Active control of hydraulic oil contamination to extend the service life of aviation hydraulic system

The hydraulic system is the control center of aircraft, the performance of which is critically dependent on the purity of the oil that flows through it. Contamination of hydraulic system oil has been known to be the primary cause of catastrophic failure and accidents. A review of literature in the area of hydraulic oil contamination reveals three facts: (i) there is a dearth of effective methods to prevent intrusion of external contaminants into the hydraulic oil, (ii) there are no effective purification methods for liquid and gaseous contaminants of oil, and (iii) there is an absence of real-time monitoring for major contaminants. This work systematically reviews the hazards, sources, and removal methods of major contaminants, especially of gaseous contaminants. An active method to control oil contamination is proposed instead of the existing passive maintenance techniques that are ridden with problems. In a case study of aviation hydraulic system, our active control system comprises (i) a closed hydraulic circuit and a closed oil tank to prevent the intrusion of external contaminants, (ii) a vacuum centrifuge to efficiently remove contaminants without creating consumption costs, and (iii) monitoring devices installed to actively monitor the contaminant content in oil during operation. The results from the purification experiments and three-dimensional modeling indicate that the active control of hydraulic oil contamination can effectively remove 98.4% solid contaminants and reduce the water content below 50 ppm, and in particular reduce the gas content below 2%. It is obvious that this method can improve the continuous operation capability of aviation hydraulic systems and extend the intermaintenance period of aircrafts by reducing the contaminant content in oil.