(1) Diaphragm membrane head actuator
1. The liquid level control regulating valve is out of control and cannot be opened
The liquid level measurement indication is already very high, and the output of the regulator is also very large, but the regulating valve cannot be opened, so the mechanical handwheel has to be used for control. Check the valve positioner (remove the connecting pipe of the membrane head and plug it up), press the nozzle baffle mechanism, there is no output change of the positioner, check that the orifice is unobstructed, disassemble the amplifier and find that the amplifier diaphragm is broken. Replace the diaphragm, and the regulating valve is put into automatic control again. The valve positioner amplifier diaphragm 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 feedback slider of the valve positioner is rusted
The liquid level fluctuated violently. Inspection found that the slide bar of the feedback mechanism of the valve positioner was completely rusted and could not be rotated, so the handwheel had to be used to control it. Managed to knock out the slide rod, put it back after rusting and oiling, and the regulating valve returned to normal. The feedback mechanism of the valve positioner adds the corresponding feedback amount of the positioner as the opening of the valve changes. The slide rod is rusted, and the feedback force cannot change with the opening of the valve, and the opening of the valve cannot be stopped at the corresponding position of the regulator output signal, resulting in continuous fluctuation of the liquid level.
3. The pressure control valve cannot operate
Once the process load is reduced, the natural gas volume cannot be reduced, which is caused by the failure of the natural gas pressure regulating valve. During the inspection, it was found that the output signal of the valve was normal, and it was estimated that the valve core was stuck due to carbon formation, and then the valve was closed by increasing the aerodynamic signal and adding the force of the handwheel. After parking the valve, the valve was disassembled for inspection. As expected, because the valve has little load stability switch at ordinary times, the carbon black contained in the natural gas is stuck in the small gap between the valve stem and the guide sleeve. Therefore, during the annual overhaul, the valve will be disassembled and cleaned to avoid similar accidents. Today's focus:
Four, the spool breaks out of control
The liquid level of the absorption tower cannot be controlled, and the fluctuation of the record curve drops, and there is no problem in checking the transmitter and regulator. When controlling the handwheel, it is found that the handwheel is not as heavy as usual when it is pressed down or lifted up. It is judged that the valve core is broken, and it is forced to stop and disassemble the regulating valve. The connection between the valve core and the valve stem is disconnected. The spool had to be replaced, and the joint of the spool and stem was surfacing to increase the strength to avoid similar accidents. The fracture of the spool is caused by the unbalanced force under the medium pressure.
5. The multi-regulating valve with packing cannot be opened
When driving after the overhaul, the liquid level in the liquid ammonia flash tank was high. On-site inspection found that the regulating valve was not opened, and hurriedly turned the handwheel to control the liquid level. Too much, too tight, friction. Appropriately loosen the packing and pressure so that it can move flexibly and re-enter with self-control.
Six, flow control fluctuations
The anti-surge flow control vent valve of the air compressor is frequently switched on and off during the start-up process, resulting in unstable flow. There is no problem in checking the regulator and regulating valve, but the opening of the regulating valve has been very small. When the air flow rate rises, the regulator outputs a signal up to 1 MPa/cm 2 to the regulating valve (air-closing 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 takes control. The low-end control of the control valve has poor linearity, so the valve must switch frequently, which makes the flow control unstable. The only solution is to suggest that the process increase the speed of the compressor, increase the venting capacity, and disengage the control valve from the low-end control.
7. Low liquid level alarm in the absorption tower
Check that the regulating valve is fully closed, so it has to cooperate with the process to reverse the operation of the B valve. Disassemble the valve and check that the spool is seriously damaged by erosion. Replace the new spool and install it for backup. The spool is eroded and cannot be controlled. If it is not dealt with in time, the liquid level will be lower than the interlock liquid level, which will cause shutdown.
8. The stem of the regulating valve is bent and cannot be opened
After the overhaul, the liquid level control valve of the absorption tower could not be opened while driving. It was found that the valve stem was bent during maintenance, so the valve stem had to be disassembled, removed, straightened, reinstalled, and put into operation. Care must be taken when inspecting and repairing the regulating valve, especially for valves with a non-splint connection structure, the diaphragm head is heavy, and the diaphragm head needs to be turned for the first few turns of the turnbuckle, which may bend the valve stem if you are not careful. In addition, after the regulating valve has been overhauled, installed and calibrated, it should be switched on and off several times to make sure that its action is very flexible before giving up.
