For mechanized construction enterprises, the good or bad technical condition of construction machinery is a direct factor determining whether the enterprise can maintain normal production. In the case of construction machinery with hydraulic transmission, the proper operation of the hydraulic system is a key indicator of its sound technical condition. Qualified hydraulic oil is the guarantee for the reliable operation of the hydraulic system, and proper maintenance is the foundation for ensuring its dependable performance.

　　Choose the right hydraulic oil.

　　Hydraulic oil plays crucial roles in hydraulic systems, including transmitting pressure, providing lubrication, cooling, and sealing. Inappropriate selection of hydraulic oil is a major cause of early failures and reduced durability in hydraulic systems. Hydraulic oil should be selected according to the grade specified in the accompanying "Operating Manual." In special circumstances where a substitute oil must be used, efforts should be made to ensure that its performance is identical to that of the original grade. Hydraulic oils of different grades must not be mixed, as this could lead to chemical reactions and changes in performance. Hydraulic oil that has turned dark brown, become milky white, or emits an unusual odor is degraded and should not be used.

　　Prevent solid impurities from entering the hydraulic system.

　　Clean hydraulic oil is the lifeblood of a hydraulic system. Hydraulic systems contain numerous precision mating parts, some of which have damping orifices and others have tiny clearances. If solid contaminants enter the system, they can cause damage such as scoring and seizing of precision components, blockage of oil passages, and other issues that jeopardize the safe operation of the hydraulic system. Generally, solid contaminants enter hydraulic systems through the following pathways: unclean hydraulic oil; contaminated refueling tools; careless refueling and maintenance practices; and shedding of debris from hydraulic components. To prevent solid contaminants from entering the system, we can take the following measures: When refueling, hydraulic oil must be filtered before being added, and refueling tools should be thoroughly cleaned and reliable. Under no circumstances should the filter at the oil tank’s fill port be removed simply to speed up the refueling process. Refueling personnel should wear clean gloves and work clothes to avoid letting solid and fibrous contaminants fall into the oil.

　　During maintenance, when removing components such as the hydraulic oil tank filler cap, filter cover, inspection port, and hydraulic hoses, be sure to avoid exposure of the system’s oil passages to airborne dust. Before opening any removed component, thoroughly clean it first. For example, when removing the hydraulic oil tank filler cap, first remove any dirt around the cap’s perimeter. After loosening the cap, carefully clear away any debris remaining at the joint (do not use water to rinse, as this could allow water to seep into the tank). Only open the tank cap after confirming that it is completely clean. If you need to use wiping materials or a hammer, select wiping materials that do not shed fibers and a specialized hammer with a rubber-coated striking surface. Hydraulic components and hydraulic hoses must be carefully cleaned and then dried using high-pressure air before assembly. Use genuine filter elements that are properly packaged (even if the inner packaging is damaged but the filter element itself appears intact, it may still be contaminated). When changing the oil, also clean the filter simultaneously. Before installing the filter element, use wiping materials to thoroughly clean any contaminants from the bottom interior of the filter housing.

　　The cleaning oil used for hydraulic system flushing must be the same grade of hydraulic oil as that already in the system. The oil temperature should be maintained between 45 and 80°C, and a high flow rate should be employed to remove as many impurities as possible from the system. The hydraulic system must be flushed repeatedly at least three times; after each flush, the hot oil should be completely drained from the system while it is still warm. Once the flushing is complete, clean the filters, replace the filter elements with new ones, and then refill the system with fresh oil.

　　Prevent air and water from entering the hydraulic system.

　　Prevent air from entering the hydraulic system.

　　At normal atmospheric pressure and temperature, hydraulic oil contains air at a volume ratio of 6% to 8%. When the pressure drops, this air will separate from the oil, and the bursting of these air bubbles can cause "cavitation" in hydraulic components, resulting in noise. If a large amount of air enters the oil, the cavitation phenomenon will be exacerbated, increasing the compressibility of the hydraulic oil, leading to unstable operation, reduced efficiency, and undesirable effects such as "creeping" in actuating components. Additionally, air can accelerate the oxidation of hydraulic oil, speeding up its degradation. To prevent air from entering the system, pay attention to the following points: 1. After maintenance or oil replacement, be sure to bleed the air out of the system according to the instructions provided in the accompanying "User Manual" before starting normal operations. 2. The suction port of the hydraulic oil pump must not be exposed above the oil level, and the suction line must be tightly sealed. 3. The seal on the drive shaft of the oil pump should be in good condition. When replacing the oil seal in this area, make sure to use a genuine "double-lip" oil seal; do not substitute it with a "single-lip" seal, as single-lip seals are designed only for sealing oil in one direction and do not have the ability to seal air. Our company once experienced a case where, after a major overhaul of a LiuGong ZL50 loader, the hydraulic oil pump exhibited continuous cavitation noise and an automatic rise in the oil tank's oil level. Upon investigation of the hydraulic oil pump repair process, it was discovered that the problem was caused by the incorrect use of a "single-lip" oil seal on the pump's drive shaft. Prevent water from entering the hydraulic system.

