According to some statistics, 70%~85% of the hydraulic system failures are caused by the contamination and deterioration of hydraulic oil. Because all kinds of pump and valve components used in the hydraulic system have high finish mating surfaces and high precision mating gaps between relative moving parts, some components are also equipped with damping holes and slot type control valve ports. If impurities are mixed in the oil, these gaps and holes will be blocked, which will hinder the movement of the oil and damage the normal operation of the hydraulic components. If impurities enter the valve, they may damage the mating surface of the valve core and valve body, or get stuck between them, resulting in poor sealing or ineffective action of the valve. If there is too much dirt in the oil, the oil filter will be blocked and the system circulation will be blocked, the safety valve will often open, the cooling will be poor, and the system temperature will rise. Therefore, keeping the hydraulic system and hydraulic oil clean is the key to maintain the hydraulic system. The main hazards of oil pollution to the system are as follows:

(1) Contamination and wear of components

Various pollutants in the oil cause various forms of wear of components, and solid particles enter the clearance of the moving pair, causing cutting wear or fatigue wear on the surface of parts. The impact of solid particles in high-speed liquid flow on the surface of components causes erosion wear. The water in the oil and the products of oil oxidation deterioration will corrode the components. In addition, the air in the oil of the system causes cavitation, which leads to denudation and damage of the component surface.

(2) Blocking and clamping failure of elements

Solid particles block the clearance and orifice of the hydraulic valve, causing the valve core to be blocked and clamped, affecting the working performance, and even causing serious accidents.

(3) Accelerate deterioration of oil performance

The water and air in the oil are the main conditions for oil oxidation with their heat energy, and the metal particles in the oil play an important catalytic role in the oil oxidation. In addition, the water and suspended bubbles in the oil significantly reduce the strength of the oil film between the motion pairs, reducing the lubrication performance. To this end, the following should be done:

(1) Select appropriate hydraulic oil according to the instructions. ① The type and accuracy requirements of hydraulic oil must be in accordance with the specific provisions and requirements of hydraulic system and component manufacturers; ② If the substitute oil is used for some reason, the performance requirements of the original brand oil shall be met as far as possible; ③ Do not mix hydraulic oils of different brands.

(2) The closed oil tank is adopted, and the air filter with certain accuracy is installed at the inlet of the oil tank.

(3) During use, moisture and emulsion shall be prevented. Dust. Invasion of fiber debris and other mechanical debris.

(4) The amount of hydraulic oil shall be appropriate. The oil volume of the hydraulic oil tank shall be kept within the specified oil level range after the system pipeline and components are filled with oil.

(5) Elements, pipelines and systems must be strictly cleaned before being put into use.

(6) The oil must be filtered strictly. Check the oil filter frequently and replace it if it is dirty.

(7) Regularly check the quality of hydraulic oil and keep it clean. When checking the quality of hydraulic oil, the following three aspects are mainly checked: ① The oxidation degree of hydraulic oil. During the use of hydraulic oil, due to the change of temperature, the effect of oxygen in the air and sunlight, it will be gradually oxidized, which will change its viscosity and other properties. The degree of oxidation is usually judged from the color and smell of hydraulic oil. If the hydraulic oil is dark brown and has a foul smell, it indicates that it has been oxidized. The darker the brown color is, the stronger the odor is, which indicates that the oxidation is more severe. At this time, replace the oil. ② The degree of water content in the hydraulic oil If water is mixed in the hydraulic oil, its lubricating performance will be reduced and the metal will be corroded. There are usually two methods to judge the degree of water mixed in hydraulic oil. One is based on the change of its color and smell. If the color of hydraulic oil is milky white and the smell does not change, it means that there is too much water mixed. Second, take a small amount of hydraulic oil and drop it on the hot iron plate. If it makes a "bell" sound, it means it contains water. At this time, replace the oil. ③ If the hydraulic oil contains impurities, after the machine has been working for a period of time, take a few drops of hydraulic oil and put them on your hand. Twist them with your fingers to see if there are metal particles, or observe if there are tiny flash points in the sun. If there are more metal particles or flash points, it is proved that the hydraulic oil contains more mechanical impurities. At this time, the hydraulic oil shall be replaced, or the hydraulic oil shall be drained for sedimentation for not less than 42h, and then filtered for use.