Nine, the control valve can not move
During the driving process after the overhaul, it was found that the liquid level control valve of the absorption tower could not operate, and it was forced to stop and open the regulating valve for inspection. The iron filings that fell between the guide sleeve and the valve stem were stuck. During the overhaul of the valve, the old guide sleeve of the lower flange was cut off with a lathe, and a new guide sleeve was replaced. When the valve was assembled, the cleaning was not careful, and there were iron filings falling under the guide sleeve. When the valve was calibrated, The iron filings below did not hinder the movement of the valve, and no problems were found. After driving into the medium, the medium rushes into the guide sleeve from the balance hole, and then flows out of the balance hole from 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. up.
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 plug controlled by the mechanical hand wheel was not pulled out, and the regulating valve was in the mechanical manual closed position, of course it could not be opened. Adjust the output signal of the regulator to zero, and after unplugging the plug, the regulating valve is put into operation.
11. It is found that the regulating valve has friction
The natural gas pressure control valve was found to have poor friction after overhaul, resulting in pressure fluctuations. The reason for the friction is that the friction phenomenon after the gland flange is eliminated during inspection and assembly.
Generally, the gap between the valve stem and the guide sleeve of the regulating valve is very small, and the gland flange must be flattened during assembly, otherwise there will be either leakage or friction caused by the discrepancy between the valve stem and the guide sleeve.
12. Sudden full closing of the regulating valve causes parking
The natural gas flow regulating valve was suddenly fully closed, the natural gas flow rate 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, operate the handwheel, and resume production in conjunction with the process. Remove the output air pipe of the positioner, plug it by hand, press the nozzle baffle mechanism, the output signal can reach 1MPa/cm 2 , indicating that the problem lies in the regulating valve, send air signal to the membrane head, and there is gas in the vent hole of the membrane head released, it proves that the diaphragm is broken. Replace the diaphragm regulating valve and put it into operation.
13. Switching automatically causes system disturbance
The steam flow regulating valve is controlled by the handwheel at the first stage. After checking the locator, it will be reactivated automatically. When the handwheel is released, the system will be disturbed. The reason is that the output signal of the regulator is maintained at the value before the manual operation, and the operator quickly releases the handwheel without looking at the output of the positioner, and the regulating valve opens accordingly. Because the membrane head is too large, there is an inflation lag process, which causes the air-off valve to open much larger suddenly, causing a disturbance to the system.
Fourteen, deal with the leakage of gas source
When dealing with the air leakage of 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 hands, and restored the original position of the regulating valve, and then cooperated with the operator to control the regulating valve with the handwheel and replace the joint. It is also very effective to take this emergency measure in an emergency.
15. The diaphragm valve cannot be opened
The water treatment regeneration discharge valve could not be opened, and it was disassembled for inspection, and the diaphragm was found to be damaged. After replacing the new diaphragm, it could not be opened again within a few days, and the above situation happened again. The cause of the broken diaphragm is analyzed because the limit bolt of the diaphragm valve diaphragm head is loose, the limit position has changed, the stroke of the valve stem is too large, and the pulling force exceeds the elastic range of the diaphragm, so the diaphragm is broken. Readjust the limit bolt, replace the diaphragm again, 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 the signal could not be closed. The inspection found that the O-ring of the wrong throttle was soaked and aged at high temperature for a long time, and it was not able to 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, so as to control the opening of the valve. When the wrong throttle seal O-ring ages and leaks oil, the high-pressure oil and the pressure-released oil 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 equal amplitude
The negative pressure regulating valve of the furnace oscillates in equal amplitude, and the joint is controlled by the hand wheel. It is found that the orifice of the double nozzle amplifier is somewhat blocked, resulting in too small balance pressure of the cylinder, and the pressure difference between the two ends of the cylinder is too small, so the valve cannot be stabilized, resulting in constant amplitude. oscillation. After cleaning the clogged orifice, the output of the amplifier increases and the butterfly valve operates normally.
