(1) Diaphragm head type actuator

1. The liquid level control valve is out of control and cannot be opened.

The liquid level measurement indication is already very high, and the regulator output is also very large, but the regulating valve cannot be opened, so the mechanical handwheel control is required. Check the valve positioner (remove the diaphragm head connecting pipe and plug it), press the nozzle baffle mechanism, there is no output change of the positioner, check that the throttle hole is unobstructed, disassemble the amplifier and find that the amplifier diaphragm is broken. Replace the diaphragm and put the regulating valve back into automatic control. The diaphragm of the valve positioner amplifier is broken, there is no back pressure in the back pressure chamber, and the amplifier has no output, so the regulating valve is out of control.

2. The valve positioner feedback slide rod is rusty

The liquid level fluctuated severely. The inspection found that the slide rod of the feedback mechanism of the valve positioner was completely rusted and could not rotate, so it had to be controlled by hand wheel. Try to knock out the slide rod, remove the rust and add oil before reinstalling it, and the regulating valve returns to normal. The valve positioner feedback mechanism adds the corresponding feedback amount of the positioner as the valve opening changes. If the sliding rod is rusted, the feedback force cannot change with the opening of the valve, and the valve opening cannot stop at the corresponding position of the regulator output signal, causing the liquid level to fluctuate.

3. The pressure control valve cannot operate

The natural gas volume cannot be reduced after the primary process load reduction is due to the inability of the natural gas pressure regulating valve to operate. During the inspection, it was found that the output signal of the valve was normal. It was estimated that the valve core was carbonized and stuck. After increasing the pneumatic signal and adding the handwheel force, the valve was closed. After stopping the valve, the valve was disassembled and inspected. As expected, because the valve usually has few load stabilizing switches, the carbon black contained in the natural gas formed carbon and stuck in the small gap between the valve stem and the guide sleeve. Therefore, this valve will be disassembled and cleaned during annual overhaul to avoid similar accidents. Today’s focus:

4. Valve core breaks out of control

The liquid level in the absorption tower cannot be controlled, and the recorded curve fluctuates and decreases. Check that there are no problems with the transmitter and regulator. When using the handwheel control, I found that the handwheel was not as heavy and light as usual when pressed or lifted. It was judged that the valve core was broken, so I was forced to stop and disassemble the regulating valve. It was found that the connection between the valve core and the valve stem was disconnected. We had to replace the valve core and surfacing the valve core and valve stem connection with a circle to increase the strength to avoid similar accidents. The valve core fracture is caused by the unbalanced force under the medium pressure.

5. The multi-regulating valve cannot be opened due to packing.

When driving after a major overhaul, the liquid level of the liquid ammonia flash tank was high. On-site inspection found that the regulating valve was not open. He hurriedly turned on the handwheel control to make the liquid level normal. The instrument engineer found that the regulating valve was being inspected for fear of leaking liquid ammonia, and the packing was added. Too much, too tight pressure, high friction. Appropriately loosen the roots and compress the boil to allow it to move flexibly and re-throw with self-control.

6. Flow control fluctuations

The anti-surge flow control vent valve of the air compressor frequently switches on and off during driving, resulting in unstable flow. Check that there is no problem with the regulator and regulating valve, but the opening of the regulating valve is always very small. When the air flow rate increases, the regulator outputs a signal up to 1 MPa/cm 2 to the regulating valve (air shut-off valve), which is similar to the integral saturation phenomenon. When the positioner receives a signal to open the valve, the positioner has to go through a dead zone before it can take control. This dead zone makes the regulator output smaller, and when the regulating valve is activated, it goes too far. This repeated process, combined with The low-end control linearity of the regulating valve is poor, so the valve must switch frequently, making the flow control unstable. The only solution is to suggest that the process increase the compressor speed, increase the venting volume, and disengage the low-end control of the regulating valve.

