(1) The valve does not operate.
The fault phenomenon and its causes are as follows:
1. No source of gas.① The air source is not open, ② due to the water content of the air source ice in winter, resulting in the air duct blockage or the filter, pressure relief valve blockage failure, ③ air compressor failure, ④ air source main pipe leakage.
2. Air source, no signal.① DCS output fault, ② signal cable interruption; ③ locator fault;
3. The locator has no gas source.① Filter blockage; ② pressure relief valve failure ③ pipe leakage or blockage.
4. The positioner has a gas source and no output. The nozzle is blocked.
5. Signal, no action.① Core and seat stuck, ② stem bent or broken; ③ seat core frozen or coke block dirt; ④ actuator spring rust due to long use; ⑤ valve spring broken or diaphragm damaged; ⑥ solenoid valve failure; ⑦ stem stuck.
(2) The operation of the valve is unstable.
The fault phenomenon and causes are as follows:
1. Unstable pressure of the air source. Pressure relief valve failure.
2. The signal pressure is unstable.① PID parameters of control point; ② regulator output is unstable; ③ wiring is loose.
3. The air source pressure is stable, and the signal pressure is also stable, but the action of the regulating valve is still unstable.① Locator fault; ② output pipe and line leak; ③ actuator is too rigid; large friction resistance in ④ stem movement; ⑤ working condition is unstable, the current condition does not match the selection; ⑥ diaphragm or spring is broken; ⑦ cylinder or membrane head is leaking; ⑧ valve interior is damaged; ⑨ measuring point is unstable.
(3) Valve vibration.
The fault phenomenon and causes are as follows:
1. The regulating valve vibrates at any opening degree.① Unstable support; vibration source near ②; ③ spool and bushing; severe throttling.
2. The regulating valve vibrates near the full closed position.① The regulating valve is large and often used under small opening; ② single seat valve is not suitable for working conditions.
(4) The action of the valve is slow.
The phenomenon and causes of dullness are as follows:
The valve stem is dull during the reciprocating action.① Bond blockage in the valve; ② PTFE packing deterioration hardening or graphite packing lubricating oil dry; ③ packing is too tight, the friction resistance increases; ④ large friction resistance due to the valve stem is not straight; ⑤ cylinder strength is not large enough, cylinder or gas source problems; ⑥ operating condition changes; ⑦ spring fault; ⑧ locator failure.
(5) The leakage amount of the valve increases.
The causes of the leakage are as follows:
1. Large leakage volume when the valve is fully closed.① The valve core is worn, internal leakage is serious, ② valve is not adjusted and closed; ③ mechanical zero is not adjusted.
2. The valve cannot reach the fully closed position.① The medium pressure difference is too large, the actuator torque is too small, the air source pressure is not enough, and the valve is not closed; there are foreign objects in ② valve; the ③ bushing is coking; the interior of ④ valve is damaged.
(6) The flow adjustable range is smaller.
material cause: The valve core or valve seat is corroded smaller, so that the normal opening becomes larger.
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Post time: Sep-23-2023