Leakage, Causes and Prevention of Hydraulic System of Construction Machinery
Leakage is a common fault phenomenon in hydraulic machinery, especially in the hydraulic system of construction machinery, mainly due to the pressure difference caused by the liquid flowing in the hydraulic components and pipelines and the leakage of the components. In addition, poor working conditions will also have a certain impact on the sealing of construction machinery. Once a hydraulic system leaks, it will cause the system pressure to fail to build up, hydraulic oil leakage will also cause environmental pollution, affect production and even produce serious consequences that cannot be estimated.
There are mainly two types of leakage in the hydraulic system of construction machinery: leaks at fixed seals and leaks at moving seals. The leaks at fixed seals mainly include the bottoms of cylinders and the joints of various pipe joints. The motion seals mainly include the cylinder piston rods. Multiple valve stems and other parts. Leakage from oil can also be classified into external leakage and internal leakage. External leakage mainly refers to the leakage of hydraulic oil from the system to the environment. Internal leakage refers to the existence of pressure difference between the high and low pressure side and the failure of seals. The hydraulic oil flows from the high pressure side to the low pressure side within the system.
Three major causes of leaks
1, design factors
1 Selection of seals
The reliability of the hydraulic system depends to a large extent on the design of the hydraulic system seal and the choice of seals. Due to the unreasonable use of the seal structure in the design, the selection of seals does not conform to the specification, and the hydraulic oil is not taken into account in the design. Sealing material type of compatibility, load conditions, limit pressure, working speed, environmental temperature changes. All of these causes the hydraulic system leakage directly or indirectly to varying degrees. In addition, due to dust and impurities in the operating environment of the construction machinery, appropriate dust seals should be selected in the design to prevent dust and other dirt from entering the system to destroy the seal and contaminate the oil, thereby causing leakage.
2 other design reasons
The design takes into account that the geometric accuracy and roughness of the moving surface are not comprehensive enough, and the strength check of the joints is not performed in the design, etc., and these all cause leakage in the mechanical work.
2, manufacturing and assembly factors
1 manufacturing factors
All hydraulic components and sealing components have strict dimensional tolerances, surface finishes, surface finishes, and geometric tolerances. If in the manufacturing process, such as: the piston radius of the cylinder, the depth or width of the sealing groove, the hole size of the sealing ring is too bad or out of round due to processing problems, there are burrs or defects, chrome plating off, etc. The parts will be deformed, scratched, crushed, or inaccurate, causing them to lose their sealing function. This will cause the part itself to have congenital leaks and leaks after assembly or during use.
2 assembly factors
In the assembly of hydraulic components should be barred from the operation, if excessive force will cause the parts to be deformed, especially with copper rods, such as tapping the cylinder body, sealing flanges, etc.; should be carefully checked before assembly, assembly parts should be a little hydraulic Oil, press gently, use diesel oil during cleaning, especially rubber elements such as seals, dust rings, o-rings, etc. If you use gasoline, it will easily lose its original elasticity and lose its sealing function.
3, oil pollution and parts damage
1 Gas pollution
At atmospheric pressure, about 10% of the air can be dissolved in the hydraulic fluid. Under the high pressure of the hydraulic system, more air or gas will be dissolved in the fluid. Air forms bubbles in the oil. If the hydraulic support is in operation for a very short period of time, the rapid pressure change between high and low pressure will cause the bubbles to generate high temperatures on the high pressure side and burst on the low pressure side if the components of the hydraulic system When there are pits and damage on the surface, the hydraulic oil will rush toward the surface of the component to accelerate the wear of the surface and cause leakage.
2 particle pollution
Hydraulic cylinders are the main actuators of some hydraulic systems of construction machinery. Since the piston rods are exposed directly to the environment during the working process, they are in contact with the environment. Although the guide sleeves are equipped with dust-proof rings and seals, they are also difficult to prevent dust and dirt. Into the hydraulic system to accelerate the scratches and wear of the seals and piston rods, causing leakage, particle contamination is one of the fastest factors of hydraulic components.
3 Water pollution
Due to the influence of factors such as wet work environment, the water may enter the hydraulic system. The water reacts with the hydraulic oil to form acidic substances and sludge, which reduces the lubrication performance of the hydraulic oil and accelerates the wear of the components. The water also causes the valve of the control valve. Sticking occurs in the rod, making it difficult to control the valve to scratch the seal and cause leakage.
4 parts damage
The seals are made of materials such as oil-resistant rubber, which can cause system leaks due to aging, cracking, and damage due to prolonged use. If a part is damaged by a collision during operation, it can scratch the sealing element and cause a leak.
Main leakage prevention measures
The factors causing the leakage of the hydraulic system of the construction machinery are the result of comprehensive influence in many aspects. It is very difficult to fundamentally eliminate the leakage of the hydraulic system with the existing technology and materials. Only from the above factors that affect the hydraulic system leakage, take reasonable measures to minimize leakage of the hydraulic system. The design and processing of sealed grooves must be fully considered in design and processing. In addition, the choice of seals is also very important, if not fully consider the impact of the initial leakage factors, will bring incalculable losses in the future production. Choose the right assembly and repair method and learn from past experience. For example, special tools are used in the assembly of the seal ring, and some grease is applied to the seal ring. In the control of hydraulic oil pollution, we must start with the source of pollution, strengthen the control of pollution sources, and take effective filtration measures and regular oil quality inspections. To effectively cut off the external factors (water, dust, particles, etc.) on the hydraulic cylinder pollution, you can add some protective measures.