With the rapid development of China's industry, the electric control valve in metallurgy, petroleum and chemical industry applications more widely, its stability, reliability has become increasingly important, it's good or bad working conditions will directly affect the automatic control process, this article will elaborate on the use of electric control valves and maintenance.
1. Installation Notes
The new design and installation of control systems, in order to ensure that the control valve while driving to work when you can make the safe operation of the system, the new valve is installed, you should first check whether the valve on the nameplate marking in line with the design requirements. At the same time the following items should also be debugged.
Basic error limit; full itinerary deviation; hysteresis; dead zone; leakage (on the occasions when demanding).
If this is the original system, regulating valve repair carried out, in addition to the above for verification, but also deal with the old valve stuffing and sealing joints and other parts to check.
Regulating valve used in the field, many are not because of quality control valve itself is caused by, but the installation of the control valve caused by improper use, such as the installation environment, installation, or improper location and direction of the pipeline due to unclean and other reasons. Therefore, the use of electric control valve is installed when you pay attention to the following aspects:
(1) control valve are on-site instruments, the Environment and temperature should be in the range of -25 ~ 60 ℃, relative humidity ≤ 95%. If it is installed in the open air or high-temperature occasion, to take water, cooling measures. In a place away from local oscillator source or increase the anti-vibration measures.
(2) regulating valve should normally be installed vertically under special circumstances can be tilted, such as the tilt angle or the valve itself is much too large weight bearing parts of the valve should be increased protection.
(3) installation of the pipeline control valve generally not from the ground or floor is too high, taller than 2m in the pipeline should be possible to set a platform to facilitate the manipulator wheel and easy maintenance.
(4) The regulating valve installed before the piping should be cleaned to remove dirt and weld slag. After installation, to ensure not to impurities left in the valve body, the valve should be cleaned again, that pass into the media so that all valves should be open in order to avoid impurities stuck. The use of hand wheel mechanism, the gap should be restored to its original position.
(5) In order to control valve in the event of failure or maintenance of the case make the production process can continue, control valve should be added to by-pass pipeline.
At the same time should also pay particular attention to valve installation location is consistent with process requirements.
(6) The electric control valve installation of the electrical part of the construction of electrical equipment shall be in accordance with relevant requirements. The case of explosion-proof products should be "an explosion in hazardous electrical equipment installation specification" requirement to install it. If on-site use of SBH-type wire or other six core or 8 core, outside diameter of about Φ11.3mm rubber installation cables. In the use and maintenance, in the explosive power off Cap maintenance of premises and the non-explosion-proof surface to pry fighting. Do not knock the same time, disassembly, or scratch injury flameproof surface, repair and after going to restore the original state of explosion-proof requirements.
(7) The executive body of the reducer overhaul should be noted that, after lubrication, low-speed motor fuel in general do not take apart and wash. It should also check the assembled valve position and valve position opening directions match.
2. Common causes of failure location and analysis
The quality of the work of control valve performance will directly affect the whole quality of the work-conditioning system. As the regulating valve in the field is in direct contact with the medium being transferred, and the work environment is very bad, so prone to failure. In the production process, in addition to always exclude these failures, but also the need for regular maintenance and periodic overhaul. In particular, the use of environment, especially the poor control valve, but also should attach importance to the maintenance and periodic overhaul.
Different forms of control valve, its failures and its causes is not the same. Sichuan Instrument Factory is the production of straight stroke electric control valve as an example to illustrate the general electric control valve fault and repair methods.
2.1 Servo Amplifiers
Servo amplifier normal working state:
(1) No input signal there should be no output voltage.
(2) open-loop dead-zone current ≤ 160μA (Ⅱ type is 100μA).
(3) The input signal> 240μA (Ⅱ type of 150μA), the output load voltage? 205 ~ 220V? AC.
(4) the output voltage are essentially symmetrical.
If the servo amplifier is not working properly, then there may be various parts of the following situations:
(1) Pre-magnetic amplifier
① No signal input, dual-film magnetic amplifier output through the potentiometer W101 adjustable to zero. Can not be zero this may be:
A, transformer W101 Sealing-off or damaged.
