Leakage is a common fault phenomenon in hydraulic machinery, especially in the hydraulic system of construction machinery. It is mainly caused by the pressure difference when the liquid flows in the hydraulic components and pipelines and the gaps in the components. In addition, harsh working conditions will also have a certain impact on the sealing of construction machinery. Once the hydraulic system leaks, the system pressure will not be able to build up, and the hydraulic oil leakage will also cause environmental pollution, affect production and even produce unpredictable serious consequences.
Classification of leaks
There are two main types of leakage in the hydraulic system of construction machinery. The leakage at the fixed seal and the leakage at the moving seal. The leakage at the fixed seal mainly includes the bottom of the cylinder and the connection of each pipe joint. The moving seal mainly includes the piston rod of the cylinder, Multi-way valve stem and other parts. The oil leakage can also be divided 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 sides and the failure of the seal. Make the hydraulic oil flow from the high pressure side to the low pressure side inside the system.
Three reasons affecting leakage
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 selection of the seals. Due to the unreasonable selection of the seal structure in the design, the selection of the seals does not conform to the specifications, and the hydraulic oil and the The compatible type of sealing material, load condition, ultimate pressure, working speed, environmental temperature change, etc. These all directly or indirectly cause hydraulic system leakage to varying degrees. In addition, due to dust and impurities in the operating environment of construction machinery, suitable dust-proof seals should be selected in the design to prevent dust and other dirt from entering the system to damage the seal and contaminate the oil, resulting in leakage.
②Other design reasons
The design takes into account that the geometric accuracy and roughness of the moving surface is not comprehensive enough, and the strength of the connection part is not checked in the design, which will cause leakage in the work of the machine.
2. Manufacturing and assembly factors
① Manufacturing factors
All hydraulic components and sealing parts have strict dimensional tolerances, surface treatment, surface finish and shape tolerances. If it is out of tolerance in the manufacturing process, such as: the piston radius of the cylinder, the depth or width of the seal groove, the size of the hole with the seal ring is out of tolerance or due to processing problems, it has burrs or depressions, and the chrome plating falls off. The parts will lose the sealing function due to deformation, scratches, crushing or uncompacting. It will cause the part itself to have a congenital leakage point, which will cause leakage after assembly or during use.
②Assembly factors
The hydraulic components should be free from brutal operation during assembly. Excessive force will cause the parts to deform, especially the cylinder block, sealing flange, etc. with copper rods, etc.; the parts should be carefully checked before assembly, and the parts should be dipped in a little hydraulic pressure during assembly. Oil, lightly press in, use diesel when cleaning, especially rubber components such as seals, dust rings, o-rings, etc. If gasoline is used, it will easily age and lose its original elasticity, thereby losing its sealing function.
3. Oil pollution and damage to parts
①Gas pollution
Under atmospheric pressure, about 10% of the air can be dissolved in the hydraulic oil. Under the high pressure of the hydraulic system, more air or gas will be dissolved in the oil. Air forms bubbles in the oil. If the hydraulic support changes rapidly between high and low pressure in a very short time during the working process, the bubbles will generate high temperature on the high pressure side and burst on the low pressure side. If the hydraulic system components When there are pits and damage on the surface, the hydraulic oil will rush to the surface of the component at high speed to accelerate the surface wear and cause leakage.
②Particle pollution
Hydraulic cylinders are the main executive components of some construction machinery hydraulic systems. Because the piston rods are exposed and directly contact the environment during the working process, although the guide sleeve is equipped with dust rings and seals, it is inevitable to bring dust and dirt. Into the hydraulic system, it accelerates the scratches and wear of seals and piston rods, causing leakage, and particle contamination is one of the fastest factors for hydraulic component damage.
③Water pollution
Due to factors such as humid working environment, water may enter the hydraulic system. The water will react with the hydraulic oil to form acidic substances and sludge, reducing the lubricating performance of the hydraulic oil, accelerating the wear of components, and water will also cause the valve of the control valve. Sticking of the rod makes the control valve difficult to operate and scratches the seal, causing leakage.
④Part damage
The seal is made of oil-resistant rubber and other materials. The aging, cracking, and damage caused by long-term use will cause system leakage. If the parts are damaged by collision during work, it will scratch the sealing element and cause leakage.
Main leakage prevention measures
The factors that cause the leakage of the hydraulic system of construction machinery are the result of multiple comprehensive influences. With the existing technology and materials, it is difficult to fundamentally eliminate the leakage of the hydraulic system. Only from the above factors affecting hydraulic system leakage, reasonable measures should be taken to minimize hydraulic system leakage. The design and processing of the sealing groove should be fully considered in the design and processing links. In addition, the choice of seals is also very important. If the factors affecting leakage are not fully considered at the beginning, it will bring immeasurable losses to future production. Choose the correct assembly and repair methods, and learn from previous experience. For example, use special tools as much as possible in the assembly of the seal ring, and apply some grease on the seal ring. In the pollution control of hydraulic oil, we must start from the source of pollution, strengthen the control of pollution sources, and take effective filtering measures and regular oil quality inspections. In order to effectively cut off the pollution of the hydraulic cylinder by external factors (water, dust, particles, etc.), some protective measures can be added. In short, the prevention and control of leakage must be fully implemented and comprehensive considerations can be effective.
