Source: Centralized Control Circle
#2机组高. Internal leakage and stuck operation of low-pressure bypass valve
Thing/Thing/Talk/Explanation
#2机组在机组运行期间出现高. In order to avoid the internal leakage and valve jamming phenomenon again in the operation of the unit, the problems and solutions found in the maintenance and the problems that the operators need to pay attention to in the process of operation are explained for your study and reference.
Situation/Situation/Explanation/Explanation
1. Analysis of the two low-pressure bypass valves of unit A and B of unit #2 have the problems of internal leakage and excessive opening torque that cannot be opened.
1. The reason for the internal leakage is: the spring at the lower part of the pre-start valve is too long, which causes the pre-start valve to not be closed, (after the spring is completely compressed, the sealing surface of the pre-start valve is not in contact). Solution: Lengthen the pre-start valve spool from the new design to ensure that the pre-start valve can be closed normally after the spring is completely compressed.
2. The reason for the excessive opening torque: after the pre-opening valve is fully opened, the upper part of the valve core of the pre-opening valve blocks the balance hole of the main valve, resulting in the pressure difference between the upper and lower parts of the main valve being too large, and the valve cannot be opened, and the pre-opening valve does not play a role in balancing the pressure difference between the upper and lower parts of the main valve. Solution: Drill holes around the spool of the pre-opening valve, so that after the pre-opening valve is opened, the airflow can enter the lower part of the valve through the balance hole, reduce the differential pressure up and down the main valve, and ensure that the valve can be opened normally.
II. #2机组高压旁路阀门内漏.
1. Cause of internal leakage of high side valve: after dismantling inspection, the sealing surface of the valve is normal and there is no erosion, and the dynamic and static sealing gasket between the valve core and the valve cage is completely washed out, which cannot play a sealing role, because the gap between the valve core and the valve cage is too large. Solution: Surfacing welding and repairing the outer circle of the valve core and the outer part of the upper gland of the valve core, and re-cooperate and install the valve cage.
Experience/experience/back/feed
Suggested actions:
1. Under the normal condition of the pneumatic device of the high and low side valves:
1. The low-pressure bypass valve can be switched on and off normally (the low-pressure bypass switch speed is slow); However, it is not recommended to carry out too much switching test for high-pressure bypass valve in the cold state of the unit, and too much activity test may lead to wear of the valve core sealing ring, shorten the service life, and even leakage.
2. In the initial stage of unit start-up; If conditions are met, the high and low pressure bypass valves should be opened in advance as far as possible, so that the opening torque can be reduced; In addition, the opening should be 20% or more to avoid the erosion of the spool sealing surface.
3. When the high side valve is withdrawn from use, it should be closed from 20% and above to 0 at one time to avoid scouring on the small opening sealing surface.
2. When the starting device of the high and low side valve cannot be operated remotely:
1. The operation personnel shall notify the on-site maintenance personnel that the pneumatic devices on the high and low sides cannot be operated remotely, and the maintenance personnel need to operate them professionally on the spot.
2. After receiving the notice of the operation personnel, the operation inspector and maintenance personnel will enter the scene to open and close the valve.
3. After determining the valve switch required by the operating personnel, the maintenance personnel shall prepare a special pin for the high and low side transmission device (the pin must be made of high-strength cylindrical, and items of different diameters are not allowed to be used as pins), and after inserting the pin into the connecting hole of the transmission device, the operation inspection personnel shall be notified to the operation inspection personnel, and the inspection personnel shall contact the disc to confirm the valve switch.
4. After connecting the transmission device, the maintenance personnel close the intake valve of the pneumatic actuator next to the high and low sides and open the cylinder balance valve.
5. After the valve has a certain opening, the required opening of the valve shall be determined by the personnel in front of the disk, and the inspection personnel shall be contacted to notify the on-site maintenance personnel to switch on.
6. After the unit starts, when the valve needs to be closed, the pre-disc personnel will contact the inspection personnel to notify the on-site maintenance personnel, and the monitoring personnel will not perform any operation during the period, and the maintenance personnel will quickly and manually close the valve.
