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Hydraulic System Failures and Solutions

2021-08-31
Hydraulic system failures and solutions
Most of the failures of the hydraulic system do not happen suddenly. Generally, there are always signs, such as noise, vibration, impact, crawling, pollution, cavitation, and leakage. If these phenomena can be discovered in time, and properly controlled and eliminated, system failures can be eliminated or relatively reduced.Hydraulic system leakage: The hydraulic system leakage is divided into internal leakage and external leakage. System leakage will affect the performance of hydraulic components, increase energy consumption, and pollute the environment. The causes and troubleshooting methods of system leakage are as follows.

(1) The system pressure is adjusted too high. Under the same conditions, the higher the pressure of the system, the greater the possibility of leakage. Therefore, the pressure of the system should be adjusted to the best value according to the requirements.

(2) There are too many oil pipe joints, the screws of the pipe joints are loose, and the screws on the joint surface or each sealing surface are loose. Reduce tubing joints and elbows, and tighten loose screws.

(3) Improper selection of seals, damage, aging and improper assembly will cause leakage. Choose each sealing device reasonably, and replace the aging and damaged seals with new ones in time. If there are assembly deviations, they should be re-adjusted and assembled.

(4) Too high oil temperature not only reduces the viscosity of the oil and increases leakage, but also accelerates the aging of the seals, causing serious system leakage. Strictly control the temperature of the hydraulic system. In order to improve the heat dissipation of the system, a cooler can be added or the heat dissipation performance of the fuel tank can be improved.

2. Creeping phenomenon

(1) Creep caused by poor rigidity of the drive member

Under normal conditions, after the air enters the oil, most of it is dissolved in the pressure oil, and the remaining small part forms bubbles and floats in the pressure oil. In the low pressure state, the air dissolved in the oil escapes, generating bubbles and forming cavitation. In addition, the compressibility of the air causes the hydraulic oil to produce obvious elasticity, resulting in poor rigidity of the driving member and causing crawling.

(2) Creeping caused by large gaps in hydraulic components

①Crawling caused by low-speed movement of moving parts. When the moving parts move at low speed, once dry friction occurs, the resistance increases. At this time, the hydraulic pump is required to increase the pressure, but due to the large gap of the hydraulic pump, the oil leaks seriously and cannot adapt to the crawling caused by the pressure change of the actuator due to the change of resistance. At this time, the internal parts of the hydraulic pump should be repaired or replaced to ensure the clearance required by the assembly to reduce the leakage of the hydraulic pump.

②Crawling caused by control valve failure. The damping holes and throttles of various control valves are blocked by dirt, the valve core is not flexible, etc., so that the pressure fluctuates greatly, causing the thrust or flow to be large and sometimes small and creeping. Therefore, it is necessary to keep the oil clean, clean and replace it regularly, and strengthen the maintenance of the components to prevent the hydraulic oil from being polluted.

③Crawling caused by component wear. Due to the wear of valve parts, the matching clearance increases, and part of the high-pressure oil and the low-pressure oil communicate with each other, causing insufficient pressure. In addition, the clearance between the piston of the hydraulic cylinder and the inner hole of the cylinder increases due to wear, and internal leakage occurs, which reduces the pressure difference between the two chambers of the hydraulic cylinder, resulting in a reduction in thrust, resulting in creeping due to changes in friction at low speeds. The specific measures are to carefully inspect the fit clearance, research and match or redo components, ensure the fit clearance, and replace the damaged seals.

(3) Creeping caused by changes in frictional resistance

This phenomenon mostly occurs in hydraulic cylinders. The main reason is that the center line of the hydraulic cylinder is not parallel to the piston rod, the piston rod is bent partially or over the entire length, the inner circle of the cylinder is roughened or scratched, and the piston and the piston rod are not on the same axis. The accuracy of the cylinder barrel does not meet the technical requirements, and the oil seals at both ends of the piston rod are adjusted too tightly and other factors will cause crawling. The elimination measures taken are to inspect the accuracy and damage of the hydraulic cylinders item by item, and repair or update them. The installation accuracy of the hydraulic cylinder should meet the technical requirements.

3. Hydraulic clamping

Hydraulic clamping means that the pressure oil in the hydraulic system flows through the cylindrical slide valve structure of ordinary hydraulic valves, and the radial imbalance force acting on the spool causes the spool to jam. Hydraulic clamping is easy to accelerate the wear of the slide valve, reduce the service life of the components, affect the action of the control components, and cause the system to produce undesirable consequences. The radial unbalance force caused by the geometric error of the sliding valve movement pair and the change of coaxiality is the main reason for the hydraulic clamping. In view of this situation, a uniform groove can be provided on the surface of the valve core to improve the manufacturing accuracy of the valve core and the valve hole, and to ensure the matching clearance. At the same time, the cleanliness of hydraulic oil is improved to prevent particles from invading the slide valve. In addition, the adsorption of polar molecules in the hydraulic oil and the embedding of impurities in the hydraulic oil into the gap can also cause hydraulic clamping.

Hydraulic system

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