7. Absorption tower liquid level low alarm

Check that the regulating valve is fully closed, so we have to cooperate with the process to return to valve B operation. Disassemble the valve and check that the valve core is severely damaged due to erosion. Replace with a new valve core and install and calibrate it for later use. The valve core is eroded and has no control function. If not handled in time, the liquid level will be lower than the interlocking liquid level, which will cause shutdown.

8. The regulating valve stem is bent and cannot be opened.

After the overhaul, the liquid level control valve of the absorption tower could not be opened when driving. The inspection found that the valve stem was bent during maintenance, so the valve stem had to be disassembled, removed, straightened, reinstalled, and put into operation. Be careful when inspecting and repairing the regulating valve. Especially for valves with a non-plywood connection structure, the diaphragm head is heavy, and you need to turn the diaphragm head several turns of the turnbuckle. If you are not careful, you may bend the valve stem. In addition, after the regulating valve is inspected, installed and calibrated, it should be turned on and off several times to make sure that its action is very flexible before stopping.

9. The regulating valve cannot operate

During the start-up process after the maintenance, it was found that the liquid level control valve of the absorption tower could not operate, so the company was forced to stop and open the regulating valve to check. It was found that the iron filings that fell in between the guide sleeve and the valve stem were stuck. During the maintenance of this valve, the lower flange was pressed with a lathe to remove the old guide sleeve and replaced with a new guide sleeve. When assembling the valve, the cleaning was not careful. There were iron filings falling under the guide sleeve. When checking the valve, The iron filings below did not hinder the movement of the valve and no problem was found. After the medium is driven in, the medium rushes into the guide sleeve from the balance hole, and flows out of the balance hole through the guide sleeve. The iron filings roll back and forth in the guide sleeve, and are stuck between the valve stem and the guide sleeve, and the valve cannot operate. .

10. The regulating valve cannot be opened

During the driving process, the carbon dioxide pressure regulating valve could not be opened, the pressure was forced high, and the vent valve was opened. When checking the cause, it was found that the latch controlled by the mechanical hand wheel had not been pulled out, and the regulating valve was in the mechanical manual closing position, and of course it could not be opened. Adjust the regulator output signal to zero, remove the latch, and put the regulating valve into operation.

11. Friction was found in the regulating valve

After maintenance of the natural gas pressure control valve, it was found that the friction was not good, causing pressure fluctuations. The reason for friction is that the friction phenomenon is eliminated after the flange is covered during maintenance and assembly.

Generally, the gap between the valve stem and the guide sleeve of the regulating valve is very small. The gland flange must be flattened during assembly, otherwise it will either leak or the valve stem and the guide sleeve are not concentric and cause friction.

12. The regulating valve is suddenly fully closed causing parking.

The natural gas flow regulating valve suddenly closed completely, the natural gas flow dropped to zero, and the entire system was forced to shut down. Check that the regulator has output, but the regulating valve is fully closed, turn on the hand wheel, and resume production in accordance with the process. Remove the output air duct of the positioner, plug it with your hands, push the nozzle baffle mechanism, the output signal can reach 1MPa/cm 2 , indicating that the problem lies in the regulating valve, send the air signal to the membrane head, and there is gas in the vent hole of the membrane head Released, proving that the diaphragm is broken. Replace the diaphragm regulating valve and put it into operation.

13. Casting automatically causes system disturbance

The steam flow regulating valve is controlled by a handwheel at the first stage. After checking the positioner, it will restart automatically. When the handwheel is released, it will cause system disturbance. The reason is that the output signal of the regulator remains at the value before the handwheel is turned on. The operator quickly releases the handwheel without looking at the positioner output, and the regulating valve opens accordingly. Because the diaphragm head is too large, there is an inflation lag process, causing the air shut-off valve to suddenly open much wider, causing a disturbance to the system.

14. Dealing with gas source leakage problems

When dealing with air leakage from the air source joint of the valve positioner, the joint slipped due to excessive force, the air source pipe was washed away, and the regulating valve immediately started to operate. The instrument worker immediately inserted the air source pipe back, pressed it tightly with his hand, and restored the original position of the regulating valve. Then he cooperated with the operator to turn the regulating valve on the hand wheel and replace the joint. This emergency measure is also very effective in emergency situations.

