Pneumatic valve failure phenomenon and the reasons
Valve graphite asbestos as a filler, the filler should be about three months to add a lubricant to ensure a flexible easy to use control valve. Found filling pressure cap low, should be added fillers, such as found in the dry filler PTFE B sclerosis, should be promptly replaced; should pay attention to the inspection tour of the operation of control valve, check valve position indicator and regulator output is consistent; on a positioner control valve should always check the gas source, identify problems and timely treatment; control valve should be kept sanitary and easy to use all parts complete.
Common Faults and pneumatic control valve causes a control valve does not move, movement control valve instability, vibration control valve, control valve moves slowly, increasing control valve leakage, flow, and small adjustable limit.
A) regulating the valve does not work. Phenomenon and the reasons for failure are as follows:
1. No signal, no gas supply. ① gas source is not open, ② gas source water as ice in the winter, leading to blocked ducts or filters, valve block failure, ③ compressor failure; ④ gas supply mains leak.
2. A gas source, no signal. ① regulator fault, ② signal pipe leak; ③ bellows leak locator; ④ regulation retina become damaged.
3. Locator No gas source. ① filter plug; ② valve failure; ③ pipeline leakage or blockage.
4. Locator with gas source, no output. Locator orifice plug.
5. A signal, no action. Spool off ①, ② stuck valve or valve seat; ③ bent or broken valve stem; ④ spool seat block frozen or coke dirt; ⑤ implementing agencies do not have the rust spring due to the long dead.
B) the action control valve instability. Failure phenomenon and the reasons are as follows:
1. Air pressure instability. ① compressor capacity is too small; ② valve failure.
2. Signal pressure instability. ① control system time constant (T = RC) inappropriate; ② regulator output instability.
3. Air pressure stability, the signal pressure are stable, but still not stable valve action. ① locator ball in the amplifier off by the loose dirt and wear, increase gas consumption in particular will produce an output shock; ② nozzle locator in the amplifier is not parallel to the baffle, baffle cover any of nozzle; ③ Output tube, line leak; ④ executive body rigidity is too small; ⑤ stem movement friction large parts of a block in contact with the phenomenon.
3) regulating valve vibration. Failure phenomenon and the reasons are as follows:
1. Valve opening degrees are any vibration. ① propping; ② near the vibration source; ③ serious spool and bushing wear.
2. Valve near the fully closed position, vibration. ① big selection valve, often used in small openings; ② single-medium flow and close the valve seat in the opposite direction.
D) the control valve moves slow. Slow phenomenon and for the following reasons:
1. Stem only when the slow movement in one direction. ① membrane pneumatic membrane actuator in the leak damaged; ② implementing agencies in the "O" type seal leakage.
2. Stem were slow in reciprocating action when the phenomenon. ① plug valve body, viscous material; ② hardening or graphite PTFE packing deterioration of asbestos packing a drying oil; ③ packed too tightly increases, friction increases; ④ friction because the valve stem does not always lead to large; ⑤ no pneumatic control valve positioner can lead to slow movement.
E) regulating valve leakage increases. Leakage of the following reasons:
1. Valve is fully closed when the leak volume. ① spool is worn, severe internal leakage, ② off valve is not adjusted the loose.
2. Valve fail to fully closed position. ① medium pressure too small executive body rigid, strictly off valve; ② a foreign body within the valve; ③ sintered bushing.
F) adjustable flow range becomes smaller. Mainly due to corrosion of smaller spool, so that the minimum flow rate adjustable bigger.
Failure to understand the phenomenon of pneumatic control valves and the reasons, you can take measures to resolve symptomatic.