　　Excessive moisture in oil can cause corrosion of hydraulic components, emulsification and degradation of the oil, reduced strength of the lubricating oil film, and accelerated mechanical wear. In addition to preventing moisture ingress during maintenance and servicing, it’s also important to ensure that oil storage drums are tightly sealed when not in use—and ideally stored upside down. Oils with high water content should be filtered multiple times, replacing the dried filter paper after each filtration. When no specialized instruments are available for testing, you can test the oil by dropping a small amount onto a heated iron plate: only if no steam is emitted and the oil immediately ignites should it be considered safe to add to the system. During operations, pay special attention to ensuring that mechanical work is carried out smoothly and gently.

　　Mechanical operations should avoid rough handling; otherwise, impact loads will inevitably occur, leading to frequent mechanical failures and significantly shortening the equipment's service life. The impact loads generated during operation not only cause premature wear, fracture, and breakage of mechanical structural components but also create shock pressures within the hydraulic system. These shock pressures, in turn, can damage hydraulic components, prematurely degrade oil seals and the crimped connections between high-pressure hoses and fittings, result in leaks or pipe bursts, and cause frequent activation of relief valves, thereby raising the oil temperature. Another issue worth noting is that operators must maintain steady control. Since each piece of equipment has slightly different free play in its control systems and varying degrees of wear at connection points—resulting in differing clearances—and since the output power of the engine and hydraulic system may also differ, these factors give each piece of equipment its own unique character. Only by carefully observing and adjusting their operating techniques to suit the specific characteristics of the equipment can operators develop good operational habits over time. In the general machinery industry, adhering to a "designated operator for designated machine" system is one of the key factors contributing to this practice.

　　Pay attention to cavitation and overflow noise during operation—always monitor the sounds of the hydraulic pump and the relief valve. If the hydraulic pump emits a “cavitation” noise that cannot be eliminated even after bleeding air, you must identify and rectify the underlying cause before continuing to use it. If a particular actuator moves slowly without any load and is accompanied by the audible sound of the relief valve overflowing, you should immediately stop the machine and perform maintenance.

　　Strictly enforce the shift handover system. When handing over the machinery, the departing driver must ensure that the incoming driver can safely inspect the equipment and accurately check the oil level. Key areas for the incoming driver to inspect include whether the system is leaking, whether connections are loose, whether the piston rod and hydraulic hoses have sustained any damage, whether the low-pressure oil inlet pipe of the hydraulic pump is securely connected, and whether the oil level in the tank is correct. For atmospheric-pressure oil tanks, it’s also essential to inspect and clean the tank’s vent hole, ensuring it remains unobstructed to prevent blockage that could create a vacuum in the tank, making it difficult for the hydraulic oil pump to draw oil and potentially causing damage.

　　Maintaining an appropriate oil temperature is crucial for the hydraulic system's operational efficiency. The ideal operating temperature range for hydraulic systems generally falls between 30°C and 80°C (with a critical temperature exceeding 100°C). If the oil temperature in a hydraulic system becomes too high, it can lead to the following issues: reduced oil viscosity, which increases the likelihood of leaks and decreases system efficiency; weakened lubricating oil film strength, accelerating mechanical wear; formation of carbon deposits and sludge; accelerated oil oxidation, further degrading oil quality; and premature aging of oil seals and high-pressure hoses. To prevent overheating: avoid prolonged overloading; ensure that the radiator fins are not contaminated by oil, as dust accumulation can impair heat dissipation; maintain an adequate oil level to facilitate proper oil circulation and cooling; during hot summer months, avoid continuous operation throughout the day and steer clear of peak midday temperatures. When the oil temperature is too low, the oil becomes highly viscous, flows poorly, encounters greater resistance, and results in lower operational efficiency. If the oil temperature drops below 20°C, sharp turns can easily damage hydraulic motors, valves, and pipelines. In such cases, it’s necessary to perform a warm-up procedure: start the engine and let it idle without load for 3 to 5 minutes. Then, gradually increase the engine speed to a medium level using the throttle, and operate the control lever to move the working device—such as an excavator bucket—to its extreme position, holding it there for another 3 to 5 minutes to allow the hydraulic oil to warm up through overflow. If the oil temperature remains even lower, extend the warm-up period accordingly.

　　In a pressure-type hydraulic tank, it is essential to monitor the tank's air pressure at all times during operation. The air pressure must be kept within the range specified in the accompanying "Operating Manual." If the pressure is too low, the oil pump may fail to draw sufficient oil, potentially leading to damage. Conversely, if the pressure is too high, it can cause leaks in the hydraulic system and increase the risk of rupture in the low-pressure oil lines. For equipment that has undergone maintenance or oil replacement, after completely bleeding the air out of the system, you must check the oil level according to the instructions provided in the accompanying "Operating Manual." Park the machine on a level surface, let the engine idle for 15 minutes, then recheck the oil level. If necessary, add more oil.

　　Other precautions: During operations, take care to prevent flying rocks from striking components such as hydraulic cylinders, piston rods, and hydraulic hoses. If the piston rod sustains minor impact damage, promptly use an oilstone to smooth out the sharp edges around the affected area, thereby preventing damage to the piston rod’s sealing mechanism. As long as there is no oil leakage, the piston rod can continue to be used. For equipment that has been continuously idle for more than 24 hours, before restarting, be sure to add oil into the hydraulic pump to prevent the pump from running dry and getting damaged.