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Last time, we discussed how to deal with air leakage in the actuator of control valves. Air leakage can cause the control valve to vibrate, but another possible cause of vibration is blockage within the control valve, including blockages in the valve stem and packing, as well as between the valve core and seat, and within the actuator itself. So in this issue, we will discuss how to diagnose and handle issues when using Kasse. 1 Reasons for sticking (1) The sealing packing of the valve stem is compressed too tightly, resulting in increased resistance to the movement of the valve stem. Due to the improved precision of CNC machining, the surface finish of the valve stem is very high. Excessively tight packing increases the resistance between the valve stem and the packing, which causes overshoot when the preloading spring returns to its original position, leading to long-periodic vibrations of the valve (with vibration periods generally exceeding 30 seconds). (2) Using an inappropriate method to adjust the packing gland in a spring-preloaded packing box results in increased operating resistance of the valve stem, as well as damage to the preloading spring or the packing. (3) The low-temperature valve did not use the appropriate packing, resulting in increased frictional resistance. (4) Deformation of the valve stem or misalignment of the packing gland causes the valve stem to rub against the packing gland, resulting in increased operating resistance; this also leads to accelerated wear of the packing and subsequent leakage of the medium. There are usually 2 reasons for stem deformation. ①In positive-acting actuators, the excessive thrust resulting from the gas supply pressure exceeding the valve’s nominal value causes the valve stem to deform. ②Excessive force applied when operating the manual mechanism of the valve caused deformation of the valve stem. (5) Foreign objects get stuck in the stuffing box, increasing the operating resistance of the valve stem. Foreign objects include dust, rust, or rain and snow that are introduced during operation due to unclean valve stems. Furthermore, severe cold leakage from the cryogenic tank or pipelines causes freezing at the valve stem, and the ice then moves through the valve stem into the stuffing box. (6) Blockage inside the valve core, with the main causes including blockage in the guide sleeve section (referred to as oil-free bearings by some manufacturers), crystallization or scaling of the medium inside the valve, and the presence of foreign objects in the valve chamber. Foreign objects are present in the valve chamber due to incomplete purging, equipment corrosion, or the detachment of internal components in pipes or containers. (7) Failure of the actuator mechanism is mainly caused by broken or compressed springs, wear of the teeth in the double-rack actuator, or the loss of components such as the actuator’s limit screws or limit discs. 2. Cassette handling: (1) Keep the valve stem clean and lubricated, and replace the dust seals and guards in a timely manner. (2) Combine with the equipment specialty to prevent ice formation on the valve stem caused by the outward transfer of cooling capacity. (3) Maintain the packing in accordance with the valve operation manual to prevent a decline in its performance. (4) Adjust the air supply pressure according to the factory manuals for the cylinders and valves; do not increase the air supply pressure arbitrarily due to valves not being in place, nor overuse the manual mechanisms. That’s all for this issue. We will regularly update with more tips on industrial control technology – feel free to stay tuned!