Hydraulic machines were used in both medium and large scale From industries studying problems of hydraulic systems around 70-80 percentage of the machine expiration was due to the deterioration of hydraulic oil from contamination so the best way to maintain the hydraulic machine was to take care of hydraulic oil to have the purity level and other properties suitable for the components in those machines. This article described the duty of hydraulic oil types of contamination sources of contamination the standard for measuring the purity level of oil equipments used to measure and analyze the contamination in hydraulic oil recommended purity levels the effects from the contamination in hydraulic oil to machine and methods to protect and to eliminate the contamination in hydraulic oil. All of these were useful as the guidelines to maintain the hydraulic machines to work in high efficiency and more long life time.

The objective of this research was to study and evaluate of the efficiency of moisture separation from hydraulic oil. This method was conducted by mixing pure water and oil in an oil tank which was classified into 4 cases: 250 ppm. 500 ppm. 750 ppm. and 1000 ppm. The results showed that when the maximum quantity of water was 1000 ppm. the 710 ppm. of moisture could be separated from hydraulic oil. The highest temperature at 70ฐC was utilized when that water was 750 ppm. The maximum efficiency was 80% when the quantity of water was 500 ppm.