According to statistics, hydraulic system failures rank first in the proportion of failures in various systems of loaders. What factors cause hydraulic system leakage? How to solve it?

Classification of hydraulic system leaks

The leakage of the hydraulic system of the loader is mainly caused by the pressure difference generated when the liquid flows in the hydraulic components and pipelines and the gaps between the components.

There are two main types of oil drain in the hydraulic system of the loader, one is the oil drain sealed by the static joint surface (that is, the fixed part, mainly including the joint between the cylinder head and the cylinder barrel, the connection of each pipe joint, etc.); The joint surface (that is, the sliding part, mainly including the valve stem of the multi-way valve, the cylinder piston and the inner wall of the cylinder barrel, the piston rod and the cylinder head guide sleeve, etc.) is sealed to drain the oil.

It is specifically manifested as external leakage and internal leakage. External leakage mainly occurs outside the hydraulic system, that is, oil leaks from each component of the hydraulic system to the external environment. Internal leakage refers to the flow of hydraulic oil from the high pressure side to the low pressure side inside the system due to the existence of the pressure difference between the high and low pressure sides and the failure of the seal.

factors causing leakage

1. Selection of hydraulic oil

Hydraulic oil is not only a medium for power transmission in the hydraulic system, but also a lubricant and coolant. To ensure that the hydraulic system can work reliably, effectively and economically under various conditions, the hydraulic oil must have suitable viscosity and good viscosity-temperature characteristics. Viscosity is an important indicator of hydraulic oil. For a certain hydraulic system, only the working medium with a limited range of viscosity can be used to work normally. If the viscosity is too high, the resistance will increase when the oil flows, the temperature rises quickly, the energy loss will be large, and the system efficiency will be reduced; Leakage increases.

2. Oil pollution

1) Gas pollution

Under atmospheric pressure, about 10% of the air can be dissolved in the hydraulic oil, and under the high pressure of the hydraulic system, more air or gas will be dissolved in the oil. Air forms air bubbles in the oil. If the hydraulic system is working, the pressure changes rapidly between high and low pressure in a very short period of time, which will cause the air bubbles to generate high temperature on the high pressure side and burst on the low pressure side. If the hydraulic system is When there are pits and damage on the surface of the component, the hydraulic oil will rush to the surface of the component at high speed to accelerate the wear of the surface and cause leakage.

2) Water pollution

Due to the influence of humidity in the working environment and other factors, external water may enter the hydraulic system, and the water will react with the hydraulic oil to form acidic substances and sludge, which will reduce the lubricating performance of the hydraulic oil and accelerate the wear of components. Corrosion of the valve stem makes it difficult to operate the control valve and scratches the seals, causing leakage.

3) Solid particle pollution

The hydraulic cylinder is the main actuator of the hydraulic system of the loader. Since the piston rod is exposed and directly in contact with the environment during the working process, although the guide sleeve is equipped with dust-proof rings and seals, it is inevitable that dirt will be brought into the hydraulic system. , Accelerate the scratches and wear of seals and piston rods, etc., causing leakage.

3. The reason for the parts

1) The joint surface of hydraulic components is damaged during assembly and maintenance, or the paper pad is damaged by pressure oil, or there is a flatness error on the joint surface during the repair process, or the joint screw is not tightened, etc., which may cause joint surface leakage; if brutal operation, Excessive force, especially hitting the cylinder body and sealing flange with copper rods, etc. will deform the parts and cause leakage.

2) The seal is made of oil-resistant rubber and other materials. Due to long-term use, aging, cracking, damage, etc. will cause system leakage. If the part is damaged by collision during operation, it will scratch the sealing element and cause leakage. Or the system pressure is too high, causing the seal to fail and cause leakage.

3) Increased spool clearance in the hydraulic control valve leads to increased leakage.