15. The diaphragm valve cannot be opened

The water treatment regeneration discharge valve could not be opened. After disassembly and inspection, it was found that the diaphragm was torn. After replacing the new diaphragm, it could not be opened again within a few days, and the above situation happened again. It was analyzed that the cause of the diaphragm damage was that the diaphragm valve diaphragm head limit bolt was loose, the limit position changed, the valve stem stroke was too large, and the pulling force exceeded the elastic range of the diaphragm, so the diaphragm was damaged. Readjust the limit bolt, replace the diaphragm, and the diaphragm valve returns to normal.

(2) Cylinder actuator

  1. The hydraulic regulating valve cannot be closed

During the driving process, the steam pressure regulating valve opened automatically and could not be closed even by adding a signal. The inspection revealed that the faulty throttle O-ring was aged due to long-term exposure to high temperatures and could no longer seal. After replacing the O-ring, it returned to normal. The function of the wrong throttle is to introduce the high-pressure control oil and the low-pressure control oil after pressure relief into the upper and lower cylinders of the piston cylinder respectively, thereby controlling the opening of the valve. When the O-ring of the wrong throttle seal ages and leaks oil, the high-pressure oil and the oil after pressure relief cannot be separated, resulting in no pressure difference between the upper and lower cylinders of the piston, and of course the regulating valve cannot be closed.

2. The butterfly valve oscillates with constant amplitude

The furnace negative pressure regulating valve oscillates with constant amplitude and is controlled by a hand wheel. The inspection found that the throttle hole of the double nozzle amplifier was somewhat blocked, resulting in the balance pressure of the cylinder being too small and the pressure difference at both ends of the cylinder being too small. Therefore, the valve could not be stabilized, resulting in constant amplitude. oscillation. After cleaning the clogged orifice, the amplifier output increased and the butterfly valve operated normally.

3. Broken splint threads during calibration

When calibrating the regulating valve, the valve stem position needs to be adjusted. At this time, the calibration signal needs to be reduced to zero, and then the valve stem splint is loosened. As soon as it is loosened, only a banging sound is heard. When you see that the splint thread has been damaged, I had to re-process the plywood, assemble it and then calibrate it. The reason is that the calibration setter is used to reduce the signal to 0.2 MPa/cm 2 , but the pressure of the piston on the upper cylinder acts on the diaphragm head valve stem, and the loose splint cannot hold it, so the thread is opened. bad. Correct operation should open the balance piston between the upper and lower cylinders to balance the pressure in the upper and lower cylinders. Or remove the joint to let it deflate, then loosen the splint to adjust the valve stem.

4. The cylinder balance valve leaks and the regulating valve cannot operate]

Check the regulating valve after maintenance. The signal regulating valve cannot be opened. After inspection, it was discovered that the balance valve of the upper and lower cylinders was leaking, so the pressure difference between the upper and lower cylinders could not be formed. Replace the balance valve and return to normal.

5. The butterfly valve cannot be opened

The butterfly valve of the ammonia refiner could not be opened when it was put into operation after maintenance. The inspection found that the pipelines of the upper and lower cylinder air sources and pneumatic signals were connected in reverse during installation after maintenance. The takeover valve was corrected to operate normally. When the pneumatic signal pressure plus spring pressure is greater than the air source pressure, the butterfly valve is closed. When the pneumatic signal and the air source are connected reversely, the air source pressure plus the spring pressure is always greater than the pneumatic signal pressure, so the two-position butterfly valve is in a closed state.

6. The vent valve cannot be closed

The pressure regulating vent valve was subjected to grinding and pressure tests during an overhaul, and the sealing performance was very good. After reinstalling and starting the process normally, the valve needed to be closed tightly, but serious internal leakage was found. It is estimated that there is a foreign object stuck between the valve core and the valve seat. I decided to switch several times to flush out the foreign object. The test was successful and the valve was closed tightly and put into operation.