1, different types and brands of hydraulic oil can not be mixed to prevent chemical reaction, its performance changes will appear dark brown, milky white, odor hydraulic oil belongs to metamorphic oil, so it can not be used. two。. Use qualified hydraulic oil filter element to prevent solid impurities in the filter element from mixing into the hydraulic system. Clean hydraulic oil is the life of the hydraulic system. There are many precision couple parts in the hydraulic system, some with gaps and some with damping holes. If the invasion of solid impurities will lead to the pull of precision couple parts, hair card, oil road blockage and so on, it will endanger the safe operation of the hydraulic system. 3. The ways for solid impurities to invade the hydraulic system are as follows: unclean hydraulic oil, unclean refueling tools, careless refueling and maintenance, shedding of hydraulic components, and so on. Finally, pay attention to prevent air and water from seeping into the hydraulic system.