Measures to prevent hydraulic system leakage

In order to prevent and control the leakage of the loader's hydraulic system, strengthening the management of hydraulic oil and standardizing maintenance and repair procedures are important ways to control hydraulic oil pollution and ultimately prevent hydraulic system leakage. Therefore, the following three aspects of management must be strengthened in actual engineering construction:

1. Reasonable selection of hydraulic oil, standardization of hydraulic oil storage and transportation management

1) There must be a reasonable management organization and strict rules and regulations, and strengthen the selection and management of hydraulic oil and hydraulic components.

2) Newly purchased hydraulic oil should be sampled and inspected. Only after passing the test can it be put into storage. The hydraulic oil in stock should be inspected regularly. If it does not meet the performance indicators, it is not allowed to be used.

3) Hydraulic oils of different grades should be stored in different categories, and mixed loading and storage are strictly prohibited to prevent mixed use.

4) Carry out regular quality inspections, and the hydraulic oil that meets the specified requirements can be shipped out of the warehouse.

5) The hydraulic oil should be filtered before use to ensure that the impurity content of the hydraulic oil meets the specified requirements.

2. Strictly abide by the warranty regulations to ensure the quality of the warranty

First of all, the hydraulic system of the loader must be maintained in strict accordance with the maintenance procedures of the hydraulic system of the loader on a regular basis.

Secondly, in the process of maintenance, repair and assembly of the hydraulic components of the loader, strictly follow the specified requirements to prevent the hydraulic oil from being polluted and prevent the mixing of dust, water and air.

At the same time, strictly control the machining accuracy, surface roughness and reduce the fit gap and assembly error to prevent the surface damage of the components due to improper operation and cause leakage.

3. Clarify job responsibilities and strengthen protection during use

1) The loader randomly establishes a registration card, records the name and grade of the hydraulic oil to be used, and indicates the date and quantity of each refueling or oil change, so as to avoid mixing hydraulic oil during work.

2) According to the instruction manual, clean or replace the hydraulic oil filter element regularly in combination with the actual use conditions, and check the hydraulic oil level every day, and replenish it in time if it is insufficient. At the same time, remove the air in the hydraulic system according to the mechanical operation manual to prevent leakage caused by hydraulic oil pollution.

3) Analyze the oil samples of the hydraulic oil regularly according to the conditions of use. If serious oil pollution is found, the cause should be found out immediately and eliminated in time.

4) Control the working temperature of the hydraulic oil (the maximum temperature of the system does not exceed 80°C, and the temperature in the hydraulic oil tank does not exceed 60°C). The increase in oil temperature will accelerate the oxidation and deterioration of the hydraulic oil, the life of the oil will be greatly shortened, and the oil will be oxidized and deteriorated. The acidic substances in the pump have a corrosive effect on the pump, motor, etc., the seals are aging and deformed, and the mating surface is thermally deformed, which increases wear and tear, resulting in increased leakage.

5) When troubleshooting the hydraulic system, you should follow the rules, keep it clean, prohibit random dismantling, and prevent pollutants from entering the hydraulic system. Cleaning and performance tests must be carried out after assembly. On the one hand, the repair quality can be tested, and on the other hand, impurities can also be cleaned. All hydraulic pipes should be protected and sealed.

6) Regularly check the pressure, flow and temperature of each testing point of the hydraulic system to prevent the hydraulic system from working under abnormal pressure and temperature for a long time, which can reduce the wear and tear of the hydraulic system, prevent internal leakage, and ensure the normal operation of the hydraulic system.

The leakage problem of the hydraulic system of the loader is the result of the comprehensive influence of many aspects. It is not possible to simply, traditionally and negatively strengthen the seal, but to systematically eliminate the root cause of the leakage and take effective measures to control it.

Starting from the factors that affect the leakage of the hydraulic system, take reasonable measures to minimize the leakage of the hydraulic system. Especially in the process of use, the management, operation and maintenance personnel of the loader should strengthen their sense of responsibility, based on prevention, and minimize the leakage of the hydraulic system of the loader.