Common faults and causes of pneumatic control valve

Time：

Dec 08,2022

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(1) The regulating valve does not act, and the fault phenomena and causes are as follows:

1. The regulating valve does not act, and the fault phenomena and causes are as follows:

2. There is air source but no signal. 1 regulator failure 2 positioner corrugated steel air leakage 3 regulator diaphragm damage

3. The positioner has no air source, 1 filter is blocked, 2 pressure reducing valve is faulty, 3 pipeline is leaked or blocked

4. The positioner has air source and no output. The orifice of the positioner is blocked

5. There is signal but no action. 1. The valve core falls off, 2. The valve core is stuck with the society or the valve seat, 3. The valve rod is bent or broken, 4. The valve core of the valve seat is frozen or coke dirt. 5. The actuator spring is repaired because it is not used for a long time

(2) The action of the regulating valve is unstable. The fault phenomena and causes are as follows:

1. The air supply pressure is unstable # 1 the compressor capacity is too small # 2 the pressure reducing valve fails

2. The signal pressure is unstable. 1. The time constant of the control system is inappropriate. 2. The regulator output is unstable

3. The air source pressure and signal pressure are stable, but the action of the regulating valve is unstable. 1. The ball valve of the amplifier in the positioner is not worn tightly by stolen goods, and the output oscillation will occur when the air consumption increases. 2 the nozzle baffle of the amplifier in the positioner is not parallel, the baffle cannot cover the nozzle, and 3 the output pipe and line leak. 4. The rigidity of the actuator is too small. 5. The friction resistance of the valve rod is large during the movement, and there is blocking at the contact part.

(3) The regulating valve vibrates. The fault phenomena and causes are as follows:

1. The regulating valve vibrates at any opening. 1. Unstable support 2. There is a vibration source near 3. The valve core and bushing are seriously worn.

2. When the regulating valve is in the fully closed position, it vibrates. 1. The regulating valve is selected to be large and is often used under small opening: 2. The medium flow direction of single seat valve is opposite to the closing direction

(4) The phenomenon and causes of slow action of regulating valve are as follows:

1. The valve stem is only slow in one direction. 1. The diaphragm in the pneumatic diaphragm actuator is damaged and leaked. 2. The "O" seal in the actuator is leaked

2. The valve stem is dull during reciprocating action 1 There is a sticky blockage in the valve body. 2 Teflon packing is deteriorated and hardened or graphite asbestos packing lubricating oil is dry 3. If the packing is too tight, the friction resistance increases. 4. The friction resistance is large because the valve stem is not straight. 5 pneumatic control valve without positioner will also lead to retardation

(5) The leakage of the regulating valve increases, and the reasons for the leakage are as follows:

1. When the valve is fully closed, the leakage is large, 1 The valve core is worn, the internal leakage is serious, and the 2 valve is not adjusted and closed tightly

2. The valve cannot reach the fully closed position 1 The medium pressure difference is too large, the rigidity of the actuator is small, and the valve is not tightly closed 2 There are foreign matters in the valve 3 and the bushing is sintered

(6) The adjustable flow range becomes smaller. The main reason is that the valve core is corroded and smaller, so that the adjustable minimum flow becomes larger.

Understand the fault phenomenon and causes of pneumatic control valve, and take measures to solve the symptoms.

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