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1. The choice of hydraulic system oil, hydraulic oil should meet the following requirements:

It should not contain steam, air and other impurities which are easy to be gasified and produce gasification; It has good lubrication performance and high liquid film strength; It has high chemical stability; appropriate viscosity and good viscosity-temperature properties.

2. Harm and prevention measures of hydraulic system oil pollution hydraulic system pollution is a major cause of hydraulic failure. After the contamination is mixed into the system, it will accelerate the abrasion, grinding loss, burn and even damage of hydraulic parts, or cause the valve action failure or noise. Pollutants will block the throttle hole or throttle gap of hydraulic components, change the working performance of the hydraulic system, cause maladjustment or even complete failure, and cause misoperation and accidents. Dust particles in the hydraulic cylinder will accelerate the damage of seals, and the strain on the inner surface of cylinder drum will increase leakage, insufficient thrust or unstable movement, crawling and speed decline, resulting in abnormal sound and vibration. Therefore, management must be strengthened to prevent oil pollution and ensure safe and reliable operation of the hydraulic system.

3. Harm and prevention measures of air entering the hydraulic system the compressibility of oil used in the hydraulic system is very small, but the compressibility of low-pressure air is very large, which is about 10,000 times that of oil, even if the system contains a small amount of air, it has a great influence and will cause system failure. (1) the harm of air entering the hydraulic system. (2) measures to prevent air from entering the hydraulic system. According to the different reasons why air enters the hydraulic system.