(8) When replacing the hydraulic oil, pay attention to that it should be discharged when the hydraulic oil is hot just after the machine has finished working (so as to easily bring out mechanical impurities, oil stains, etc.). The specific method is: control the working device to place it at the highest position, shut down the engine, use its dead weight to lower, make the oil cylinder completely drain, then thoroughly clean the oil tank and corresponding pipelines, and add new hydraulic oil.

(9) Clean the hydraulic system correctly. It is better to use hydraulic oil with the same brand that has been used in the system. Never use kerosene or diesel as cleaning fluid. During cleaning, the flow shall be as large as possible to make the liquid flow in the pipeline turbulent, and complete the action of each actuating element, so as to flush out pollutants from each pump, alarm cylinder and other elements. After cleaning, drain the cleaning fluid in hot state and add new working fluid according to the method of oil replacement.

Prevent excessive oil temperature

According to the experiment, the temperature of the hydraulic system is generally the most appropriate within the range of 35t~60 ℃, and the maximum temperature should not exceed 80 ℃. Under normal oil temperature, various performances of hydraulic oil are good. Too high oil temperature will cause many adverse effects on the hydraulic system, such as viscosity reduction, thin and easily damaged lubricating oil film, poor lubricating performance, low volumetric efficiency, increased mechanical wear, accelerated aging of rubber seal rings, and reduced sealing performance. Therefore, the oil temperature of the system shall be controlled to keep within the normal range during use.

To this end, the following should be done:

(1) Maintain the normal oil volume in the oil tank, so that the system has enough oil for circulating cooling.

(2) When the actuator does not work, the system shall be unloaded in time.

(3) Clean the cooling device frequently to keep it in good working condition.

(4) The hydraulic oil with proper viscosity shall be selected according to the working environment temperature: high viscosity oil shall be selected in case of high ambient temperature, and low viscosity oil shall be selected in case of low ambient temperature. Under general ambient temperature, 18~38pf/s oil at 50 ℃ should be selected for gear pump.

(5) When the temperature is high, the machinery cannot operate continuously for a long time. Generally, when the temperature is higher than 30 ℃, the continuous operation time of the machinery shall not exceed 4h.

(6) When the air temperature is lower than 10 ℃, the system shall be operated under no-load condition for about 20min to raise the oil temperature to the specified value.

Prevent air from entering the hydraulic system

After the hydraulic system is filled with air, the hydraulic oil will be "emulsified" and the performance of the oil will be damaged. The volume of air entering the oil changes with the change of system pressure and temperature, hindering the movement of fluid flow, thus causing the hydraulic actuator to stop and move, slow speed, insufficient force and other phenomena during operation, which is usually called "work creep". The creeping phenomenon not only destroys the stability of the hydraulic system, but also sometimes causes vibration and noise.

Therefore, air must be strictly prevented from entering the hydraulic system. The specific methods are as follows:

(l) Pay attention not to air leakage at the sealing part of oil suction pipeline and drive shaft end of the pump that is lower than atmospheric pressure.

(2) Prevent air from being carried by the oil return pipe orifice, and do not expose the oil return pipe to the surface of the oil tank.

(3) If air has been introduced into the system, the leaking part shall be found out in time for elimination. And remove the air entering the system.

(4) After adding new oil, the working device shall be continuously operated to lift, lower and turn over so as to remove air from the system. Correctly implement the operating procedures and prevent rough and random operation.

During excavation, rotation, shoveling, lifting and other operations, the action must be stable and accurate. The operating lever must be retracted and released in a timely manner to avoid being too violent or too fast, so as to avoid pressure impact when suddenly opening or closing the oil inlet and outlet of the hydraulic cylinder, hydraulic motor and other actuators, which may lead to accelerated damage of oil seals, blistering and cracking of high-pressure hoses, and loosening and leakage of pipe joints, It may even cause the overflow valve to jam the valve core due to excessive instantaneous opening, causing internal leakage, resulting in weak operation, reduced work efficiency and shortened service life. Strengthen the daily maintenance of the hydraulic system.