Hydraulic seal: hydraulic system leakage causes and leakage measures

In hydraulic system, leakage affecting product quality is a problem that must be considered. For example, hydraulic cylinder, serious leakage will not only pollute the environment around the equipment, but also reduce the pressure of the hydraulic cylinder studio, so that the hydraulic cylinder can not work properly. Adopting more advanced methods to effectively prevent leakage and make the hydraulic system achieve "zero leakage" is the goal of the hydraulic industry for many years. In addition, accurate analysis of the causes of leakage of the hydraulic system can help us eliminate the leakage failure of the hydraulic system in time.

Hydraulic transmission has the following advantages:

The pipeline can transport the working liquid to any location;

The arrangement of the actuator is not limited by the orientation, and the transmission device is convenient and flexible with the help of the tubing connection.

Hydraulic transmission can convert the rotating motion of the prime mover into linear motion.

Stepless speed regulation can be realized easily;

Load control, speed control and direction control are easy to realize, and also easy to carry out centralized control, shaking control and automatic control;

Hydraulic transmission stability without vibration;

Good wetting conditions can improve the reliability and service life of hydraulic parts;

Hydraulic components are conducive to standardization, serialization and generalization. Therefore, hydraulic transmission has been widely used in various sectors of the national economy.

But hydraulic transmission also has some drawbacks:

Fluid flow resistance loss, oil leakage and mechanical friction, low efficiency;

High requirements for controlling working temperature;

Due to the leakage and compressibility of the working liquid, the stiffness of the hydraulic system is poor, and it is difficult to ensure a strict transmission ratio.

Very strict requirements for the use and maintenance of working fluids;

The cost of hydraulic parts is higher;

Hydraulic systems are difficult to judge and deal with failures, requiring employees to have a high level of technology and professional knowledge. Among them, working liquid leakage has always been an inevitable problem, and its solution is also one of the focuses of research in all walks of life.

Leakage control measures

The leakage factors of hydraulic system of construction machinery are the result of comprehensive influence of many aspects. With existing technology and materials, it is difficult to remove leakage from the hydraulic system at source. Only from the above factors affecting the leakage of hydraulic system, can we take reasonable countermeasures to reduce the leakage of hydraulic system as far as possible.

(1) The design and processing of sealed pipes must consider the key factors affecting leakage. The Society of Automotive Engineers (SAE) recommends two ways to avoid oil leaks:

SAE Straight thread "SAE" O "ring oil hole: seal" O "ring, connect straight thread;

SAE4 bolt flange: Suitable for large oil holes. In addition, the choice of seals is also very important, the roughness of the sealing surface is generally Ra3.2 ~ Ra1.6, and the dynamic sealing surface is Ra0.8 ~ Ra0.4. If the influence factors of leakage are not fully considered at the beginning, it will bring immeasurable losses to the future production.

(2) In terms of hydraulic oil pollution control, it is necessary to start from the source of pollution, strengthen the control of pollution sources, take corresponding filtration measures and regular oil quality testing. In order to effectively cut off the pollution of external factors (water, dust, particles, etc.) to the hydraulic cylinder, some protective measures can be taken.

(3) Installation. Before installing the hydraulic system, test the compressive performance of the equipment and check whether there is external leakage on the surface of each joint of the components. In case of leakage, effective measures should be taken. Only after all components do not leak can they be formally put into the system. When assembling hydraulic components and hydraulic systems, they should be strictly cleaned, burrs and welds removed, and corresponding anti-rust treatment, and installed in strict accordance with assembly process standards to avoid gap distortion caused by installation and gap abrasive caused by burrs, welding slag and rust.

(4) Reduce hydraulic shock. Common methods are:

Minimize the system start, stop and commutation frequency;

For hydraulic systems requiring frequent reversing, try to use reversing valves with dampers;

The energy accumulator is set in front of the control valve to reduce the transmission distance of shock wave and alleviate the hydraulic shock;

Increase the diameter of the pipe, shorten the length of the pipe as much as possible or use rubber pipes;

Set the safety valve, when the system pressure increases, can play the role of pressure relief, reduce the pressure impact.

(5) The machine is easy to leak in the running-in period, because it is difficult to find partial forging, processing and other defects in the assembly adjustment process, but due to the vibration and shock in the operation process, attention should be paid to the leakage in the running-in period, and timely discovery and treatment.

(6) From a technical point of view, new oil seals are being produced overseas, equipped with leakage sensors to detect seals (rotary seals); The main shaft pneumatic seal has the advantages of friction seal and labyrinth seal. U-shaped rubber parts composed of V-shaped torsion spring hydraulic system "flooding seal" and other types of combined seals, can be used for pressure 45MPa.

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