Exploring the causes and countermeasures of hydraulic system leakage
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Three leaks (oil leakage, water leakage, air leakage) are the current ills of machinery, especially the leakage of hydraulic equipment in dock equipment is more common. Mainly due to the pressure difference between the oil flowing in the hydraulic components and the pipeline and the gap between the components, causing leakage. Serious leakage of the hydraulic system will cause the system pressure to fail to build up, affecting the safety of the equipment, causing poor machine appearance, environmental pollution, increasing production costs and reducing productivity. Therefore, hydraulic system leakage must be controlled.
I. Leakage classification There are two main types of leakage of mechanical equipment hydraulic system; leakage at the fixed seal and leakage at the movement seal. The leakage at the fixed seal mainly includes the bottom of the cylinder and the joint of each joint. The sports seal mainly includes the cylinder piston rod and the multi-way valve stem. The leakage from the oil can also be divided into external leakage and internal leakage. The external leakage is mainly caused by the leakage of hydraulic oil from the system to the 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 presence of a pressure difference between the high and low pressure sides and the failure of the seal.
Second, the cause of leakage (a) design factors (1) the choice 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 selection of the seal structure in the design, seal The selection of the parts is not in accordance with the specifications. The compatibility of the hydraulic oil and the sealing material, the load condition, the ultimate pressure and the working speed are not considered in the design, which directly or indirectly cause the leakage of the hydraulic system to varying degrees. In addition, due to the dust and impurities in the environment of the machine, a suitable dust-proof seal should be selected in the design to prevent dust and other contaminants from entering the system to damage the seal and contaminate the oil, thereby causing leakage.
(2) Hydraulic shock and vibration Long-term hydraulic shock and vibration caused by loose joints can also cause leakage. This is a fault we often encounter.
(II) Manufacturing and assembly factors (1) Manufacturing factors: All hydraulic components and sealing components have strict dimensional tolerances, surface treatment, surface roughness and shape tolerances. If the manufacturing process is out of tolerance, for example: the piston radius of the cylinder, the depth or width of the sealing groove, the hole size of the sealing ring is too poor, or the machining is caused by the problem of rounding, burrs or pits, chrome peeling, etc. The piece will be deformed, scratched, crushed, or pinched, causing it to lose its sealing function. The part itself will have a congenital point of leakage, which will leak after assembly or during use.
(2) Assembly factors: Hydraulic components should be eliminated from rough operation during assembly. If excessive force is applied, the parts will be deformed, especially with copper rods, etc.; the parts should be carefully inspected before assembly. The part should be pressed with a little hydraulic oil and gently pressed in. When cleaning, apply diesel oil, especially rubber components such as seal ring, dust ring, O-ring, etc. If it is gasoline, it will be easy to age and lose its original elasticity, thus losing the seal. function.
(III) Wear and damage of dynamic seals Dynamic seals are generally made of oil-resistant rubber materials, which will age and crack when used for a long time. Abrasives, dust, impurities in the oil, the movement of the dynamic seal, over time, will also accelerate the aging and damage of the seal. If the part is damaged by a collision during work, the seal will be scratched. These conditions are the most likely to cause internal leakage.
(IV) Environmental impact The hydraulic cylinder is the main actuator of the mechanical hydraulic system. Because the piston rod is exposed directly to the environment during the working process, although the dustproof ring and the seal are installed on the guide sleeve, it is inevitable to dust and dirt. The material is brought into the hydraulic system to accelerate the scratching and wear of the seals and piston rods, causing leakage. The working environment is humid, which may cause water to enter the hydraulic system. The water will react with the hydraulic oil to form acidic substances and sludge, reduce the lubricating performance of the hydraulic oil, accelerate the wear of the parts, and the water will cause the valve stem of the control valve to bond. It is difficult to manipulate the control valve to scratch the seal and cause leakage. For every 10 °C increase in temperature, the seal life is halved and the optimum oil temperature is below 65 °C. Otherwise the seal will deteriorate prematurely. At atmospheric pressure, about 10% of the air can be dissolved in the hydraulic oil. Under the high pressure of the hydraulic system, more air is dissolved in the oil. Air forms bubbles in the oil. If the pressure changes rapidly between high and low pressure in a short period of time during hydraulic operation, the bubble will generate high temperature on the high pressure side and burst on the low pressure side if the component surface of the hydraulic system When there are pits and damage, the hydraulic oil will rush toward the surface of the component to accelerate the wear of the surface, causing leakage.
The main prevention and control measures for leakage shall ensure the geometric accuracy of each component in the design and processing steps; correctly select the seals; reduce the impact vibration: absorb the shock absorber, use the accumulator as much as possible, and properly use the pressure control valve to protect the system components. Install the pipe joints and replace the pipes with oil return blocks. Choose the correct assembly and repair method; find that the hydraulic components are damaged in time, especially when the piston rod and cylinder are damaged, the seal is most likely to be affected. In addition, special tools are used in the assembly of the seal and a little on the seal. grease. In the control of the working environment of the hydraulic system, it is necessary to start from the source of pollution, and it is possible to periodically test the oil quality, clean the filter device and the fuel tank, and cut off the pollution of hydraulic components by external factors (water, dust, particles, etc.). To prevent excessive oil temperature, a forced cooling device can be provided. In short, the leakage factor of the hydraulic system of mechanical equipment is multi-faceted. Only from the factors affecting the leakage of the hydraulic system, comprehensive consideration and reasonable and effective measures are taken to minimize leakage.
