(1) makes the oil have certain compressibility, which makes the system produce noise, vibration and crawling of moving parts, which destroys the stability of the work;

(2) It is easy to make the oil oxidized and deteriorate, and reduce the service life of the oil.

Solution:

1, there are more opportunities for air to enter the system from the oil tank, such as insufficient oil in the oil tank; Hydraulic pump oil suction pipe invades the oil too short; The distance between the oil suction pipe and the oil return pipe in the oil tank is too close or not separated by a partition; The return oil splashes and is stirred into foam; Hydraulic pump sucks air; The oil return pipe is not inserted into the oil tank, so that the return oil rushes out of the oil surface and the tank wall, and a large number of bubbles are generated on the oil surface, so that air and oil are sucked into the system together. Therefore, the oil level of the fuel tank should always be kept high enough; The oil suction pipe and oil return pipe shall be kept below the minimum oil level and separated by partitions;

2. Because the seal is not tight or the screw at the joint between the pipe joint and the hydraulic component is not tightened, the outside air will invade from these places; The parts below atmospheric pressure in the system, such as oil suction cavity, oil suction pipe and local areas with high oil velocity (low pressure) in the oil pressure pipe of hydraulic pump; When the system stops working and the oil in the oil return cavity in the system returns to the oil tank through the oil return pipe, a local vacuum zone will also be formed, and air is the easiest to invade. Therefore, we should try to prevent the pressure everywhere from being lower than atmospheric pressure; All sealing parts should use good sealing devices, and the screws at the pipe joints and joint surfaces should be tightened; Always clean the filter at the oil suction port of the hydraulic pump to prevent the air dissolved in the oil from entering the system due to the increase of oil suction resistance;

3. For the main hydraulic equipment, it is best to have an exhaust device on the hydraulic cylinder to eliminate the air in the system.