Pneumatic valve maintenance Jinzhou Liuguo Yang Mao Mao six pneumatic valve is one of the widely used petrochemical enterprises. It is accurate and normal work to ensure the normal operation of process equipment and safety is of great significance. Therefore, to strengthen the maintenance of pneumatic control valve is necessary. First, check the focus of the inspection site when the body wall: In the high pressure and corrosive media occasions, the valve body wall, diaphragm valve diaphragm often subject to media impact and corrosion, we must focus on inspection of pressure decay; Check Valve seat: medium infiltration due to work, the fixed valve seat thread inner surface vulnerable to corrosion and make the valve seat loose; check the valve: the valve spool is one of the movable parts of the regulating valve, the erosion of the media is more serious, Maintenance should carefully check the various parts of the valve core is corroded, worn, especially in the case of high pressure, valve core wear due to cavitation caused cavitation is more serious. Check the sealing packing: Check the packing asbestos rope is dry, such as the use of PTFE packing, should be checked to see if aging and its mating surface is damaged; Check the actuator in the aging of the rubber film , Whether there is cracking phenomenon. Second, the pneumatic control valve with the routine maintenance When the control valve graphite asbestos as a filler, about three months should be added to the filler on a lubricant to ensure flexible and easy to use control valve. If it is found that the packing pressure cap is very low, it should be filled with filler. If it is found that the PTFE packing is hardened, it should be promptly replaced. Attention should be paid to the operation of the regulating valve in the circuit inspection. Check the valve position indicator and the regulator The output is consistent with; regulator valve positioner should always check the gas source and found the problem promptly handled; should always maintain the health of the valve and the complete and easy-to-use components. Third, the common faults and causes (a) control valve does not move. Symptoms and causes are as follows: 1. No signal, no air source. ①gas source is not open, ② due to gas source water in the winter icing, resulting in duct blockage or filter, pressure regulator plug failure, ③ compressor failure; ④ gas mains leakage. 2. A gas source, no signal. ①regulator failure, ② signal tube leakage; ③ bellows leak locator; ④ regulate the omentum damage. 3. Locator airless. ①filter blockage; ② valve failure I ③ pipeline leakage or blockage. 4. Locator gas source, no output. The throttle of the positioner is blocked. 5. A signal, no action. ①spool off, ② valve core and the community or with the seat stuck; ③ stem bent or broken; ④ seat valve core block or block of dirt; ⑤ actuator spring rust due to long-term useless. (B) control valve instability. Symptoms and causes are as follows: 1. Gas pressure instability. ①compressor capacity is too small; ② valve failure. 2. Signal pressure is not stable. ①The time constant of the control system (T = RC) is not appropriate; ② The regulator output is not stable. 3. Gas pressure is stable, the signal pressure is stable, but the control valve action is still unstable. ①locator amplifier ball valve dirt worn lax, especially when the air consumption will produce output shock; ② locator amplifier nozzle baffle is not parallel, the baffle cover nozzle; ③ output tube , Line air leakage; ④ actuator stiffness is too small; ⑤ stem friction in the movement of large, with the contact parts of the block phenomenon. (C) regulating valve vibration. Symptoms and causes are as follows: 1. The regulating valve vibrates at any opening. ①unsteady support; ② nearby vibration source; ③ valve core and bush wear serious. 2. Valve close to the fully closed position when the vibration. ①control valve selected, often used in a small opening; ② single-seat valve medium flow direction and closed the opposite direction. (D) regulating valve slow action. The phenomenon of dullness and the reasons are as follows: 1. Stem only in unilateral action slow. ①Pneumatic diaphragm actuator diaphragm rupture leakage; ② "O" -type seal leakage in the actuator. 2. Stem in the reciprocating action are slow phenomenon. ①blockage of viscous substances in the valve body; ② polytetrafluoroethylene filler hardening or graphite asbestos filler lubricant drying; ③ packing plus too tight, frictional resistance increases; ④ stem because the valve does not lead to direct friction resistance; ⑤ no Pneumatic positioner valve will lead to slow action. (E) the amount of leakage control valve increases. The reasons for the leakage are as follows: 1. Leakage when the valve is closed. ①spool is worn, serious leakage, ② valve not adjusted off is not strict. 2. Valve can not reach the fully closed position. ①medium pressure is too large, the actuator rigidity is small, the valve is not strict; ② valve foreign body; ③ bushing sintering. (F) adjustable flow rate smaller. The main reason is that the valve core is corroded and smaller, so that the adjustable minimum flow rate becomes larger. Understand the phenomenon of pneumatic control valve failure and the reasons that symptomatic measures can be taken to resolve.
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