3. Break the splint thread during calibration
When calibrating the regulating valve, it is necessary to adjust the position of the valve stem. At this time, the calibration signal needs to be reduced to zero, and then the splint of the valve stem is loosened. As soon as it is loosened, only a bang sound is heard, and the thread of the splint has been broken. Had to reprocess the splint and assemble it before calibration. The reason is that the signal is lowered to 0.2 MPa/cm 2 by the constant value device for calibration, but the pressure of the piston on the upper cylinder acts on the valve stem of the membrane head, and the loose splint cannot support it, so the screw thread is screwed. bad. The correct operation should open the balance piston between the upper and lower cylinders to balance the pressure of the upper and lower cylinders. Or disassemble the joint to let it deflate, and then loosen the splint to adjust the valve stem.
4. The cylinder balance valve leakage regulating valve cannot operate]
Check the regulating valve after overhaul, and the regulating valve cannot be opened when the signal is sent. It was only after the inspection that the balance valve of the upper and lower cylinders leaked air, 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 ammonia refiner butterfly valve cannot be opened when it is put into operation after overhaul. The inspection found that the gas source and pneumatic signal pipelines of the upper and lower cylinders were connected reversely during installation after overhaul, and the connection valve was corrected for normal operation. When the pneumatic signal pressure plus the spring pressure is greater than the air source pressure, the butterfly valve is closed. When the pneumatic signal and the air source are reversely connected, the pressure of the air source plus the spring pressure is always greater than the pressure of the pneumatic signal, so the two-position butterfly valve is in a closed state.
6. The vent valve cannot be closed
The pressure regulating vent valve has undergone grinding and pressure tests during an overhaul, and the sealing performance is very good. After putting it back and starting the process normally, the valve needs to be closed tightly, but serious internal leakage is found. It is estimated that a foreign matter is stuck between the valve core and the seat, and it is decided to switch several times to flush out the foreign matter. The test is successful, and the valve is tightly closed and put into operation.
(1) Diaphragm membrane head actuator
1. The liquid level control regulating valve is out of control and cannot be opened
The liquid level measurement indication is already very high, and the output of the regulator is also very large, but the regulating valve cannot be opened, so the mechanical handwheel has to be used for control. Check the valve positioner (remove the connecting pipe of the membrane head and plug it up), press the nozzle baffle mechanism, there is no output change of the positioner, check that the orifice is unobstructed, disassemble the amplifier and find that the amplifier diaphragm is broken. Replace the diaphragm, and the regulating valve is put into automatic control again. The valve positioner amplifier diaphragm 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 feedback slider of the valve positioner is rusted
The liquid level fluctuated violently. Inspection found that the slide bar of the feedback mechanism of the valve positioner was completely rusted and could not be rotated, so the handwheel had to be used to control it. Managed to knock out the slide rod, put it back after rusting and oiling, and the regulating valve returned to normal. The feedback mechanism of the valve positioner adds the corresponding feedback amount of the positioner as the opening of the valve changes. The slide rod is rusted, and the feedback force cannot change with the opening of the valve, and the opening of the valve cannot be stopped at the corresponding position of the regulator output signal, resulting in continuous fluctuation of the liquid level.
3. The pressure control valve cannot operate
Once the process load is reduced, the natural gas volume cannot be reduced, which is caused by the failure of the natural gas pressure regulating valve. During the inspection, it was found that the output signal of the valve was normal, and it was estimated that the valve core was stuck due to carbon formation, and then the valve was closed by increasing the aerodynamic signal and adding the force of the handwheel. After parking the valve, the valve was disassembled for inspection. As expected, because the valve has little load stability switch at ordinary times, the carbon black contained in the natural gas is stuck in the small gap between the valve stem and the guide sleeve. Therefore, during the annual overhaul, the valve will be disassembled and cleaned to avoid similar accidents. Today's focus:
Four, the spool breaks out of control
The liquid level of the absorption tower cannot be controlled, and the fluctuation of the record curve drops, and there is no problem in checking the transmitter and regulator. When controlling the handwheel, it is found that the handwheel is not as heavy as usual when it is pressed down or lifted up. It is judged that the valve core is broken, and it is forced to stop and disassemble the regulating valve. The connection between the valve core and the valve stem is disconnected. The spool had to be replaced, and the joint of the spool and stem was surfacing to increase the strength to avoid similar accidents. The fracture of the spool is caused by the unbalanced force under the medium pressure.
