead zone;
If the overhaul of the regulating valve in the original system has been carried out, in addition to checking the above items, the sealing of the old valve's stuffing box and joints should be checked.
The use of regulating valves in the field is often caused not by the quality of the regulating valve itself, but by improper installation and use of the regulating valve, such as the installation environment, improper installation location and direction, or improper piping. Therefore, when the electric control valve is installed and used, pay attention to the following aspects:
(1) The regulating valve is a field instrument. It requires that the ambient temperature should be in the range of -25 to 60°C and the relative humidity is ≤ 95%. If it is installed in open air or high temperature, waterproof and cooling measures should be taken. Wherever there is a source of vibration, keep away from vibration sources or increase anti-vibration measures.
(2) The regulating valve should generally be installed vertically. In special circumstances, it can be tilted. If the angle of inclination is large or the valve itself is too heavy, the support of the valve should be increased.
(3) 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, the platform should be set as far as possible to facilitate the operation of the handwheel and facilitate the maintenance.
(4) The regulating valve should be cleaned before installation to remove dirt and welding slag. After installation, in order to ensure that no impurities remain in the valve body, the valve should be cleaned again, that is, all the valves should be opened when the medium is passed in, so as not to trap the impurities. After using the handwheel mechanism, it should be restored to its original neutral position.
(5) In order to allow the production process to continue in the event of a fault or maintenance of the regulating valve, a bypass line must be added to the regulating valve.
At the same time, special attention should be paid to whether the installation position of the regulating valve meets the requirements of the process.
(6) The electrical part of the electric control valve shall be installed according to the relevant electrical equipment construction requirements. If the explosion-proof products are to be installed in accordance with the requirements of the “Electrical Equipment Installation Criteria for Explosion Hazardous Locationsâ€. For example, SBH-type or other six-core or eight-core rubber-mounted cable with an outer diameter of Φ11.3mm is used for the field wiring. During use and maintenance, it is forbidden to open the lid and repair the explosion-proof surface in an explosive place. At the same time, do not injure or scratch the explosion-proof surface in the disassembly and assembly, and restore the original explosion-proof requirements after the maintenance.
(7) After the reducer of the actuator is removed, lubrication should be paid attention to, and the low-speed motor should not be disassembled and refueled. After installation, check whether the valve position and valve position opening indication match.
2 Common Fault Locations and Causes Analysis The 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 media being adjusted in the field, the working environment is very harsh, and therefore it is easy to produce various failures. In the production process, besides eliminating these faults at any time, regular maintenance and regular maintenance must be carried out. Especially for the use of a particularly bad control valve, it should pay more attention to maintenance and regular maintenance.
Different types of regulating valves have different faults and their causes. Taking the straight-stroke electric control valve produced by the Sichuan Instrument Factory as an example, the general failure and maintenance methods of the electric control valve will be described.
2.1 Servo Amplifier When the servo amplifier is operating normally:
(1) When there is no input signal, there should be no output voltage.
(2) Open loop dead-zone current ≤ 160μA (Type II is 100μA).
(3) When the input signal is >240μA (Type II is 150μA), the output load voltage is 205 to 220VAC.
(4) The output voltage is basically symmetrical.
If the servo amplifier is not working properly, the following conditions may occur in each part:
(1) When the pre-amplifier 1 has no signal input, the output of the two-shot magnetic amplifier can be adjusted to zero by the potentiometer W101. If you can't zero, you may be:
A. Detachment or damage of transformer W101.
B. Welded or de-welded resistors R110 and R111 and electrolytic capacitors C101 and C102.
C. Welded or damaged diodes D105 to D108.
D. The offset current is abnormal.
E. AC winding asymmetry.
2 There is an input signal, but no output or output asymmetry may be:
A. Transformer B301 provides asymmetrical secondary-side voltage for AC winding currents.
B. The resistances of the resistors R110 and R111 change, and the electrolytic capacitors C110 and C111 are damaged.
C, AC excitation winding short circuit.
D. Some of the diodes D105 to D108 are damaged or have been welded.
(2) When the trigger has an input, one of the triggers should have a pulse signal on the oscilloscope screen, change the polarity of the input signal, then the other trigger has a pulse signal. The number and amplitude of the two sets of trigger pulses should be basically the same. Otherwise there are the following situations.
1 There is no input signal (preamplifier is in normal operation) and the output has a trigger pulse, which may be:
A. There is damage to the triode on the trigger pulse output side, or c, e extremely cold.
B, resistance R204, R205, R208, R209 resistance changes.
2 There is an input signal, the output has no trigger pulse, may be:
A. Transistor and single junction tube on the side without output pulse are damaged.
B. The primary or secondary open or short circuit of the pulse transformer on the side of no output pulse.
C. The diode on the output pulse side (D207 or D208) is short-circuited.
3 The output trigger pulse does not have the following 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 welding of 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 problems with the single junction tube.
C. Positive and negative pulses appear on the output. The diodes D207 and D208 may be broken down or soldered.
(3) After the above inspection and maintenance, the servo amplifier should be able to work normally if there is no fault in the control circuit. Otherwise there are two situations:
1 When there is no input signal, the output voltage (voltage close to 220VAC) may be:
A, thyristor SCR1, SCR2 is damaged.
B. The capacitors C301, C302 are broken down.
2 When there is an input signal, no output signal or output voltage is low, it may be:
A. There are breakdowns in the diodes D301 to D308.
B. The thyristor SCR1 and SCR2 are damaged.
2.2 Regulating valve When inputting 4 ~ 20mA signal, the valve stem of the regulating valve can move up and down freely with the signal within the rated stroke. If it does not work properly, the following problems may occur:
1 Operation Hand wheel feels abnormal A. The feeling is too light. It may be that the hand wheel locking pin is detached or broken.
B. Feeling too heavy or spinning. Foreign material stuck in the reducer; the valve plug and the bushing or the valve seat are stuck; the valve stem is seriously bent.
2 Input 4 ~ 20mA signal, control valve does not move.
A. The system wiring is incorrect.
B. The motor phase separation capacitor CD is damaged.
C, motor wiring open circuit.
D. The valve core is detached or the valve stem is broken (at this time, the actuator has an action)
3 Input 4 ~ 20mA signal, adjust the valve can not complete the rated travel.
A. The position of the differential transformer is not adjusted.
B. Some of the diodes D701 to D712 are damaged.
C. The transistor BG701 is damaged.
(4) Other failures at the site.
1The valve oscillates and tweets.
A. The sensitivity is adjusted too high and the actuator is oscillating.
B. Fluid pressure changes too much and actuator thrust is insufficient.
C. Large selection of regulating valve, valves often work at small opening degree.
D. The direction of flow of the medium is the same as the direction of valve closing.
E. The influence of other nearby earthquake sources is not stable.
F. The valve plug and bushing wear badly.
2 The valve is dull.
A, medium viscosity is too large, there is a blockage or coking phenomenon.
B, filler aging, packing pressure too tight.
3 large amount of leakage.
A. The valve plug or valve seat is corroded and worn.
B. The valve seat is loose or the thread is corroded.
C. There are foreign objects on the valve seat and spool.
D. The starting point of the valve (electrically open) or the end (electrically closed) is not adjusted.
4 The packing and the upper and lower bonnet joints leak.
A. The packing gland is not pressed.
B, aging PTFE filler deterioration.
C. The stem is damaged.
D. Loosen the fastening nut.
E. The gasket is damaged.
3 Concluding remarks The correct use and maintenance of the electric control valve can not only improve the reliability of the process control, but also increase the service life of the electric control valve. It has considerable economic benefits for the enterprise's energy saving and consumption reduction.
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