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1. "Pathogenic" factors of hydraulic system

In the hydraulic transmission system, there are some more precise parts. People feel that the hydraulic transmission of machinery is labor-saving and convenient, but at the same time, it is easy to be damaged. The main reason is that we don't know its working principle and structural characteristics, so we don't know its preventive maintenance methods.

There are three basic "pathogenic" factors in the hydraulic system: pollution, overheating and air entry. These three unfavorable factors are closely interrelated. The emergence of any one of them will lead to another or more problems. Practice has proved that 75% of the causes of "disease" in the hydraulic system are caused by these three factors.

If there is no problem with the manufacturing quality of the hydraulic system, most of the causes of the failure are improper prevention and maintenance, and there are generally few factors of improper operation. This is mainly due to the lack of understanding of its working conditions. If we understand some basic principles and understand the above three harmful factors leading to the failure, we can ensure that the system is in good working condition for a long time.

2. Common faults of hydraulic system

2.1 working oil deteriorates due to dirt

The sources of dirt (such as ash, sand, soil, etc.) entering the oil include:

(1) The outside of the hydraulic system is not clean. Unclean objects are brought into the system when refueling or checking the oil quantity, or enter the system through damaged oil seal or sealing ring;

(2) Internal cleaning is not complete. There is still a trace of dirt residue in the oil tank or components;

(3) Dirty refueling containers or appliances;

(4) Rust scale is generated in the pipe due to hot bending of oil pipe during manufacturing;

(5) Improper oil storage, dirty or deteriorated before being added to the system;

(6) Oil that has gradually deteriorated will corrode parts. The corroded metal may become free molecules suspended in the oil.

Dirt will cause wear and corrosion of parts, especially for finished parts, which will scratch the inner wall of rubber hose, oil seal ring and packing. After these things are damaged, more dirt will enter the system, forming a vicious circle of damage.

2.2 overheating

Overheating of the system may be caused by one or more of the following reasons:

(1) Air or moisture enters the oil. When the hydraulic pump changes the oil into pressure oil, the air and moisture will contribute to the increase of heat and cause overheating;

(2) The oil level in the container is too high and the oil is strongly stirred, resulting in overheating;

(3) Poor quality oil may become thin, causing foreign substances to suspend, or have affinity with water, which will also cause heat generation;

(4) When working, it exceeds the rated working capacity, resulting in heat;

(5) Improper adjustment of the return valve or failure to replace damaged parts in time will sometimes produce heat.

Overheating will make the oil oxidize rapidly, and the oxidation will release insoluble resin, sludge and acids. These substances accumulate in the oil, resulting in accelerated wear and corrosion of parts, and they adhere to the surface of finished parts, which will also make the parts lose their original functions. The thinning of oil due to overheating will also slow the transmission.

The result of the above overheating is often reflected in the slow transmission action and the stuck oil return valve during operation.

2.3 incoming air

There are several reasons for air entering the oil:

(1) Improper pouring down during refueling, resulting in bubbles mixed into the oil and brought into the pipeline;

(2) The joint is loose or the oil seal is damaged, and the air is sucked in;

(3) The oil suction line is worn through, scratched or corroded, so air enters.

In addition to overheating caused by air entering the oil, a considerable amount of air will be dissolved in the oil under pressure. If the compressed volume is about 10% of the dissolved air, it will form foam when the pressure drops. When the working hydraulic cylinder is decompressed, the foam oil will form the sponge character. In addition, many bubbles in the oil will increase the total volume, causing oil spills or oil spills.

The working oil containing air will produce jerk spasm when transmitting power, resulting in uneven power transmission. The resulting pressure fluctuation and stress will damage the parts and, in serious cases, the whole system.

The working oil containing air will also cause the risk of cavitation of the hydraulic pump, resulting in greater suction, which will suck more air and other impurities into the system. Overheating is caused by air entering the oil, and dust will be brought into the air at the same time. These conditions will make the oil deteriorate quickly.

3. How to maintain the hydraulic system

It can be seen from the above that pollution, overheating and entering the air are intrinsically related. Therefore, comprehensive prevention should be carried out to ensure the normal operation of the hydraulic system. Therefore, it is necessary to establish a special preventive maintenance system for the hydraulic system, and its primary task is to strictly check the condition of working oil. During oil change, maintenance service personnel shall participate in and help conduct a comprehensive inspection of the system. The inspection items include:

(1) Check whether all pipeline systems are flattened, bent and damaged, and whether hoses are kinked, scratched or excessively bent;

(2) In order to prevent any tiny dust and dirt from sticking to internal parts, the whole system shall be cleaned with steam when possible;

(3) check the oil tank or oil conservator, check whether the oil level is enough, and pay attention to whether the process of oil filling causes bubbles, surges or eddy currents. These phenomena are entering air symptoms, and bubbles appear in the vent ports, which prove that they have entered the air.

(4) Check whether the pipeline and other components are stripped due to overheating, whether there is burning smell, and whether the oil turns black and thick. Measure the oil temperature with a thermometer;

(5) Apply soap foam to the joint to check for leakage. Where there is leakage, there may be oil, because the oil will absorb dirt, but where there is oil, there may not be leakage. In addition, overheating often implies leakage, and the joints found to have leakage should be tightened at any time;

(6) Listen for any abnormal sound. The "click" sound of the hydraulic pump indicates that it may be cavitation caused by entering the air, or it has been worn by dirt;

(7) Check the working capacity of the hydraulic pump regularly.

4. How to troubleshoot

The inspection of the above items shall be recorded every time and accumulated into files, so as to help prevent or eliminate the problems that are easy to occur in the future. As for the faults that have occurred, the following steps can be taken to eliminate them:

(1) Drain the old oil;

(2) Clean or replace the filter core and oil filter screen;

(3) Clean the oil reservoir and vent. When scrubbing, use cloth instead of cotton yarn;

(4) Disassemble all main assemblies and clean all parts with diesel (do not use gasoline, because the surface of precision parts washed with gasoline will be dry).