Fengquan·Electric regulating valve use and maintenance Abstract: This paper mainly introduces the installation precautions, common faults and causes analysis of electric control valves to ensure the correct use and maintenance of electric control valves. Black Garlic Powder is extracted from black garlic, it can be used in the production of black garlic cookies, capsule, baked goods, etc.
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With the rapid development of China's industry, electric control valves are more and more widely used in metallurgy, petrochemical and other fields, and their stability and reliability are becoming more and more important. The quality of their working conditions will directly affect the 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, in order to ensure that the regulating valve can work normally when driving and make the system operate safely, the new valve should first check whether the nameplate mark on the valve matches the design requirements before installation. At the same time, the following items should be debugged.
Basic error limit; full stroke deviation; hysteresis; dead zone; leakage (when required)
If the control valve in the original system is overhauled, in addition to the above-mentioned items, the sealing check of the stuffing box and joints of the old valve should be checked.
Many of the regulating valves are used in the field, which are 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 position and direction, or unclean pipes. Therefore, the electric control valve should pay attention to the following aspects when installing and using:
(1) The regulating valve belongs to the field instrument, and 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. Keep away from vibration sources or increase anti-vibration measures where there is a source.
(2) The regulating valve should generally be installed vertically. Under special circumstances, it can be tilted. If the tilt angle is large or the valve itself is too heavy, the support should be added to the valve.
(3) The pipe for installing the regulating valve should not be too high from the ground or the floor. When the pipe height is more than 2 m, the platform should be set as much as possible to facilitate the operation of the handwheel and easy maintenance.
(4) Before the installation of 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 avoid impurities jamming. After using the handwheel mechanism, you should return to the original neutral position.
(5) In order to make the production process continue in the event of failure or maintenance of the regulating valve, the regulating valve should be added with a bypass line.
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 in accordance with the relevant electrical equipment construction requirements. If it is a flameproof product, it should be installed in accordance with the requirements of the "Installation Specifications for Electrical Equipment in Explosive Hazardous Locations". For example, the field conductor adopts SBH type or other six-core or eight-core rubber outer diameter Φ11.3 mm rubber cable. In the use of maintenance, it is strictly forbidden to open the cover and repair the explosion-proof surface in the explosive place. At the same time, do not scratch or scratch the explosion-proof surface during disassembly and assembly, and restore it to the original explosion-proof requirement state after maintenance.
(7) After the gear unit of the actuator is disassembled, attention should be paid to lubrication. Low-speed motors are generally not required to be disassembled and refueled. After assembly, check that the valve position matches the valve position opening indication.
2 common fault locations and causes analysis
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.
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.
2.1 servo amplifier
When the servo amplifier is in normal working condition:
(1) When there is 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 II is 150 μA), the output load voltage is 205 to 220VAC.
(4) The output voltage is basically symmetrical.
If the servo amplifier does not work properly, each part may have the following conditions:
(1) Preamplifier
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 you can't zero, it might 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 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.
2.2 regulating valve
When the 4 to 20 mA 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 operation hand wheel feels abnormal
A. It feels too light. It may be that the handwheel pin 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 4~20 mA 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 ~ 20 mA signal, the control 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 sources nearby, 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.
3 Conclusion
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, which has considerable economic benefits for the enterprise's energy saving and consumption reduction.
