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I. Methods to prevent clogging (sticking) of control valves (6 methods) 1. Cleaning method: Weld slag, rust, debris, etc. in the pipeline can cause blockages or sticking at the throttle ports, guide areas, and balance holes on the lower valve cover, leading to scratches and abrasions on the valve core’s surface and guide surfaces, as well as indentations on the sealing surfaces. This often occurs in newly commissioned systems and in the early stages after major repairs. This is the most common fault. In such cases, it is necessary to remove the component for cleaning in order to get rid of debris; if the sealing surface is damaged, it should also be ground ； At the same time, open the bottom plug to flush out the debris that has fallen from the balance hole into the lower valve cover, and to clean the piping. Before putting it into operation, open the control valve fully; allow the medium to flow for a while before proceeding with normal operation. 2. External flushing method: For media that tend to precipitate and contain solid particles, when using ordinary valves for regulation, blockages often occur at the throttling points and guide areas; in such cases, flushing gas and steam can be supplied at the bottom plug of the lower valve cover. When the valve becomes clogged or stuck, opening the external gas or steam valve allows for flushing to be carried out without moving the control valve, thereby restoring normal operation of the valve. 3. Pipe filter installation method: For small-diameter control valves, especially those with extremely low flow rates, the throttling gap is very small; therefore, there must not be any debris in the fluid. In the event of such blockages, it is best to install a filter on the pipeline ahead of the valve to ensure smooth flow of the medium. For control valves used with positioners, when the positioner does not function properly, the most common fault is a blocked throttle in its air supply line. Therefore, when the locator is in use, the air supply must be properly managed; the common approach is to install an air filter and pressure reducing valve on the air supply pipeline before the locator. 4. The method of increasing the throttling gap: When solid particles in the medium, or welding slag and rust that have been washed away in the pipes, cause blockages or jams due to their inability to pass through the throttling opening, it is possible to use throttling elements with a larger throttling gap – valve cores or sleeves with window-like or open-shaped throttling areas. Since the throttling area is concentrated rather than distributed circumferentially, such problems can be easily resolved. For single or double-seat valves, the plunger-type valve core can be replaced with a valve core having a “V”-shaped port, or it can be changed to a cartridge valve or similar. For example, a chemical plant had a two-seat valve that would get stuck frequently; after it was recommended to switch to a sleeve valve, the problem was resolved immediately. 5. Medium scouring method: This method makes use of the scouring energy of the medium itself to scour away and remove substances that tend to settle or cause blockages, thereby enhancing the valve’s resistance to blockages. Common methods include: ① Modifying it for use in a flow-closed configuration ； ②Use a streamlined valve body ； ③Place the throttle at the area most subject to erosion; when using this method, it is important to improve the erosion resistance of the material used for the throttle component. 6. Changing from straight-through to angular flow method: The straight-through configuration involves an inverted S-shaped flow pattern, resulting in a complex flow path and numerous dead zones in the upper and lower chambers, which provide areas for the deposition of the medium. Angular connection: the medium flows as if through a 90-degree elbow, resulting in good scouring performance, a small dead zone, and ease of designing it into a streamlined shape. Therefore, when a slight blockage occurs with a straight-through control valve, it can be replaced with an angle valve for use. II. Solutions for poor sealing performance (5 methods) 1. Grinding method: Perform fine grinding to remove marks, reduce or eliminate the sealing gap, and improve the smoothness of the sealing surface in order to enhance sealing performance. 2. The method of increasing the sealing specific pressure using unbalanced forces: When the actuator exerts a constant sealing pressure on the valve core, and unbalanced forces try to push the valve core apart, the sealing force on the valve core is the result of subtracting these two forces from each other. Conversely, if the unbalanced forces try to push the valve core together, the sealing force is the result of adding these two forces together. This approach **increases the sealing specific pressure, and the sealing efficiency can be improved by 5 to 10 times or more compared to the previous method. Valves with a single seal and a dg value of 20 or higher generally fall into the first category; they are usually of the flow-open type. If the sealing performance is not satisfactory, changing them to a flow-close type will result in a significant improvement in sealing performance. This is especially true for two-position on/off control valves, which should generally be used in flow-close mode. 3. Increasing the sealing force of the actuator: Raising the sealing force of the actuator on the valve core is also a common method to ensure that the valve remains closed, by increasing the sealing pressure and thereby enhancing the sealing performance. Common methods include: ① Moving the spring’s operating range ； ②Switch to a spring with lower stiffness ； ③Add attachments, such as those with locators ； ④Increase gas source pressure ； ⑤Switch to an actuator with greater thrust. 4. Use single-seal or soft-seal methods. For control valves that originally use double sealing, a single seal can be adopted, which usually improves the sealing effect by more than 10 times. If the unbalanced forces are significant, additional measures should be taken. For valves with hard seals, switching to a soft seal can also enhance the sealing effect by more than 10 times. 5. Use valves with better sealing performance. As a last resort, it is possible to consider using valves that offer improved sealing properties. For example, ordinary butterfly valves can be replaced with elliptical butterfly valves; further, cut-off butterfly valves, eccentric rotary valves, ball valves, and specially designed cut-off valves can also be used. III. Solutions to leakage in control valves (6 methods) 1. Adding sealing grease: For valves that do not currently use sealing grease, it is possible to add such grease to improve the sealing performance of the valve stem. 2. Adding packing: To improve the sealing performance of the packing around the valve stem, the method of adding more packing can be employed. Usually, a dual-layer or multi-layer mixed packing structure is used; simply increasing the number of elements, for example from 3 to 5, does not yield significant results. 