Valve sealing technology improvements reduce industrial media leakage

Recently, some factories have modified the sealing structure of their pipeline valves, replacing internal seals and valve stem packing. Subsequent leak detection of the modified valves showed a reduction in the number of leaks. This indicates that improvements in valve sealing technology have a practical effect on controlling industrial media leaks.

During valve operation, gaps form between the valve stem and packing. Volatile components in the medium can seep through these gaps. Previously, such minute leaks often went unnoticed. With the widespread availability of leak detection instruments, factories can now locate and address leaking valves. Common solutions include replacing the packing or replacing the entire valve with a bellows-sealed structure.

Bellows-sealed valves use a metal bellows to isolate the valve stem from the medium. The lower end of the bellows connects to the valve stem, and the upper end connects to the valve cover. When the valve stem moves, the bellows expands and contracts, trapping the medium inside and preventing it from contacting the gap between the valve stem and packing. Statistics from a petrochemical company show that replacing some ordinary valves on pipelines with bellows-sealed valves reduced the number of leak detection failures.

Improvements in packing materials have yielded practical results. Early asbestos packing has been phased out. Currently used expanded graphite packing is resilient and maintains a close fit during valve stem movement. PTFE packing is suitable for low-temperature corrosive media and exhibits low frictional resistance. Some manufacturers combine these two materials to create packing rings, which have a longer service life than single-material packing.

The structure of packing glands has also been improved. Traditional glands rely on bolts for fastening, requiring manual tightening after packing compaction. Now, some valves use disc spring-loaded gland structures, where the spring maintains a certain pressure on the packing. As the packing wears, the spring automatically compensates, eliminating the need for frequent manual adjustments. This structure is suitable for pipelines with large temperature fluctuations because the spring provides stable clamping force.

The treatment of internal valve sealing surfaces is also changing. Friction occurs between the valve disc and seat during opening and closing. When the medium contains impurities, scratches easily appear on the sealing surface, leading to incomplete valve closure. To address this issue, many valves have hard alloys, such as cobalt-based or nickel-based alloys, welded onto the sealing surface to increase surface hardness. For severely worn applications, supersonic flame spraying technology is used to apply tungsten carbide powder to the sealing surface to form a coating. Valves using this process can maintain an effective sealing time for longer periods in media such as coal slurry and mineral slurry.

Improved valve manufacturing precision also contributes to improved sealing performance. Modern valve processing utilizes CNC machine tools, controlling the roundness, roughness, and straightness of the valve body sealing surface and valve stem. Increased precision means a smaller initial clearance, providing a foundation for long-term sealing. Pre-shipment testing methods are also being improved. In addition to hydrostatic sealing tests, low-pressure gas sealing tests have become a specified requirement for many users. Under low-pressure conditions, defects on the sealing surface are more easily exposed.

Intelligent monitoring technology is beginning to be applied to valve sealing management. Some valves integrate leakage sensors in the stuffing box. When the sensor detects gas or liquid, it sends a signal, which the control room can then detect. The internal sealing status is assessed by analyzing the torque or stroke data of the actuator. When abnormal fluctuations occur in the valve closing torque, it may indicate that impurities are stuck or damaged on the sealing surface, and the system will prompt maintenance personnel to inspect it.