We often learn from user feedback that many valves encounter various issues in practical applications. Some problems stem from the packing material, while others are due to manufacturing defects or design flaws. Additionally, wear caused by the frequency of temperature changes and switching operations can also be a significant factor.
For instance, when we communicated with the maintenance department of Sinopec in Guangdong, they reported that the actual leakage values on-site were much higher than the required 200-500 PPM, often ranging from 5,000 to 10,000 PPM. Their maintenance approach involved applying grease and increasing the pre-tension of the jacking bolts, but this solution was only effective for about a week before the leakage exceeded the standard again, necessitating repeated maintenance efforts.
Subsequently, the petrochemical plant brought over a dozen brand-new valves to our factory for low-emission modifications. During the modification process, we found that many details of the valves were not up to standard, including significant variations in the packing gland dimensions of valves of the same specification and the surface finish of the valves. These issues are among the main causes of excessive on-site leakage.
Many valve manufacturers only pay attention to the valves sent for inspection when customers specify low-emission requirements, without delving into detailed design and process improvements. For example, when it comes to ISO 15848 Part 5 with 5 cycles and ISO 15848-1 with 205 cycles, many ordinary processes can meet the ISO 15848 Part 5 standard with just 5 cycles. However, as the valves are stored for longer periods, the stress in the graphite packing rings is released again, leading to sticking issues. When the valves are opened again, the graphite packing rings can be damaged internally, causing excessive leakage.
In the case of low-temperature ball valves, many factory engineers do not understand the mechanical principles of packing rings and have not conducted sufficient experimental verification. They simply focus on reducing the operating torque in the design, using V-shaped graphite for linear sealing. However, once these valves are installed in the field and subjected to temperature changes and frequent switching, the stress in the V-shaped area diminishes, leading to leakage issues that cannot be resealed.
Many ball valves use anti-explosion sealing O-rings, but most O-ring manufacturers only achieve hardness without toughness. As a result, under high pressure without a retaining ring, these O-rings can be extruded and torn. The vulcanization process for anti-explosion O-rings requires low-temperature and long-duration operations. If the temperature is too high, the rubber does not fully cross-link before vulcanization, creating an illusion of sufficient hardness and explosion resistance. Consequently, valve quality inspectors only use hardness tests for acceptance.
In high-temperature power plants operating at 560 degrees Celsius, it is common to encounter issues with valve stem corrosion, leading to difficulties in opening the valves. This is because many valve manufacturers mistakenly believe that low-leakage packing is better, without realizing that the fluorine content in the graphite packing can break down into free ions at high temperatures, forming hydrofluoric acid that severely corrodes the valve stem.
In the case of many hard-sealed ball valves, we often hear from industry insiders that factory pressure tests are qualified, but after some time, when customers conduct acceptance pressure tests, the valves fail due to leakage. This is because many engineers do not truly understand the relationship between the spring force in the valves and the rebound force of the graphite. In many initial states, the valves leak, but when water pressure is applied, the water expands the volume of the graphite, making the valves appear qualified during air pressure tests. After some time, when the moisture in the graphite evaporates and the volume contracts back to its original state, the spring force is no longer sufficient to deform the graphite, leading to leakage during subsequent pressure tests. Many designers mistakenly believe that the graphite is not thick or wide enough and continue to head in the wrong direction.
Therefore, when addressing industry issues, we focus more on material science and tribology to identify the core problems and first resolve the fundamental issues of the products.