The slight gas seepage observed in the manhole gasket is due to leakage gaps that have always existed in the seal itself; it is not a sudden leak that occurs only in the late stages of concentration. Rather, under the operating conditions in the early stages, the impact of the gas seepage was masked. As concentration progresses to the later stages, changes in the material and vapor phase loads cause the abnormalities resulting from the leakage to become fully apparent. During the early stages of evaporation, the feed concentration is low, steam production is high, and the vapor flow rate inside the evaporation chamber is sufficient, with a large volume of secondary steam continuously flowing upward. The small amount of air seeping in at the manhole is entrained by the high-volume steam flow and is directly extracted by the vacuum pump via the exhaust line. The entrained non-condensable air is rapidly diluted and carried away, insufficient to accumulate inside the chamber. It has virtually no discernible effect on the vacuum, and both instrument readings and process conditions appear normal, making it difficult to detect the micro-leakage at the site. As concentration continues, the salt concentration of the feed solution rises, the boiling point of the feed increases, the amount of secondary steam generated per unit time decreases significantly, and the total gas flow rate is drastically reduced. For a leak of the same size, the total volume of air entering remains unchanged, but the steam’s dilution capacity weakens, causing non-condensable gases to begin accumulating inside the chamber. These non-condensable gases occupy the heat exchange space, raising the chamber’s actual pressure. This manifests as a drop in vacuum level; even if the vacuum pump itself is operating normally, the vacuum cannot reach the levels achieved earlier, and failure symptoms thus become apparent. Toward the end of the concentration process, the liquid level in the chamber drops, and the environmental conditions around the manhole flange also change. Early in the concentration process, when the liquid level is high, the flange sealing surface is continuously wetted by steam and some material mist. The gaps in the gasket are temporarily sealed by a liquid film formed by water vapor and salt mist, which acts like a water seal and, to some extent, blocks gas from seeping inward. In the later stages, as the liquid level drops and the foam in the feed solution decreases, the gasket is no longer moistened by water vapor. The temporary liquid film in the gaps disappears, and the leakage pathways that were previously blocked by the film open completely, resulting in a further increase in actual gas leakage compared to the early stages. The alternating thermal cycles also cause cumulative aging of the gasket over time. As the seal repeatedly undergoes cycles of heating, cooling, compression, and rebound, the seal material gradually hardens and develops microcracks, causing leakage pathways to form over time. In the early stages of operation, the gaps are minute and masked by the high steam flow rate. However, as batches continue to run, the cracks slowly widen. By the time each batch reaches the final stage of concentration, the combined effects of these factors lead to a concentrated outbreak of process abnormalities caused by leakage. There are also symptoms caused by process interlocks: during the late stages of concentration, the system itself is far more sensitive to changes in vacuum than during the initial feed stage. High-concentration brine is highly sensitive to vacuum; even minor vacuum fluctuations can directly result in increased evaporation temperatures, intensified foaming, and carryover or material loss. During the early stage of processing dilute feed, vacuum fluctuations of the same magnitude produce virtually no detectable changes in the process and do not attract the attention of operators. In many on-site maintenance inspections, upon disassembly, the gaskets show no obvious damage or fractures—only fine hairline cracks. After replacing the gaskets, the instability in vacuum during the late stages of each batch disappears immediately. This type of failure is easily misdiagnosed as insufficient vacuum pump capacity, leading to the oversight of micro-seepage issues at flanges such as manhole flanges. In short, the leak has always been present. In the early stages, high steam flow and a temporary liquid film seal masked the problem; later, as steam flow decreased, the liquid film disappeared, and the material became sensitive to vacuum, the consequences of the minute gas leakage became fully apparent.