1. For the selection of hydraulic system oil, the hydraulic oil shall meet the following requirements:

It should not contain steam, air and other impurities that are easy to gasify and produce gasification; it has good lubrication performance, high liquid film strength, high chemical stability, suitable viscosity and good viscosity temperature performance.

2. Harm and prevention measures of hydraulic system oil pollution hydraulic system pollution is a major cause of hydraulic failure. Pollutants mixed into the system will accelerate the wear, abrasion, burn and even damage of hydraulic parts, or cause valve failure or noise. Pollutants will block the orifices or orifices of hydraulic components, change the working performance of hydraulic system, cause action disorder or even complete failure, resulting in misoperation and accidents. Dust particles in the hydraulic cylinder will accelerate the damage of the seal, the cylinder surface strain, so that the leakage increases, the thrust is insufficient or the action is unstable, crawling, speed drops, produce abnormal sound and vibration. Therefore, management must be strengthened to prevent oil pollution and ensure the safe and reliable operation of the hydraulic system

3. Harm and prevention measures of air entering hydraulic system the compressibility of oil used in hydraulic system is very small, but the compressibility of low-pressure air is very large, which is about 10000 times that of oil. Even if there is a small amount of air in the system, it will have a great influence and cause system failure. (1) Danger of air entering hydraulic system. (2) Measures to prevent air from entering the hydraulic system. According to the different reasons of air entering the hydraulic system.