Matters Needing Attention When Operating Valves
May 12, 2023
When operating manual valves without a driving mechanism, it is generally stipulated that valves can be closed by clockwise rotation, and opened by counterclockwise rotation. When operating, you must see the mark well to avoid misoperation.
Handwheels and wrenches less than or equal to 320mm can only be operated by one person, and those above 320mm can be operated by two persons or one person with a booster rod not exceeding 0.5m. However, a booster rod is not allowed for diaphragm valves and valves with non-metallic sealing surfaces to prevent damage to the valves. Some people are used to using the booster rod, thinking that the greater the closing force is, the better it becomes, but it is wrong. Because the closing force is too great, the sealing pair and the valve stem thread bear more force. If the sealing pressure of the sealing pair and the yield limit of the thread are exceeded, deformation will occur; the sealing pair and the valve stem thread will fail, and the valve function will also fail. I saw some operators use an adjustable wrench to open and close the valve. I asked him. He said that the hand wheel or handle could not be found. I told him that it was very dangerous for him to operate like that. If the wrench slips, he may be injured. Therefore, the adjustable wrench cannot be used to open and close the valve, and the handwheel and wrench that are broken or lost on-site should be replaced in time.
When the steam valve is closed at high temperatures, but the pipeline stops running due to various reasons, the closed valve, especially the wedge gate valve should be opened slightly immediately to prevent the sealing pair from being seized and damaged. For valves installed on high-temperature pipelines, when the temperature rises above 200°C, the bolts of the middle flange will be heated and elongated, which will easily cause the static seal in the middle cavity of the valve body to leak. At this time, the bolts should be heat-tightened. Open the sealing pair a little to prevent the valve stem from being pushed up, making it difficult to open the valve in the future. When the valve is closed, the valve parts shrink due to the temperature drop, which will cause leakage due to the poor sealing of the sealing pair. When the ambient temperature drops to 0°C or below, open the plug or bottom valve at the bottom of the valve for idle valves to remove condensed water or accumulated water so as not to freeze the valve. For valves that cannot remove accumulated water, insulation measures should be taken to prevent the valve from freezing.
The packing gland should not be pressed too well, it will accelerate the wear of the valve stem, and increase the opening and closing torque of the valve stem. When replacing the packing, the upper seal should be closed. Replace packing, if necessary. The packing should be installed according to the specified number of turns, and packing that is used for a long time or aged should be replaced in time. The packing gland should be pressed symmetrically, and a pre-tightening gap of more than 5mm should be maintained.
When operating valves, abnormalities in pipelines and valves should be discovered by listening, smelling, watching, touching, and comparing. If it is within the scope of your responsibility, you should solve it in time. If it cannot be solved or the problem is relatively serious, you should report it in time and ask a repairman to solve it. Do not delay so that major accidents can be prevented.
Handwheels and wrenches less than or equal to 320mm can only be operated by one person, and those above 320mm can be operated by two persons or one person with a booster rod not exceeding 0.5m. However, a booster rod is not allowed for diaphragm valves and valves with non-metallic sealing surfaces to prevent damage to the valves. Some people are used to using the booster rod, thinking that the greater the closing force is, the better it becomes, but it is wrong. Because the closing force is too great, the sealing pair and the valve stem thread bear more force. If the sealing pressure of the sealing pair and the yield limit of the thread are exceeded, deformation will occur; the sealing pair and the valve stem thread will fail, and the valve function will also fail. I saw some operators use an adjustable wrench to open and close the valve. I asked him. He said that the hand wheel or handle could not be found. I told him that it was very dangerous for him to operate like that. If the wrench slips, he may be injured. Therefore, the adjustable wrench cannot be used to open and close the valve, and the handwheel and wrench that are broken or lost on-site should be replaced in time.
When the steam valve is closed at high temperatures, but the pipeline stops running due to various reasons, the closed valve, especially the wedge gate valve should be opened slightly immediately to prevent the sealing pair from being seized and damaged. For valves installed on high-temperature pipelines, when the temperature rises above 200°C, the bolts of the middle flange will be heated and elongated, which will easily cause the static seal in the middle cavity of the valve body to leak. At this time, the bolts should be heat-tightened. Open the sealing pair a little to prevent the valve stem from being pushed up, making it difficult to open the valve in the future. When the valve is closed, the valve parts shrink due to the temperature drop, which will cause leakage due to the poor sealing of the sealing pair. When the ambient temperature drops to 0°C or below, open the plug or bottom valve at the bottom of the valve for idle valves to remove condensed water or accumulated water so as not to freeze the valve. For valves that cannot remove accumulated water, insulation measures should be taken to prevent the valve from freezing.
The packing gland should not be pressed too well, it will accelerate the wear of the valve stem, and increase the opening and closing torque of the valve stem. When replacing the packing, the upper seal should be closed. Replace packing, if necessary. The packing should be installed according to the specified number of turns, and packing that is used for a long time or aged should be replaced in time. The packing gland should be pressed symmetrically, and a pre-tightening gap of more than 5mm should be maintained.
When operating valves, abnormalities in pipelines and valves should be discovered by listening, smelling, watching, touching, and comparing. If it is within the scope of your responsibility, you should solve it in time. If it cannot be solved or the problem is relatively serious, you should report it in time and ask a repairman to solve it. Do not delay so that major accidents can be prevented.
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