When to Replace Your Valve Packing?

In industrial production, valves are key devices for controlling fluid flow, and the packing gland is an essential part of valve sealing. If the packing in the packing gland develops issues, it may lead to media leakage, which not only affects production efficiency but can also cause safety accidents. Therefore, it is crucial to promptly determine whether the packing needs replacement. This article will provide a detailed introduction on how to determine if valve packing needs replacement, helping everyone better maintain valve equipment.

The most intuitive method is to observe whether there is media leakage around the packing gland. If you see liquid dripping, seeping, or vapor escaping (for volatile media) at the valve stem (i.e., the packing gland location), this is a clear indication of packing seal failure. For gaseous media, you can apply soapy water around the packing gland; if bubbles appear, it indicates gas leakage. Minor leakage may manifest as slight dampness or tiny droplets around the packing gland. This situation may not temporarily affect the normal use of the valve, but it requires close monitoring. If the leakage is severe, such as continuous liquid flow or a large amount of gas leakage, affecting the working environment or failing to meet process requirements (for example, in chemical production, leakage may cause safety accidents or product quality issues), the packing needs to be replaced immediately.

When operating the valve (manually or electrically) to open and close it, if you feel a significant increase in the operating force, it may be due to increased friction between the packing and the valve stem. This could be because the packing has become compact after wear, or it has aged and dried out, losing its elasticity, resulting in tighter contact with the valve stem. For example, if a handwheel that used to turn easily now requires much more effort to operate, this is a signal that the packing may need replacement. During valve operation, pay attention to the movement of the valve stem. If the valve stem moves unevenly, with sticking or shaking, in addition to considering issues with the valve stem itself, it may also be due to uneven friction from the packing. This could be caused by packing wear, damage, or improper installation. For instance, partial damage to the packing may cause inconsistent resistance during the valve stem's movement, leading to sticking.

When the valve is undergoing regular maintenance or if you suspect there is an issue with the packing, you can open the packing gland cover (if possible) to inspect the packing's appearance. If the packing shows signs of hardening, brittleness, or discoloration (for example, if the originally black graphite packing turns grayish-white, it may have been chemically eroded), this indicates that the packing has aged or undergone chemical changes. Aged packing cannot effectively fill the gap between the valve stem and the packing gland, leading to leakage. Observe whether the packing is worn. Under normal circumstances, there will be a certain degree of friction between the packing and the valve stem. With increased time and usage, the packing will gradually wear out. If the packing is severely worn, its thickness will be significantly reduced, and it will no longer provide sufficient sealing force, necessitating replacement. For example, for woven packing, if the woven structure is loose or fibers are broken, it indicates severe wear. Press the packing with your finger to check its elasticity. If the packing has lost its elasticity and does not return to its original shape after pressing, this means that the packing's sealing performance has declined. Packing with good elasticity can adaptively fill the gap during the valve stem's movement, maintaining a good sealing effect.

Review the valve's maintenance records. If the packing has been repaired multiple times before, such as adding packing or adjusting the packing gland cover, but leakage or abnormal operating force still occurs, it is likely that the packing cannot restore its performance through simple repairs and needs to be replaced. Based on the valve's usage frequency and working environment, roughly estimate the packing's service life. Generally, in a normal working environment, the packing's service life may range from one to several years. For example, in the chemical industry, valves that are frequently operated and in contact with corrosive media may need to replace their packing within about a year. In contrast, in ordinary water supply and drainage systems, the service life may be relatively longer. If the valve has been in use for a long time and the aforementioned leakage or changes in operating force occur, replacing the packing is a prudent approach.

When severe or frequent leakage is detected after valve operation, it may indicate that the valve stem sealing packing has aged or worn severely and needs to be replaced promptly. If the valve feels stiff, requires excessive force, or sticks during operation, it may be due to damaged valve stem sealing packing that needs inspection and replacement. A decline in the sealing performance of the valve stem sealing packing can lead to the valve not closing effectively, resulting in media leakage. In such cases, the valve stem sealing packing should be replaced to restore sealing performance. Prolonged use of the valve stem sealing packing or its exposure to media can cause it to age, harden, and lose elasticity, leading to ineffective valve sealing. Replacement is necessary in these situations. To determine whether the valve stem sealing packing needs replacement, the following methods can be used for inspection:

Observe whether there is obvious leakage during valve operation, whether there is seepage or media residue around the valve stem, and whether there are signs of wear or aging on the packing's appearance to make a preliminary judgment on whether the packing needs replacement.

Touch the packing to see if it feels significantly hardened or brittle. If the packing surface is not smooth and shows obvious wear or damage, replacement is required.

Place a clean piece of paper or a hygrometer around the valve during operation to observe for seepage. If there is obvious seepage, it indicates that the valve stem sealing packing may need replacement.

Conduct a pressure test on the valve to assess its sealing performance. If the test results show poor sealing performance, it is likely due to issues with the valve stem sealing packing, and replacement is necessary.

When it is determined that the valve stem sealing packing needs to be replaced, appropriate packing material and specifications should be selected to ensure the normal operation and sealing performance of the valve. The following points should be noted when replacing the valve stem sealing packing.

• Close the valve and empty the system: Before replacing the packing, it is essential to ensure that the valve is in the closed position and that all media in the system have been completely drained. This prevents media leakage during the replacement process, avoiding personal injury or environmental pollution.
• Exercise caution when removing old packing: When removing old packing, be careful to avoid damaging the valve. Special tools, such as packing hooks, can be used to remove the old packing in a circular manner. If the packing has hardened or adhered to the valve stem, it can be soaked in an appropriate solvent to soften it before removal.
• Clean and lubricate the valve stem surface: Before installing new packing, the valve stem surface should be cleaned and lubricated. Use a clean cloth or cotton to wipe the valve stem surface, removing any residual old packing, impurities, and rust. Then, apply an appropriate amount of lubricating grease or graphite powder to the valve stem surface to reduce friction between the new packing and the valve stem, ensuring the new packing can be installed smoothly.
• Select the appropriate packing material and specifications: Based on the valve's working environment, media characteristics, temperature, pressure, and other factors, choose the appropriate packing material and specifications. Common packing materials include graphite, polytetrafluoroethylene (PTFE), and flexible graphite. Each type of packing material has its applicable range and characteristics. For example, graphite packing has good high-temperature resistance and chemical stability, making it suitable for valves handling high-temperature, high-pressure, and highly corrosive media. In contrast, PTFE packing has a low friction coefficient and good self-lubricating properties, making it suitable for valves handling low-temperature, low-pressure, and mildly corrosive media.
• Pay attention to the sealing and tightening of the packing during installation: When installing new packing, ensure its sealing and tightening. Place the packing into the packing gland in a circular manner, and after each circle of packing is placed, gently tighten it with the packing gland cover to ensure the packing fits snugly. The installation position of the packing should be correct, without any tilting or loosening. Finally, tighten the packing with the packing gland cover, but be careful not to overtighten or undertighten. Overtightening can overly compress the packing, making valve stem movement difficult and potentially damaging the valve stem. Undertightening, on the other hand, cannot guarantee sealing effectiveness and is prone to leakage.

Through the above methods, we can accurately determine whether the valve packing gland needs packing replacement. In actual work, these methods should be comprehensively applied according to specific situations to promptly identify packing issues and replace them, ensuring the normal operation and sealing performance of the valve. At the same time, when replacing packing, it is essential to strictly follow the operating procedures, select the appropriate packing material and specifications, and pay attention to the details during the installation process. Only in this way can we ensure that the valve will operate reliably in subsequent use, avoiding safety accidents and production failures caused by packing problems.