Аннотация
Purpose. To identify and quantify the main factors causing failures in hydraulic systems of open-pit excavators, with particular emphasis on the influence of the cleanliness and physicochemical condition of the working fluid on the reliability and service life of hydraulic units. Methods. The study is based on an integrated approach that includes an analytical generalization of literature and operational data on hydraulic system failures, determination of working fluid cleanliness class using a Luvatech S41 particle counter, and physicochemical characterization of fluids by infrared spectroscopy, X-ray fluorescence analysis, visual assessment, and microscopy. The effect of contamination on the service life of hydraulic units was additionally evaluated using a calculation model that accounts for particle concentration and particle-size distribution. Findings. It was established that working fluid contamination accounts for approximately 70% of hydraulic system failures. Particle count analysis showed a progressive increase in contamination with increasing operating time, with the most pronounced growth observed for the 2-5 and 5-10 μm fractions, indicating intensified abrasive wear in the hydraulic system. X-ray fluorescence analysis revealed an increase in SiO2 content from 88.740 to 93.474%, indicating contamination of the working fluid by silicon-bearing abrasive particles. Infrared spectroscopy identified structural changes in the working fluid and the appearance of additional absorption bands associated with its chemical degradation during operation. Microscopic examination of used oil confirmed the presence of solid impurities. An economically and technically justified working fluid cleanliness level corresponding to ISO 4406 class 15/13 was determined, thereby improving reliability and reducing operating costs. Originality. For the first time, an integrated approach is applied, combining particle-size analysis, physicochemical diagnostics of the working fluid, and assessment of hydraulic unit life to establish the relationship between working-fluid cleanliness, contamination characteristics, and hydraulic-system reliability under real operating conditions. Practical implications. The results obtained can be used to improve filtration systems, optimize maintenance strategies, and support early diagnostics and predictive maintenance of hydraulic equipment at mining enterprises.