Hydraulic oil serves as the working medium in hydraulic transmission systems, playing a crucial role in transmitting, converting, and controlling energy. At the same time, it provides lubrication, corrosion prevention, rust inhibition, and cooling for various components within the hydraulic system. Controlling contamination in hydraulic systems of construction machinery ensures their proper operation, thereby extending the machinery's service life and enhancing its value.

Hydraulic Oil Contamination Control Measures

Select the correct hydraulic oil.

a. You should choose high-quality, wear-resistant hydraulic oil and, whenever possible, opt for hydraulic oil that matches the brand and grade specified by the original equipment manufacturer. Currently, there are numerous manufacturers and suppliers of hydraulic oil both domestically and internationally, and hydraulic oils vary significantly in quality—some are superior, while others are inferior or even counterfeit. Therefore, you should purchase hydraulic oil only from suppliers designated by the manufacturer or from specialized stores run by major manufacturers. It is advisable to raise the requirements for solid particle contamination levels to control hydraulic oil contamination at its source. Newly purchased hydraulic oil must undergo sampling inspection; only after passing the inspection can it be filtered using a high-precision oil filter before being poured into the hydraulic oil tank. During machine operation, hydraulic oil samples should be regularly taken for analysis to assess contamination levels, and any hydraulic oil that fails to meet the required standards should be replaced promptly. Before replacement, the hydraulic system must be thoroughly cleaned. The equipment management department must shift away from its previous management approach, which focused solely on procurement without paying attention to quality conditions, and strictly enforce quality controls at the point of hydraulic oil import.

b. Hydraulic oils of different grades and specifications must not be mixed. Hydraulic oils of different grades have varying physicochemical properties; mixing them may trigger chemical reactions, corrode hydraulic components, and damage the hydraulic system.

c. If another hydraulic oil is to be used in place of the original hydraulic oil, the substitute hydraulic oil must be tested by an authoritative agency, and its key technical specifications must be identical to or closely similar to those of the original hydraulic oil. Moreover, the substitute hydraulic oil must not be mixed with the original hydraulic oil.

Control the machining, assembly, and transportation processes of hydraulic components.

When signing the purchase contract for hydraulic components, clear requirements must be specified regarding aspects such as solid particle contamination levels. During transportation and storage, all oil ports must be fitted with sealing caps, and hydraulic components must be properly packaged. Before and after unpacking, careful inspections should be conducted to prevent contamination, and remedial measures should be taken whenever necessary. For hydraulically-related parts machined in-house, each step of the manufacturing process must undergo thorough cleaning and purification, and prior to assembly, these parts must also be meticulously cleaned again.

Strictly control the purification of hydraulic oil.

a. Regenerated contamination refers to the contamination generated during the operation of a hydraulic system. It mainly includes wear particles from moving parts, rust on components, flaking paint, and degradation of the hydraulic oil itself. To effectively prevent regenerated contamination, filters should be installed at appropriate locations within the hydraulic system, and filter elements should be regularly inspected, cleaned, or replaced. During operation, it is important to monitor and control the temperature of the hydraulic oil carefully, avoiding excessively high oil temperatures that could accelerate oxidation and degradation, thereby generating various contaminants.

b. Before hydraulic oil is put into storage, it must be sampled and tested; only oil that passes the test may be admitted to the warehouse. Stored hydraulic oil should be sampled and tested regularly, and any oil that fails the test must not be used. Oil received into the warehouse should be stored and managed according to its grade and serial number, and mixing different grades is strictly prohibited. Oil products must not be stored in the open air. If outdoor storage is unavoidable, extra measures must be taken to protect against rain, or oil drums should be stored at an angle to prevent rainwater from seeping in through the drum openings and contaminating the hydraulic oil.

c. When replacing the oil, thoroughly drain any residual fluid from the oil tank, remove any sediment, and carefully rinse the inside of the tank with an appropriate amount of the new oil to be added. Old oil remaining inside components can be drained using a jog-start method. It is essential to establish, through institutional measures, a regular schedule for cleaning or replacing filters, thereby enhancing the hydraulic system’s “immunity.” Replace or clean the filter elements regularly—or as indicated by the indicator—ensuring filtration accuracy and preventing secondary contamination of the hydraulic oil.

Control the operation process

a. Mechanical actions should be gentle and smooth, avoiding impact loads that could cause excessive resistance, premature wear, or even fracture of the machinery. Meanwhile, impact pressures generated by hydraulic systems often lead to damage or leakage in components, oil seals, and high-pressure hose fittings.

b. If the hydraulic pump, hydraulic motor, relief valve, or other components emit unusual noises during operation, or if the working assembly moves slowly without any load and is accompanied by the sound of the relief valve, the machine should be stopped immediately and the cause carefully investigated.

c. If leakage occurs in the seal during operation, it should be addressed promptly to prevent contaminants from entering the hydraulic system.

d. Prevent the hydraulic oil temperature from becoming too high during operation. High oil temperatures can easily lead to leaks, accelerate oil oxidation, and cause accelerated wear of hydraulic components as well as premature aging of oil seals and hoses.

Control the maintenance and upkeep process

a. When assembling and sealing components in service, work as much as possible on a clean indoor workbench. Maintenance personnel should wear neat attire to prevent fibers, dust, and other contaminants from entering the hydraulic system.

b. As a general rule, the cleaning fluid should be kerosene or hydraulic oil of the same grade; diesel can also be used. After cleaning, the components should be placed in a clean container.

c. Some hydraulic components, such as hydraulic pumps and hydraulic motors, must be filled with oil after assembly; otherwise, they will suffer premature wear.

d. Before refueling, you must check the cleanliness of the hydraulic oil tank and clean it if necessary.

Among the failures that occur in hydraulic systems—such as common issues like system blockages, valve sticking, control malfunctions, seal damage, cavitation, and corrosion—80% to 90% are caused by hydraulic oil contamination. The primary sources of hydraulic oil contamination are impurities and moisture. As long as impurities are effectively controlled and the oil quality is consistently maintained at or below NAS8 level, the service life of equipment can be extended by a factor of two to three.

Establish corresponding rules and regulations.

All measures to control hydraulic oil contamination must be institutionalized and implemented at every work procedure, on every machine, at every testing device, and at every job position.

In summary, the working medium of a hydraulic system is hydraulic oil, often referred to as the “blood” of the hydraulic system. The quality of this hydraulic oil directly affects the normal operation of the entire system. By maintaining high cleanliness of the hydraulic oil within the hydraulic system over the long term, we can naturally reduce various adverse effects caused by oil contamination, achieving preventive benefits, extending the service life of hydraulic machinery and components, and lowering the rate of mechanical failures. This, in turn, helps to conserve energy and reduce costs. Only on this solid foundation can the hydraulic system operate more stably and have a longer service life.