Pneumatic control valve maintenance

Pneumatic control valve is widely used in petroleum chemical industry is one of the instrument. It is precisely to work properly in ensuring the normal operation of process plants and production safety have an important significance. Therefore, strengthening the pneumatic valve repair is necessary.

     First, repair parts, when the focus of inspection

     Check between the body wall: In high-pressure differential and corrosive media of the occasion, body wall, diaphragm of the diaphragm often media impact and corrosion, we must focus on examination of pressure decay;

     Check Seat: Due to the work of media penetration, fixed seat screw used in the inner surface susceptible to corrosion Ershi seat relaxation;

     Check spool: spool valve to regulate one of movable parts, subject to more severe erosion of the medium, repair should be careful when you check the valve core ministries is corrosion, wear and tear, especially in the case of high-pressure differential, spool of wear due to cavitation caused by cavitation phenomenon is even more serious. Were seriously damaged valve core should be replaced; check Filler: Check the packing asbestos rope is dry, such as the use of PTFE packing, should pay attention to check whether the aging and its mating surface is damaged;

     Check the executive body of the rubber membrane is aging, whether the cracking phenomenon.

     2, pneumatic control valve with daily maintenance

     When the control valve using graphite asbestos as a filler, the filler should be about three months to add a lubricant to ensure the control valve and flexible easy to use. Found filling pressure cap low, should be added fillers, such as found in the dry filler PTFE B sclerosis, should be promptly replaced; should pay attention to inspection tour of the operation of control valve, check valve position indicator and regulator the output is consistent; to have locator control valve should always check the gas source, identify problems and timely treatment; should always maintain a control valve components of health as well as a complete easy to use.

     3, common faults and their causes

     (A) the control valve does not move. Phenomenon and the reasons for failure are as follows:

     1. No signal, no gas source. ① gas source is not open, ② gas supply due to water freezing in the winter, leading to blocked ducts or filters, valve block failure, ③ compressor failure; ④ source of mains gas leak.

     2. There is gas source, no signal. ① regulator failure, ② the signal tube leakage; ③ bellows leak locator; ④ regulate film damaged retina.

     3. No gas source locator. ① filter plugging; ② valve failure I ③ pipeline leak or blockage.

     4. Positioning device has gas supply, no output. Locator orifice plug.

     5. There is signal, no action. Spool off ①, ② spool with the social or stuck with the valve seat; ③ stem bending or breakage; ④ spool seat block of frozen or coke dirt; ⑤ implementing agencies do not have the spring due to the long-term rust die.

     (B) the control valve moves instability. Phenomenon and the reasons for failure are as follows:

     1. Pressure gas source of instability. ① compressor capacity is too small; ② valve failure.

     2. The signal pressure instability. ① control system time constant (T = RC) inappropriate; ② regulator output instability.

     3. A stable gas supply pressure, the signal pressure is stable, but still stable valve action. ① Locator amplifier ball wear off by the dirt loose, especially with increasing gas consumption will produce the output shock; ② Locator amplifier nozzle baffle is not parallel to baffle nozzle cover not live; ③ Output Pipe, line leak; ④ executive body rigidity is too small; ⑤ stem movement friction large parts of a block in contact with the phenomenon.

     (C) regulating valve vibration. Phenomenon and the reasons for failure are as follows:

     1. Regulating valve opening at any vibration at all times. ① supporting instability; ② near the source of vibration; ③ spool and bushing wear serious.

     2. Regulating valve near the fully closed position vibration. ① big selection valve, often used in small openings; ② single-seat valve media flow on and off in the opposite direction.

     (D) regulating valve movements slow. Slow phenomenon, and the following reasons:

     1. Stem only in one direction when the slow movement. ① pneumatic membrane leakage of the implementing agencies in the membrane damage; ② implementing agencies in the "O" type seal leakage.

     2. When the stem at reciprocating movements are slow phenomenon. ① valve body with sticky material to plug; ② sclerosis or graphite PTFE packing deterioration of asbestos packing a dry lubricant; ③ packing too tightly increases, friction increases; ④ stem not directly lead to friction due to large; ⑤ No The pneumatic control valve positioner can lead to slow movement.

     (E) increase the amount of valve leakage. Leakage of the following reasons:

     1. Valve fully closed when the leakage of large quantities. ① spool is worn to a serious internal leakage, ② strictly off valve is not a good tune.

     2. Valve fail to fully closed position. ① medium pressure too great, the executing agency rigidity is small, loose valve closed; ② of a foreign body within the valve; ③ sintered bushing.

     (F) adjustable flow range becomes smaller. The main reason is corrosion smaller spool, so that the minimum flow rate adjustable larger.

     Pneumatic control valve failure to understand the phenomenon and the reasons to be symptomatic to take measures to resolve it. 

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