B, resistors R110, R111, and electrolytic capacitors C101, C102 cold solder joint or Sealing-off.
C, diode D105 ~ D108 cold solder joint or damage.
D, offset current is not normal.
E, the exchange of winding asymmetry.
② an input signal, but no output or output of asymmetry may be:
A, transformer winding currents for the exchange of B301 secondary terminal voltage asymmetry.
B, resistors R110 and R111 of the resistance has changed, electrolytic capacitors C110, C111 damage.
C, AC magnetizing winding short-circuit.
D, diode D105 ~ D108 in the individual tube is damaged or cold solder joint.
(2) flip-flop has inputs, one of the side of the trigger pulse signal oscilloscope screen should change the input signal polarity, then the other side of the flip-flops are pulsed signals. Trigger pulse number and amplitude of the two groups should be basically the same. Otherwise, the following situations.
① no input signal (pre-magnetic amplifier in the normal working state), output a trigger pulse, may be:
A, a trigger pulse output side of the transistor is damaged, or c, e very cold solder joint.
B, resistors R204, R205, R208, R209 resistance have changed.
② an input signal, no output trigger pulse, may be:
A, no output pulse at the side of the transistor, UJT damage.
B, no output pulse at the side of the pulse transformer primary or secondary open circuit or short circuit.
C, no output pulse at the side of the diode (D207 or D208) short-circuit.
③ the output trigger pulse is not normal and the following phenomena:
A, no signal sets flip-flop has a pulse output, plus all the normal after the signal may be fake solder electrolytic capacitor C202 or C203.
B, both sides began to flip-flop outputs are normal, working for some time, the output pulse gradually disappeared, it may UJT problems.
C, the output appears positive and negative pulses, may be diodes D207, D208 has been breakdown or cold solder joint.
(3) After the above inspection and maintenance, trouble-free in the case of the control loop servo amplifier should be able to work properly. Otherwise, the following two situations:
① no input signal, there is the output voltage (voltage close to 220VAC) you may be:
A, thyristor SCR1, SCR2 damage.
B, capacitor C301, C302 is the breakdown.
② an input signal, no output signal or output voltage is low, it may be:
A, diode D301 ~ D308 has been breakdown.
B, thyristor SCR1, SCR2 damage.
2.2 Control Valve
4 ~ 20mA input signal, regulating valve stem can be rated as the signal changes within the travel, the next move freely. If they can not function normally, you may have the following breakdown:
① manipulator wheel paresthesia
A, felt too light and may be hand-sold off or broken wheel card.
B, feeling too much, or spin unchanged. There are foreign bodies Casey reducer; spool and liner, or stuck with the valve seat; stem a serious bent.
② Input 4 ~ 20mA signal, control valve does not move.
A, the system wiring is incorrect.
B, motor phase capacitor CD is damaged.
C, electrical wiring open.
D, spool or the valve stem is broken off (the executing agency take any action at this time)
③ Input 4 ~ 20mA signal, regulating valve rated to go endless journey.
A, differential transformer position is not a good tune.
B, diode D701 ~ D712 in the individual damaged.
C, transistor BG701 damage.
(4) on-site use of other failures.
① valve shocks, tweet.
A, sensitivity adjusted too high, the executive body oscillation.
B, too much fluid pressure changes, the implementing agency under thrust.
C, control valve selection big, valves often work in a small opening.
D, medium flow direction and valve closure in the same direction.
E, near the other focal impact, support unstable.
F, spool and bushing wear serious.
② valve moves slow.
A, medium viscosity too big, there are blockages or coking phenomena.
B, packing aging, packing presses too tight.
③ large amount of leakage.
A, spool or the valve seat is corrosion, wear and tear.
B, valve seat loose or corroded threads.
C, valve seat, a foreign body on the spool.
D, a starting point for the valve (electrical open) or endpoint (electric closed) did not transfer well.
④ filler and the upper and lower junction leakage valve cover.
A, packing gland did not compress.
B, PTFE packing aging deterioration.
C, stem damage.
D, fastening nut loose.
E, damage gaskets.
Electric control valve the proper use and maintenance, not only can improve the reliability of process control can also increase the service life of electric control valves, the energy consumption of enterprises have considerable economic benefits.
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