Routine maintenance of pneumatic conditioning valves
When the conditioning valve is packed with graphite-asbestos, lubricating oil should be added to the packing once in about three months to ensure that the conditioning valve is flexible and easy to use. If it is found that the pressure cap of the packing is very low, the packing should be compensated, and if the PTFE dry packing is found to be hardened, it should be replaced in time; Attention should be paid to the operation status of the conditioning valve during the patrol inspection, and check whether the valve position indicator and the output of the regulator are consistent; For the conditioning valve with a positioner, the air source should be checked frequently, and the problem should be dealt with in time; The hygiene of the conditioning valve and the integrity of the components should be maintained at all times.
Common problems and the reasons for their occurrence
(1) The conditioning valve does not operate. The symptoms and causes are as follows:
1. No signal, no air source. (1) The air source is not opened, (2) because the water contained in the air source freezes in winter, resulting in the blockage of the air duct or the blockage of the filter and pressure reducing valve, (3) the compressor is faulty; (4) Leakage of air source main pipe.
2. There is a gas source, no signal. (1) Conditioner fault, (2) Signal tube leakage; (3) Air leakage of the bellows of the positioner; (4) Conditioning omentum diaphragm damage.
3. The positioner has no air source. (1) Filter blockage; (2) Pressure reducing valve fault I (3) pipeline leakage or blockage.
4. The positioner has an air source, no output. Positioner saves hole blockage.
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 twisted or broken; (4) Frozen or scorched dirt on the seat and spool; (5) The actuator spring is rusted due to long-term use.
(2) The action of the conditioning valve is unstable. The symptoms and causes are as follows:
1. The pressure of the air source is unstable. (1) The compressor capacity is too small; (2) Faulty pressure reducing valve.
2. The signal pressure is unstable. (1) The time constant (T=RC) of the control system is inappropriate; (2) The output of the conditioner is not stable.
3. The air source pressure is stable, and the signal pressure is also stable, but the action of the conditioning valve is still unstable. (1) The ball valve of the amplifier in the positioner is not tightly closed by dirt wear, and the output oscillation will occur when the air consumption is particularly increased; (2) The nozzle baffle of the amplifier in the positioner is not parallel, and the baffle cannot cover the nozzle; (3) Air leakage from output pipe and line; (4) The rigidity of the actuator is too small; (5) The friction resistance is large in the movement of the valve stem, and there is a blockage phenomenon with the contact part.
(3) Conditioning valve oscillation. The symptoms and causes are as follows:
1. The conditioning valve oscillates at any opening. (1) Unstable support; (2) there is an oscillation source nearby; (3) The spool and bushing are severely worn.
2. The conditioning valve oscillates when it is close to the fully closed position. (1) The conditioning valve is selected to be large, and it is often used under a small opening; (2) The medium flow direction of the single-seat valve is opposite to the closing direction.
(4) The action of the conditioning valve is dull. The phenomenon of dullness and its causes are as follows:
1. The stem is dull only when acting in one direction. (1) The diaphragm is damaged and leaked in the pneumatic film actuator; (2) The "O" type seal leaks in the actuator.
2. The valve stem has a dull phenomenon when it reciprocates. (1) There is sticky blockage in the valve body; (2) PTFE filler deteriorates and hardens or graphite-asbestos filler lubricating oil is dry; (3) The filler is added too tightly, and the friction resistance increases; (4) Because the stem is not straight, the friction resistance is large; (5) Pneumatic conditioning valves without positioners will also lead to dull action.
(5) The leakage of the conditioning valve increases. The reasons for the leak are as follows:
1. When the valve is fully closed, the leakage is large. (1) The valve core is worn, and the internal leakage is severe, (2) The valve is not adjusted and closed tightly.
2. The valve cannot reach the fully closed position. (1) The pressure difference of the medium is too large, the rigidity of the actuator is small, and the valve is not tightly closed; (2) There are foreign bodies in the valve; (3) Bushing sintering.
(6) The scale of the flow can be adjusted and reduced. The main reason is that the spool is corroded and becomes smaller, which makes the adjustable* small flow rate larger.
Understand the problem phenomenon and cause of pneumatic conditioning valve, and take measures to solve the problem.
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