5. The multi-regulating valve with packing cannot be opened
When driving after the overhaul, the liquid level in the liquid ammonia flash tank was high. On-site inspection found that the regulating valve was not opened, and hurriedly turned the handwheel to control the liquid level. Too much, too tight, friction. Appropriately loosen the packing and pressure so that it can move flexibly and re-enter with self-control.
Six, flow control fluctuations
The anti-surge flow control vent valve of the air compressor is frequently switched on and off during the start-up process, resulting in unstable flow. There is no problem in checking the regulator and regulating valve, but the opening of the regulating valve has been very small. When the air flow rate rises, the regulator outputs a signal up to 1 MPa/cm 2 to the regulating valve (air-closing 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 takes control. The low-end control of the control valve has poor linearity, so the valve must switch frequently, which makes the flow control unstable. The only solution is to suggest that the process increase the speed of the compressor, increase the venting capacity, and disengage the control valve from the low-end control.
7. Low liquid level alarm in the absorption tower
Check that the regulating valve is fully closed, so it has to cooperate with the process to reverse the operation of the B valve. Disassemble the valve and check that the spool is seriously damaged by erosion. Replace the new spool and install it for backup. The spool is eroded and cannot be controlled. If it is not dealt with in time, the liquid level will be lower than the interlock liquid level, which will cause shutdown.
8. The stem of the regulating valve is bent and cannot be opened
After the overhaul, the liquid level control valve of the absorption tower could not be opened while driving. It was found that the valve stem was bent during maintenance, so the valve stem had to be disassembled, removed, straightened, reinstalled, and put into operation. Care must be taken when inspecting and repairing the regulating valve, especially for valves with a non-splint connection structure, the diaphragm head is heavy, and the diaphragm head needs to be turned for the first few turns of the turnbuckle, which may bend the valve stem if you are not careful. In addition, after the regulating valve has been overhauled, installed and calibrated, it should be switched on and off several times to make sure that its action is very flexible before giving up.
Nine, the control valve can not move
During the driving process after the overhaul, it was found that the liquid level control valve of the absorption tower could not operate, and it was forced to stop and open the regulating valve for inspection. The iron filings that fell between the guide sleeve and the valve stem were stuck. During the overhaul of the valve, the old guide sleeve of the lower flange was cut off with a lathe, and a new guide sleeve was replaced. When the valve was assembled, the cleaning was not careful, and there were iron filings falling under the guide sleeve. When the valve was calibrated, The iron filings below did not hinder the movement of the valve, and no problems were found. After driving into the medium, the medium rushes into the guide sleeve from the balance hole, and then flows out of the balance hole from 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. up.
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 plug controlled by the mechanical hand wheel was not pulled out, and the regulating valve was in the mechanical manual closed position, of course it could not be opened. Adjust the output signal of the regulator to zero, and after unplugging the plug, the regulating valve is put into operation.
11. It is found that the regulating valve has friction
The natural gas pressure control valve was found to have poor friction after overhaul, resulting in pressure fluctuations. The reason for the friction is that the friction phenomenon after the gland flange is eliminated during inspection and assembly.
Generally, the gap between the valve stem and the guide sleeve of the regulating valve is very small, and the gland flange must be flattened during assembly, otherwise there will be either leakage or friction caused by the discrepancy between the valve stem and the guide sleeve.
12. Sudden full closing of the regulating valve causes parking
The natural gas flow regulating valve was suddenly fully closed, the natural gas flow rate 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, operate the handwheel, and resume production in conjunction with the process. Remove the output air pipe of the positioner, plug it by hand, press the nozzle baffle mechanism, the output signal can reach 1MPa/cm 2 , indicating that the problem lies in the regulating valve, send air signal to the membrane head, and there is gas in the vent hole of the membrane head released, it proves that the diaphragm is broken. Replace the diaphragm regulating valve and put it into operation.