3. Graphite packing replacement method: The widely used PTFE packing has an operating temperature range of –20 to +200°C; when the temperature fluctuates significantly within these limits, its sealing performance deteriorates markedly, it ages quickly, and its lifespan is short. Flexible graphite fillers can overcome these disadvantages and have a long service life. As a result, some factories have replaced all PTFE packing with graphite packing, and even newly purchased control valves have their PTFE packing replaced with graphite packing before being put into use. However, the hysteresis is large when using graphite fillers, and some systems even exhibit crawling behavior at first; this must be taken into consideration. ℃ 4. Change the flow direction, placing P2 at the valve stem end. When △P is large and P1 is also high, sealing P1 is clearly more difficult than sealing P2. Therefore, the flow direction can be changed so that P1 is located at the valve stem end while P2 is at the other end; this approach is effective for valves with high pressures and large pressure differences. For example, in bellows valves, it is usually necessary to consider sealing P2. 5. The lens gasket sealing method is used for sealing the upper and lower covers, as well as for sealing the valve seat to the upper and lower valve bodies. In the case of flat-seal designs, the sealing performance is poor under high temperature and pressure, leading to leaks; using a lens gasket sealing method can yield satisfactory results. 6. Replacing gaskets: To this day, most gaskets are still made of asbestos sheets; under high temperatures, their sealing performance is poor and their lifespan is short, which leads to leaks. In such cases, wound gaskets or \"O\"-rings can be used as alternatives; many factories are now adopting them. IV. Solutions to Vibration of Control Valves 1. The method of increasing stiffness: For oscillations and mild vibrations, increasing the stiffness can be used to eliminate or reduce them; methods such as using springs with higher stiffness or switching to piston actuators are feasible. 2. The method of increasing damping: Increasing damping means increasing the friction against vibrations; for example, the plug of a sleeve valve can be sealed using an “O”-ring, or graphite packing with high friction can be employed. This can help to eliminate or reduce minor vibrations to some extent. 3. The method of increasing the guiding dimensions and reducing the clearance between components: Axial plug valves generally have small guiding dimensions, and the clearance between their components is usually large, ranging from 0.4 to 1 mm; this condition facilitates the occurrence of mechanical vibrations. Therefore, when mild mechanical vibrations occur, these vibrations can be reduced by increasing the guiding dimensions and decreasing the clearance between the components. 4. The method of changing the shape of the throttling element to eliminate resonance: Since the so-called source of vibration in control valves lies at the throttling area where flow is rapid and pressure changes sharply, altering the shape of the throttling element can change the frequency of this vibration source, making it easier to resolve the issue when resonance is not severe. The specific method is to turn the valve core surface by 0.5–1.0 mm within the vibration opening range. In a factory residential area, a self-acting pressure control valve was installed; resonance caused humming noise that disturbed the workers’ rest. By grinding 0.5 mm off the surface of the valve core, the resonant humming noise disappeared. 5. Method of eliminating resonance by replacing the throttle element: The principle is the same as that in 4) of 4.5, except that the throttle element is replaced. The methods include: ① Changing the flow characteristic, from logarithmic to linear, or from linear to logarithmic ； ②Change the type of valve core. If the plug type is changed to a “V”-groove valve spool, and the double-seat valve plug type is changed to a cartridge type ； Replace the sleeve with openings with a sleeve featuring small holes, etc. For example, in a nitrogen fertilizer plant, a DN25 two-seat valve experienced frequent breakage at the connection between the valve stem and the valve core; after identifying resonance as the cause, we replaced the linear-characteristic valve core with a logarithmic one, and the problem was resolved. Another example is a DN200 sleeve valve used in a laboratory at an aviation academy, whose plug suffered from severe rotation and could not be used properly; by replacing the sleeve with openings with a sleeve featuring small holes, the rotation stopped immediately. 6. Replace the type of control valve to eliminate resonance. Control valves with different structural designs have distinct natural frequencies; replacing the type of control valve is the most effective way to eliminate resonance fundamentally. A valve that experiences severe vibration – intense shaking (which can even damage the valve in extreme cases), strong rotation (to the point where the valve stem may break or twist), and produces loud noise (reaching over 100 decibels) – will see immediate improvement once it is replaced with a valve that has a significantly different structure; the severe resonance disappears miraculously. In the new expansion project of a vinylon plant, a DN200 sleeve valve was selected; all three of the aforementioned problems occurred. The DN300 pipeline would vibrate, the valve plug would rotate, and the noise level reached over 100 decibels. The resonance occurred at an opening degree of 20–70%. Given the large resonance opening degree, a double-seat valve was used instead, and as a result, the resonance disappeared and the valve operated normally. 7. Method of reducing cavitation vibration: For the cavitation vibration caused by the rupture of cavitation bubbles, it is natural to seek ways to reduce cavitation. ①Ensure that the impact energy generated by the bursting of bubbles does not act on the solid surface, especially the valve core, but is absorbed by the liquid instead. Sleeve valves possess this feature, which allows the plug-type valve core to be replaced with a sleeve-type one. ②All methods to reduce cavitation should be employed, such as increasing throttling resistance, raising the pressure at the constriction, and using staged or series decompression. 8. Avoid vibration caused by external shock waves. External shock waves can cause vibration in the valve, and this is something that must be avoided during the normal operation of control valves; if such vibration occurs, appropriate measures should be taken.