Common faults and their causes: (1) The regulating valve does not act. The fault phenomenon and reasons are as follows: 1. No signal, no air source. ①The air source is not turned on, ②The air duct is blocked or the filter and pressure reducing valve are blocked due to the water in the air source freezing in winter, ③The compressor is faulty; ④The air source main pipe leaks. 2. With air source, no signal. ①The regulator is faulty, ②the signal pipe leaks; ③the positioner bellows leaks air; ④the adjusting mesh diaphragm is damaged. 3. The positioner has no air supply. ①The filter is blocked; ②The pressure reducing valve is faulty. I③The pipeline is leaking or blocked. 4. The positioner has air source and no output. The orifice of the positioner is clogged. 5. There is a signal, no action. ① The valve core falls off, ② the valve core is stuck with the society or with the valve seat; ③ The valve stem is bent or broken; ④ The valve seat valve core is frozen or coke dirt; (2) The action of the regulating valve is unstable. The fault phenomenon and reasons are as follows: 1. Air supply pressure is unstable. ①The compressor capacity is too small; ②The pressure reducing valve is faulty. 2. Signal pressure is unstable. ①The time constant of the control system (T=RC) is not appropriate; ②The output of the regulator is unstable. 3. The air source pressure is stable and the signal pressure is also stable, but the action of the regulating valve is still unstable. ①The ball valve
of the amplifier in the positioner is not tightly closed due to the wear and tear of dirt, and the output shock will occur when the air consumption is particularly increased; ②The nozzle baffle of the amplifier in the positioner is not parallel, and the baffle cannot cover the nozzle; ③The output pipe , Air leakage from the line; ④The rigidity of the actuator is too small; (3) Vibration of the regulating valve. The fault phenomenon and reasons are as follows: 1. The regulating valve vibrates at any opening. ①The support is unstable; ②There is a vibration source nearby; ③The valve core and bushing are seriously worn. 2. The regulator valve vibrates near the fully closed position. ①The control valve is selected to be large, and it is often used at a small opening; ②The medium flow direction of the single-seat valve is opposite to the closing direction. (4) The action of the regulating valve is slow. The phenomenon and reasons of sluggishness are as follows: 1. The stem is sluggish only in one direction. ①The diaphragm is damaged and leaked in the pneumatic diaphragm actuator; ②The 'O' type seal leaks in the actuator. 2. The valve stem is sluggish during the reciprocating action. ①The valve body is clogged with sticky substances; ②The PTFE packing is deteriorated and hardened or the graphite-asbestos packing lubricating oil is dry; ③The packing is too tight, and the frictional resistance increases; ④The frictional resistance is large because the valve stem is not straight; The positioner's pneumatic control valve can also cause sluggish action. (5) The leakage of the regulating valve increases. The reasons for the leakage are as follows: 1. The leakage is large when the valve is fully closed. ①The valve core is worn, and the internal leakage is serious. ②The valve is not properly adjusted and the valve is not closed tightly. 2. The valve does not reach the fully closed position. ①The pressure difference of the medium is too large, the rigidity of the actuator is small, and the valve is not closed tightly; ②There is foreign matter in the valve; ③The bushing is sintered. (6) The adjustable range of flow rate becomes smaller. The main reason is that the spool is corroded and becomes smaller, thereby making the adjustable minimum flow larger.
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