The hydraulic transmission system has the advantages of small size, light weight, large specific power, stable operation, and stepless speed regulation. It is widely used in various cranes. However, the transmission efficiency of the hydraulic transmission system is lower than that of other transmission systems, and it is easy to produce faults and it is difficult to analyze and eliminate the faults. Therefore, maintenance personnel are required to have certain basic knowledge of hydraulic systems.

Classification of leaks:

There are two main types of leakage in the hydraulic system of construction machinery: fixed seal leakage and movement seal leakage. The fixed seal leakage mainly includes the cylinder bottom and the joints of various pipe joints. The movement seal mainly includes the cylinder piston rod, 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 into the environment. Internal leakage refers to the existence of pressure differences between the high and low pressure sides and the failure of seals. Make the hydraulic oil flow from the high pressure side to the low pressure side inside the system.

3. Reasons affecting leakage:

(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, changes in ambient temperature, etc. These all directly or indirectly cause hydraulic system leakage to varying degrees. In addition, due to the 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, thereby causing leakage.

(2) Other 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 for the sealing ring is out of tolerance or due to processing problems, it is out of round, 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.

(2) Assembly factors:

The hydraulic components should be free from savage operations during assembly. Excessive force will cause the parts to deform, especially hitting the cylinder block and sealing flange 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 be easy to age and lose its original elasticity, thereby losing the sealing function.

(3) Oil pollution and damage to parts

(1) Gas 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.

(2) Particle pollution

The hydraulic cylinder is the main executive component of some construction machinery hydraulic systems. Because the piston rod is exposed and directly contacts 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 will accelerate the scratches and wear of the seals and piston rods, which will cause leakage. Particle pollution is one of the fastest factors in the damage of hydraulic components.

(3) Parts 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 collisions during work, the sealing elements will be scratched, causing leakage.