The accident caused by operation of valves
People often care about the operation of the main equipment, but they think that the operation for the valve is simple and not enough attention has been paid. However, explosions and personal accidents occur from time to time due to misoperation of valves, causing great losses. For example, once there was a major accident due to a closed valve that was supposed to be opened because of misoperation on the Irish Nuclear Power Plant on Three Mile Island in the United States. There have also been accidents involving valve misoperation in nuclear power plants in Japan. Occasional accidents happen for some petrochemical plants, steel plants, and power plants. A series of accidents show that how important the operation of the valve is to the normal operation of the equipment, especially in nuclear power plants. Once an accident occurs, it may cause radioactive leakage. Therefore, no matter what factory it is, the correct operation of the valve should be paid great attention to.
Points for attention for operation of valves
Precautions for operation of valves
2.2.1 General matters
(1) In terms of the operation of valves, a responsible operator should be a person who has been through comprehensive training according to the training plan, qualified for technical internships, and can give full play to his technical capabilities.
(2) For a new operator, he must ensure that there should be sufficient training time. Before he operates alone, the operation should be carried out with the cooperation of skilled operators.
(3) A normative system related to the operation of valves should be compiled.
(4) For unconventional operations, an inspection and operation program diagram should be compiled.
(5) Sometimes the operation is performed according to the superior instruction, and the instruction must be repeated to confirm that it is correct. When starting operation, also confirm the designated valve.
2.2.2 Manual operation for valves
(1) Always get in touch with the instrument room when operating the valve, and be sure to report after the operation is completed.
(2) The operation of the valve should be gentle to prevent noise, vibration, and leakage.
(3) When there is an emergency, the operation must be especially cautious.
(4) When there are flow meters, thermometers, pressure gauges, and other instruments near the operating posts, please pay attention to the instruments while operating.
(5) Check the valve's opening and closing signs and the degree of opening and closing (being fully open or fully closed).
2.2.3 Operation of automatic valves
(1) The automatic valve can be operated only after mastering the display characteristics of the instrument on the operation amount, change amount, time lag, etc.
(2) In the event of an emergency, the manual operation needs to be changed in accordance with relevant standards.
(3) Frequently check and make sure that the air source, power supply and other facilities used for operation work well.
(4) In the operation of automatic valves, the hysteresis error of the valve must be taken into account frequently in order to operate accurately.
(5) At the beginning and during the operation, the instrument must be adjusted to make the action correct and ensure the reliability of the instrument.
(6) Read the operating instructions of the valve carefully and comprehensively, and fully understand the contents.
Opening and closing of manual valves
The manual valve is the most widely used valve. Its hand wheel or handle is designed according to ordinary human strength, which takes into account the strength of the sealing surface and the necessary closing force. Therefore, you cannot use a long lever or a long wrench to turn the valve. Some people are accustomed to using wrenches, and they should be careful not to use too much force. Otherwise, it is easy to damage the sealing surface, or break the hand wheel and handle. When opening and closing the valve, the force should be steady without impact.
For the steam valve, it should be pre-heated and the condensed water should be removed before opening. Open the valve as slow as possible to avoid water hammer. When the valve is fully opened, the handwheel should be turned upside down to make the threads tightly to avoid loosening and damage.
For rising stem valves, remember positions of the valve stem when they are fully opened and closed to avoid hitting the top dead center at a fully open state. It is convenient to check whether it is normal when fully closed. If the valve clack falls off, or big debris embeds between the sealing of valve spools, the position of the valve stem will change when it is fully closed.
When the pipeline is first used, there is a lot of internal dirt. You can open the valve slightly; use the high-speed flow of the medium to wash it away, and then close it gently. Don't close the valve quickly to prevent residual impurities from scratching the sealing surface. Open the valve again. Keep opening the valve many times to flush the dirt before putting into use.
Some medium cools down after the valve is closed, causing the valve to shrink. The operator should close it again at an appropriate time so that the sealing surface does not leave any crevice. Otherwise, the medium will flow through the crevices at high speed and it will easily erode the sealing surface. During operation, if the operation is too laborious, you should analyze the reason. If the packing is too tight, it can be properly loosened. If the valve stem is skewed, the personnel should be notified for repair. For some valves, the closing part is heated and expanded when they are closed, which makes it difficult to open. If it must be opened at this time, loosen the bonnet's thread by half a turn to one turn to eliminate the stress on the valve stem, and then turn the handwheel.
