How to extend the service life of control valves?

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1 Tips to Extend Service Life 1 I. Operating at Full Opening – Have the control valve operate at its maximum opening from the start, such as 90%. In this way, damages such as gas turbidity and erosion occur on the head of the valve core. As the valve core is damaged, the flow rate increases, causing the valve to close a little more; this process of continuous damage and gradual closing ensures that the entire valve core is utilized to the fullest extent, until the root of the valve core and the sealing surface are damaged and the valve can no longer be used. At the same time, when operating at a large opening, the throttle gap is larger, reducing erosion; this increases the valve’s lifespan by more than 1–5 times compared to operating it at intermediate or small openings from the start. If a chemical plant adopts this method, the service life of the valves is doubled. 2 II. Reducing the valve resistance ratio (or pressure drop ratio) S: By reducing S, the losses in the system other than the control valve increase, which leads to a lower pressure drop across the valve. To ensure that flow can pass through the control valve, it is necessary to increase its opening degree. At the same time, the reduced pressure drop across the valve also decreases the risk of cavitation and erosion. Specific methods include: installing a orifice plate behind the valve to create pressure drop through throttling ； Close the manual valve connected in series on the pipeline until the control valve reaches an optimal operating position. For valves that initially operate at a small opening degree, this method is very simple, convenient, and effective. 3 III. Reducing the diameter and increasing the operating opening: The operating opening can be increased by reducing the diameter of the valve. The specific methods include: ① Replacing the valve with one of a smaller diameter, such as changing from DN32 to DN25 ； ②The valve body remains unchanged; only the valve core and seat with a smaller diameter are replaced. During a major overhaul of a chemical plant, replacing the throttle element dg10 with dg8 doubled its service life. 4. IV. Relocating the areas affected by damage: Move the areas that are severely damaged from critical positions to less important ones, in order to protect the sealing surfaces and throttling surfaces of the valve core and valve seat. It can increase the service life of the valve. 5. V. Changing the flow direction: In the flow-out type, the fluid flows in the direction of the valve core’s opening; cavitation and erosion mainly affect the sealing surfaces, causing rapid damage to the root of the valve core as well as the sealing surfaces of the valve seat ； In the flow-blocking type, flow moves in the direction of closure; cavitation and erosion occur after throttling, below the valve seat sealing surface, which protects the sealing surface and the root of the valve element, thereby extending its lifespan. Note: Even when changing from flow open to flow closed, a jumping phenomenon occurs (when the control valve is opened). The effect of vortices during the adjustment process prevents the control system from making smooth adjustments. This method must be adopted with caution and after comprehensive consideration. 6. VI. Use of special materials: To resist cavitation (damage in the form of honeycomb-like spots) and erosion (streamline-shaped grooves), special materials resistant to cavitation and erosion can be used to manufacture the throttling elements. Such special materials include 6YC—1, A4 steel, stainless steel, and cemented carbide. To resist corrosion, materials that are more resistant to corrosion and possess certain mechanical and physical properties can be used instead. This material is divided into two categories: non-metallic materials (such as rubber, PTFE, ceramics, etc.) and metallic materials (such as Monel, Hastelloy, etc.). 7. VII. Proper selection of valve structure: The lifespan of valves can be increased by altering their structure or by choosing valves with a longer service life, such as labyrinth valves, multi-stage valves, anti-cavitation valves, and corrosion-resistant valves. The advantages of control valves during use are: 1. They respond quickly, enabling them to carry out various adjustment commands in a timely manner ； 2. Used in combination with a large cylinder, it provides a high torque thrust ； 3. It maintains stable performance in harsh working conditions and can operate normally ； 4. High safety performance. The proper functioning and responsiveness of control valves have a direct impact on production quality and efficiency. Therefore, it is particularly important to analyze the factors affecting failures of control valves during use and to develop corresponding solutions.