The adverse consequences of air intrusion into the hydraulic system of construction machinery mainly include:

　　(1) The oil has a certain compressibility, which causes the system to produce noise, vibration, and cause the moving parts to crawl, and destroys the stability of the work;

　　(2) Easy to oxidize and deteriorate the oil, reducing its service life.

　　Solution: 1. There are more opportunities for air to enter the system from the fuel tank, such as insufficient fuel in the fuel tank; The suction pipe of the hydraulic pump is too short when it enters the oil; The distance between the suction pipe and the return pipe in the fuel tank is too close or not separated by a partition; The return oil splashes and stirs into foam; Hydraulic pump sucks in air; The return oil pipe is not inserted into the oil tank, causing the return oil to flush out of the oil surface and tank wall. A large number of bubbles will be generated on the oil surface, causing air and oil to be sucked into the system together. Therefore, the oil level of the fuel tank should always be maintained at a sufficient height; The suction pipe and return pipe should be kept below the lowest oil level, and the two should be separated by partitions;

　　2. Due to poor sealing or loose screws at the joint of the pipe and hydraulic components, external air will invade from these places; The parts of the system that are below atmospheric pressure, such as the suction chamber of the hydraulic pump, the suction pipe, and the local areas in the pressure pipe where the oil flow velocity is high (low pressure); When the system stops working and the oil in the return chamber returns to the fuel tank through the return pipe, local vacuum areas will also be formed, where air is most likely to invade. Therefore, it is necessary to try to prevent the pressure in various places from being lower than atmospheric pressure; All sealing components should use good sealing devices, and the screws at the pipe joints and joint surfaces should be tightened; Regularly clean the filter at the oil suction port of the hydraulic pump to prevent the increase of oil suction resistance from liberating the air dissolved in the oil and entering the system;

　　3. For major hydraulic equipment, it is best to have an exhaust device on the hydraulic cylinder to remove air from the system.