People often care about the operation of the main equipment, but they think that the operation for the valve is simple and not enough attention has been paid. However, explosions and personal accidents occur from time to time due to misoperation of valves, causing great losses. For example, once there was a major accident due to a closed valve that was supposed to be opened because of misoperation on the Irish Nuclear Power Plant on Three Mile Island in the United States. There have also been accidents involving valve misoperation in nuclear power plants in Japan. Occasional accidents happen for some petrochemical plants, steel plants, and power plants. A series of accidents show that how important the operation of the valve is to the normal operation of the equipment, especially in nuclear power plants. Once an accident occurs, it may cause radioactive leakage. Therefore, no matter what factory it is, the correct operation of the valve should be paid great attention to.
Points for attention for operation of valves
Precautions for operation of valves
2.2.1 General matters
(1) In terms of the operation of valves, a responsible operator should be a person who has been through comprehensive training according to the training plan, qualified for technical internships, and can give full play to his technical capabilities.
(2) For a new operator, he must ensure that there should be sufficient training time. Before he operates alone, the operation should be carried out with the cooperation of skilled operators.
(3) A normative system related to the operation of valves should be compiled.
(4) For unconventional operations, an inspection and operation program diagram should be compiled.
(5) Sometimes the operation is performed according to the superior instruction, and the instruction must be repeated to confirm that it is correct. When starting operation, also confirm the designated valve.
2.2.2 Manual operation for valves
(1) Always get in touch with the instrument room when operating the valve, and be sure to report after the operation is completed.
(2) The operation of the valve should be gentle to prevent noise, vibration, and leakage.
(3) When there is an emergency, the operation must be especially cautious.
(4) When there are flow meters, thermometers, pressure gauges, and other instruments near the operating posts, please pay attention to the instruments while operating.
(5) Check the valve's opening and closing signs and the degree of opening and closing (being fully open or fully closed).
2.2.3 Operation of automatic valves
(1) The automatic valve can be operated only after mastering the display characteristics of the instrument on the operation amount, change amount, time lag, etc.
(2) In the event of an emergency, the manual operation needs to be changed in accordance with relevant standards.
(3) Frequently check and make sure that the air source, power supply and other facilities used for operation work well.
(4) In the operation of automatic valves, the hysteresis error of the valve must be taken into account frequently in order to operate accurately.
(5) At the beginning and during the operation, the instrument must be adjusted to make the action correct and ensure the reliability of the instrument.
(6) Read the operating instructions of the valve carefully and comprehensively, and fully understand the contents.
Opening and closing of manual valves
The manual valve is the most widely used valve. Its hand wheel or handle is designed according to ordinary human strength, which takes into account the strength of the sealing surface and the necessary closing force. Therefore, you cannot use a long lever or a long wrench to turn the valve. Some people are accustomed to using wrenches, and they should be careful not to use too much force. Otherwise, it is easy to damage the sealing surface, or break the hand wheel and handle. When opening and closing the valve, the force should be steady without impact.
For the steam valve, it should be pre-heated and the condensed water should be removed before opening. Open the valve as slow as possible to avoid water hammer. When the valve is fully opened, the handwheel should be turned upside down to make the threads tightly to avoid loosening and damage.
For rising stem valves, remember positions of the valve stem when they are fully opened and closed to avoid hitting the top dead center at a fully open state. It is convenient to check whether it is normal when fully closed. If the valve clack falls off, or big debris embeds between the sealing of valve spools, the position of the valve stem will change when it is fully closed.
When the pipeline is first used, there is a lot of internal dirt. You can open the valve slightly; use the high-speed flow of the medium to wash it away, and then close it gently. Don't close the valve quickly to prevent residual impurities from scratching the sealing surface. Open the valve again. Keep opening the valve many times to flush the dirt before putting into use.
Some medium cools down after the valve is closed, causing the valve to shrink. The operator should close it again at an appropriate time so that the sealing surface does not leave any crevice. Otherwise, the medium will flow through the crevices at high speed and it will easily erode the sealing surface. During operation, if the operation is too laborious, you should analyze the reason. If the packing is too tight, it can be properly loosened. If the valve stem is skewed, the personnel should be notified for repair. For some valves, the closing part is heated and expanded when they are closed, which makes it difficult to open. If it must be opened at this time, loosen the bonnet's thread by half a turn to one turn to eliminate the stress on the valve stem, and then turn the handwheel.
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