13. Switching automatically causes system disturbance
The steam flow regulating valve is controlled by the handwheel at the first stage. After checking the locator, it will be reactivated automatically. When the handwheel is released, the system will be disturbed. The reason is that the output signal of the regulator is maintained at the value before the manual operation, and the operator quickly releases the handwheel without looking at the output of the positioner, and the regulating valve opens accordingly. Because the membrane head is too large, there is an inflation lag process, which causes the air-off valve to open much larger suddenly, causing a disturbance to the system.
Fourteen, deal with the leakage of gas source
When dealing with the air leakage of 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 hands, and restored the original position of the regulating valve, and then cooperated with the operator to control the regulating valve with the handwheel and replace the joint. It is also very effective to take this emergency measure in an emergency.
15. The diaphragm valve cannot be opened
The water treatment regeneration discharge valve could not be opened, and it was disassembled for inspection, and the diaphragm was found to be damaged. After replacing the new diaphragm, it could not be opened again within a few days, and the above situation happened again. The cause of the broken diaphragm is analyzed because the limit bolt of the diaphragm valve diaphragm head is loose, the limit position has changed, the stroke of the valve stem is too large, and the pulling force exceeds the elastic range of the diaphragm, so the diaphragm is broken. Readjust the limit bolt, replace the diaphragm again, 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 the signal could not be closed. The inspection found that the O-ring of the wrong throttle was soaked and aged at high temperature for a long time, and it was not able to 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, so as to control the opening of the valve. When the wrong throttle seal O-ring ages and leaks oil, the high-pressure oil and the pressure-released oil 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 equal amplitude
The negative pressure regulating valve of the furnace oscillates in equal amplitude, and the joint is controlled by the hand wheel. It is found that the orifice of the double nozzle amplifier is somewhat blocked, resulting in too small balance pressure of the cylinder, and the pressure difference between the two ends of the cylinder is too small, so the valve cannot be stabilized, resulting in constant amplitude. oscillation. After cleaning the clogged orifice, the output of the amplifier increases and the butterfly valve operates normally.
3. Break the splint thread during calibration
When calibrating the regulating valve, it is necessary to adjust the position of the valve stem. At this time, the calibration signal needs to be reduced to zero, and then the splint of the valve stem is loosened. As soon as it is loosened, only a bang sound is heard, and the thread of the splint has been broken. Had to reprocess the splint and assemble it before calibration. The reason is that the signal is lowered to 0.2 MPa/cm 2 by the constant value device for calibration, but the pressure of the piston on the upper cylinder acts on the valve stem of the membrane head, and the loose splint cannot support it, so the screw thread is screwed. bad. The correct operation should open the balance piston between the upper and lower cylinders to balance the pressure of the upper and lower cylinders. Or disassemble the joint to let it deflate, and then loosen the splint to adjust the valve stem.
4. The cylinder balance valve leakage regulating valve cannot operate]
Check the regulating valve after overhaul, and the regulating valve cannot be opened when the signal is sent. It was only after the inspection that the balance valve of the upper and lower cylinders leaked air, 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 ammonia refiner butterfly valve cannot be opened when it is put into operation after overhaul. The inspection found that the gas source and pneumatic signal pipelines of the upper and lower cylinders were connected reversely during installation after overhaul, and the connection valve was corrected for normal operation. When the pneumatic signal pressure plus the spring pressure is greater than the air source pressure, the butterfly valve is closed. When the pneumatic signal and the air source are reversely connected, the pressure of the air source plus the spring pressure is always greater than the pressure of the pneumatic signal, so the two-position butterfly valve is in a closed state.
6. The vent valve cannot be closed
The pressure regulating vent valve has undergone grinding and pressure tests during an overhaul, and the sealing performance is very good. After putting it back and starting the process normally, the valve needs to be closed tightly, but serious internal leakage is found. It is estimated that a foreign matter is stuck between the valve core and the seat, and it is decided to switch several times to flush out the foreign matter. The test is successful, and the valve is tightly closed and put into operation.