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Sealing Technology of Hydraulic Valve and Its Analysis
Hydraulic support valves suffer from a short service life, and although foreign solutions have focused on improving filtration accuracy and emulsion quality, the results have been limited. This article explores the development of the sealing pair in the holder valve, examining the relationship between the material of the seal and its performance. It emphasizes that sealing technology is key to extending the lifespan of hydraulic valves in hydraulic supports.
Hydraulic supports are critical components in coal mining machinery, designed to last up to five years after overhaul. However, the service life of individual hydraulic valves within these systems is often very short—sometimes only a few weeks or a few months. Foreign approaches have tried to address this by enhancing filtration systems and improving emulsion quality, but with little success. For example, a British hydraulic valve, despite high processing precision and filtration standards, has struggled due to its low durability, leading to its potential elimination in certain markets.
A major factor affecting the sealing performance of hydraulic valves is contamination in the working fluid. Impurities in the oil can cause abrasive wear between sealing elements, leading to leaks. Therefore, foreign manufacturers recommend using filters with appropriate accuracy. They argue that 5μm seals paired with 3μm filters can extend the life of the system tenfold compared to 10μm filters. However, in hydraulic support systems, the working environment is extremely harsh. The pipelines can exceed 1,000 meters in length, with over 4,000 connectors, and there are no special dust-proof measures in place. Emulsions often contain significant amounts of floating impurities, including coal dust, rock particles, and iron filings, which accumulate in the cylinder and valve cavities.
The intake valve plug and seat, which open and close frequently and experience high liquid flow, tend to fail quickly. Reducing contamination in such a system has proven extremely challenging. Some attempts have included installing high-pressure filters at the emulsion pumping station and small filters at each support’s inlet, but these were quickly clogged during operation, causing downtime.
With the advancement of hydraulic support technology, the demand for better valve performance and longer life has increased. Currently, valve life is tested using the total flow of emulsion through the valve and the number of opening and closing cycles, with a 120-mesh filter and magnetic filtration. However, there is a significant gap between indoor testing and real underground conditions. Many countries now include anti-pollution requirements in formal tests, sometimes introducing pulverized coal or mechanical impurities into the emulsion. To address these challenges, new sealing materials with improved pollution resistance and adaptability to underground conditions are urgently needed.
The history of hydraulic valve seal materials shows that early hydraulic supports used metal-to-metal contact seals without additional sealing layers. These required high precision in surface matching or relied on plastic deformation to block leak paths. Over time, more advanced sealing materials have been developed to improve reliability and longevity in harsh environments.