7. After the valve is pressed, depending on the indication of the valve opening, the operator will arrange the feedback of the indication in a unified manner.
8. Thermal control personnel provide the logic of fast opening and fast closing in emergency situations.
#2机高旁阀压紧装置操作注意事项:
In normal operation, the manual door of the compressed air to the compression device is opened, and the pressure relief valve in the control cabinet is closed. If the switch of the solenoid valve operated remotely is not normal, close the main compressed air door on the spot, open the pressure relief valve, and the pressing device will exit.
Usually the inspection mainly to see whether the pressure of the hydraulic oil pressure gauge is correct, the high side valve is generally between 8-12MPa (the pressure gauge in the cabinet), if the pressure gauge is lower than the required value, it is possible that the booster pump is faulty or has oil leakage, the usual inspection needs to observe whether there is oil leakage in the pipeline, the hydraulic pump usually acts once in 20 minutes - 1 hour, if it is too frequent, the system may leak, and it needs to be checked. The oil level of the cylinder should not be lower than 20.
1. Pressing operation: DCS screen point pressing solenoid valve "closed", pressing solenoid valve power-off (green), compressed air into the booster pump, hydraulic cylinder piston rod slowly stretched out to the compression position.
2. Hydraulic exit operation: DCS screen point press the solenoid valve "open", press the solenoid valve live (red), close the compressed air, and slowly reach the exit position of the piston rod of the hydraulic cylinder.
Notes:
After the DCS screen compresses the solenoid valve switch operation, the solenoid valve status (red and green) only represents the command to switch the solenoid valve, not the position of the piston rod, and the action time of the piston rod is about 30S when compressed; When exiting, the action time is more than three minutes, so when it is necessary to operate the high side valve, open the compression solenoid valve, and then you need to go to the spot to confirm the actual position of the piston rod of the hydraulic cylinder (you can see it from standing on the ground).
At present, the piston rod of the hydraulic cylinder of the #2 high side valve is in the compression position, and the compression handwheel is also in the compression position, and when it is opened, it needs to be opened.
Instructions for use of high-side gas-liquid pressurization device:
1. Establishment of cylinder pressure
Close the high-pressure oil relief valve, open the compressed air intake valve, the gas-liquid booster pump starts to act, the pressure oil enters the hydraulic cylinder, the hydraulic cylinder slowly stretches out, when the hydraulic cylinder presses the cylinder rod stretched out by the pneumatic actuator, the valve core is affected by hydraulic pressure, and the valve core is more reliably compressed, and then the pressure rises, and the pressure value is between 7-10MPa. This sequence of operations is carried out after the high side valve is confirmed to close after the unit starts, and the pressure has been maintained since then.
2. The withdrawal of hydraulic force
When the unit needs a high side valve action, it needs to open the relief valve and close the inlet valve, which is exactly the opposite of the above action
3. The unit is in a shutdown state
When the unit is shut down, the relief valve needs to be opened and the compressed air inlet valve closed.
4. Establishment of remote control device
The solenoid valve is passed into the AC 220V power supply, the solenoid valve controls the unloading valve to work, the air source valve is closed, the unloading of the hydraulic device is controlled remotely, the power supply is disconnected to restore the work of the hydraulic device, and the valve is pressed, and the manual operation can still be carried out at this time, and it works the same as the above procedure 2.
5. Usual daily maintenance
The gas-liquid booster pump has the characteristics of simple structure and reliable operation, the usual inspection mainly depends on whether the pressure of the hydraulic oil pressure gauge is correct, the high side valve is generally between 8-12MPa, if the pressure gauge is lower than the required value, it is possible that the booster pump is faulty or has oil leakage, the usual inspection needs to observe whether there is oil leakage in the pipeline, the hydraulic pump usually acts once in 20 minutes - 1 hour, if it is too frequent, the system may leak, and it needs to be checked. The oil level of the cylinder should not be lower than 20