When the pneumatic single-seat control valve graphite asbestos 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 during the inspection, check the position indicator and the regulator The output is consistent; on the positioner pneumatic single-seat control valve should always check the gas source and found that problems in a timely manner; should always maintain the pneumatic single-seat control valve and the health of all components and easy to use. Pneumatic single seat regulating valve common failures and causes (A) Pneumatic single seat regulating valve does not move. Symptoms and causes are as follows: 1. No signal, no air source. ①gas source is not open; ② due to air source water in winter icing, resulting in duct blockage or filter, pressure regulator plug failure; ③ compressor failure; ④ air mains leakage. 2. Air source, no signal. ①regulator failure; ② signal tube leakage; ③ bellows leak locator; ④ regulatory mesh membrane damage. 3. Locator no air source. ①clogged filter; ② valve failure; ③ pipeline leakage or blockage. 4. Locator has a gas source, no output. The throttle of the positioner is blocked. 5. There is a signal, no action. (1) the spool off; (2) the spool and the social or seat stuck; (3) the valve stem bent or broken; (4) the valve seat block frozen or coke dirt; (B) pneumatic single-seat control valve instability. Symptoms and causes are as follows: 1. Air 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 stability, signal pressure is stable, but the control valve action is still unstable. ①locator amplifier ball valve dirt worn lax, air consumption will increase when the output shock will produce; 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) single-seat pneumatic 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. Regulating valve in the fully closed position near the vibration. ①control valve selected, often used in a small opening; ② single-seat valve medium flow direction and closed the opposite direction. (D) Pneumatic single-seat control valve slow action. The phenomenon of dullness and the reasons are as follows: 1. The stem is only dull when moving in one direction. 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) Pneumatic single seat control valve leakage increases. The reasons for the leakage are as follows: 1. The valve leaks when the valve is fully closed. ①spool is worn, serious leakage, ② valve not adjusted off is not strict. 2. The valve does 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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