Maintenance of the hydraulic system of construction machinery is critical for hydraulic transmission construction machinery, and the hydraulic system’s regular operation is a key indicator of its good technical condition. Qualified hydraulic oil is the assurance of a hydraulic system’s dependable operation, and proper maintenance is the cornerstone of a hydraulic system’s reliable operation. To that purpose, we will give a brief overview of the maintenance of the hydraulic system of construction machinery in the general working environment, as per our work practice.
Choose the right hydraulic oil
Hydraulic oil functions in the hydraulic system by conveying pressure, lubricating, cooling, and sealing. The main cause of early hydraulic system failure and durability reduction is incorrect hydraulic oil selection. The hydraulic oil should be chosen in accordance with the machine’s “Instruction Manual” specifications. When a different hydraulic oil is required in unusual conditions, it should operate similarly to the required hydraulic oil. To avoid chemical interactions and changes in hydraulic oil performance, different hydraulic oils cannot be blended. Hydraulic oil that is dark brown, milky white, and odorous is degrading and should not be utilized.
Prevent solid impurities from mixing into the hydraulic system
A hydraulic system’s life is dependent on clean hydraulic oil. The hydraulic system contains several precise pieces, some of which have dampening holes, gaps, and other features. If solid impurities enter, the precise coupler will be pulled, the card will be issued, the oil route will be restricted, and the hydraulic system’s safe functioning would be jeopardized. Filthy hydraulic oil; unclean refueling equipment; negligent refueling and repair and maintenance; hydraulic component desquamation, and so on are all common ways for solid contaminants to enter the hydraulic system. The following factors can help prevent solid contaminants from entering the system:
Filtered hydraulic oil must be filled, and the filling tool must be clean and dependable. To boost the pace of refueling, do not remove the filter from the filler neck of the gasoline tank. To avoid solid and fibrous contaminants from slipping into the oil, refueling staff should wear clean gloves and overalls.
To eliminate dust when the system’s oil passage is exposed, remove the hydraulic oil tank filling cap, filter cover, inspection hole, hydraulic oil pipe, and other parts, and carefully clean the dismantled parts before opening. When removing the oil filler cap of a hydraulic oil tank, for example, first remove the soil around the oil tank cap, then loosen the oil tank cap, remove the debris remaining in the joint (do not rinse with water to avoid water infiltration), and open the oil tank cap after confirming that it is clean. Wiping materials that do not remove fiber contaminants and special hammers with rubber attached to the striking surface should be used when wiping materials and hammers are required. Before assembly, hydraulic components and hydraulic hoses should be thoroughly cleaned and dried with high-pressure air. Select a genuine filter element that is well-packaged (the inner package is damaged, although the filter element is intact, it may be unclean). Clean the filter at the same time as you change the oil. Clean the dirt from the bottom of the filter housing using a cleaning material before inserting the filter element.
Cleaning of the hydraulic system
The cleaning oil must be the same grade as the hydraulic oil in the system, the temperature of the oil should be between 45 and 80 °C, and the pollutants in the system should be removed as much as possible with a high flow rate. It is recommended that the hydraulic system be cleaned at least three times. All of the oil should be discharged from the system while it is still hot after each cleaning. Clean the filter after cleaning, replace the new filter element, and apply new oil.
Prevent air and water from invading the hydraulic system
Prevent air from invading the hydraulic system
The hydraulic oil contains air with a volume ratio of 6 to 8% under normal pressure and temperature. The air will be liberated from the oil as the pressure is dropped, and the bubble will burst, causing the hydraulic components to “cavitate” and make noise. A high amount of air entering the oil will exacerbate the “cavitation” phenomena, raise the compressibility of the hydraulic oil, make the work unstable, lower work efficiency, and adversely affect the executive components, such as work “crawling.” Additionally, the air will oxidize the hydraulic oil, hastening its deterioration. The following considerations should be kept in mind to avoid air intrusion:
- After maintenance and oil change, the air in the system must be removed according to the regulations, so that it can work normally.
- The oil suction pipe port of the hydraulic oil pump shall not be exposed to the oil surface, and the oil suction pipe must be well sealed.
- The oil pump’s driving shaft seal should be in good working order. It should be noted that while replacing the oil seal, the authentic “double-lip” oil seal should be used rather than the “single-lip” oil seal, because the “single-lip” oil seal can only seal the oil in one direction and does not have an air sealing function. The hydraulic oil pump on an XCMG zl50 loader made a constant “cavitation” noise when it was serviced, and the oil level in the oil tank automatically increased. After inspecting the hydraulic oil pump repair process, it was discovered that the oil seal on the drive shaft of the hydraulic oil pump had been mislabeled “single lip” due to oil seal.
Prevent water from invading the hydraulic system
Excessive moisture in the oil causes hydraulic component corrosion, oil emulsification and degradation, lubricating oil film strength loss, and mechanical wear acceleration.