Thread Content
Among industrial automation instruments, control valves are considered bulky, and due to their simple structure, they often do not receive much attention. However, it is located on the process pipelines, in complex working conditions; once a problem arises, everyone gets busy trying to deal with it. Due to its bulkiness, it is difficult to identify the problems; it often requires considerable effort with little reward, and it also involves issues such as system operation, system integrity, control quality, and environmental pollution. Cleaning method: Common faults include slag, rust, and debris in the pipelines causing blockages or jams at the throttle ports, guide areas, and balance holes on the lower valve cover; this can result in scratches and damage to the surface of the valve core and its 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. In such cases, it is necessary to disassemble the component for cleaning in order to remove debris. If the sealing surface is damaged, it must be ground as well. At the same time, the plug should be removed to flush out any debris that has fallen into the lower valve cover from the balance hole, and the pipelines should also be cleaned. Before putting it into operation, open the control valve fully; allow the medium to flow for a while before proceeding with normal operation. External flushing method: When using ordinary valves to regulate media that tend to precipitate and contain solid particles, blockages often occur at the throttling points and guide areas; in such cases, flushing gas and steam can be introduced 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. Pipeline 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 blockage, it is best to install a filter on the pipeline before 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. 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. Medium scouring method: Utilizes the scouring energy of the medium itself to wash away and remove substances that tend to settle or cause blockages, thereby enhancing the valve’s resistance to blockage. Common methods include: converting it to a flow-closed design; using a streamlined valve body; placing the throttle opening in the area most subject to erosion. When using this method, it is important to enhance the erosion resistance of the material used for the throttle components. Changing from straight-through to angular flow: The straight-through configuration results in an inverted S-shaped flow pattern; the flow path is complex, with numerous dead zones in the upper and lower chambers, which provide areas where the medium can settle. Angular connection: the medium flows as if through a 90° elbow, offering good scouring performance, a small dead zone, and allowing for easy design in a streamlined shape. Therefore, when a slight blockage occurs with a straight-through control valve, it can be replaced with an angle valve.