Cause analysis of oil leakage in hydraulic system
1. Oil leakage caused by the pollution of the hydraulic system
The pollution of hydraulic system will lead to the wear and tear of hydraulic components, the decline of sealing performance, the reduction of volumetric efficiency, and the internal and external leakage. The clearance of the moving pair of hydraulic components is generally 5 ~ 15µm. For the valve components, when the pollution particles enter the moving pair, the interaction scratches the surface, and cuts out the new abrasive particles, exacerbates the wear, so that the clearance is expanded, resulting in leakage or oil in the valve; In the case of pump components, contamination particles can cause the relative moving parts (the plunger and cylinder holes of the plunger pump, the cylinder block, and the valve plate. Vane pump blade tip and stator surface, etc.) wear is aggravated, causing the increase of the clearance, the increase of leakage, resulting in the pump volume efficiency is reduced; For the hydraulic cylinder, pollution particles will accelerate the wear of the sealing device, so that the leakage is significantly increased, leading to the reduction of power, but also make the cylinder or piston rod pulled and scrapped; For hydraulic catheters, pollution particles will aggravate the wear of the inner wall of the catheter, or even scratch the inner wall, especially when the flow rate of the liquid is high and unstable (fast flow rate and large pressure pulsation), which will lead to the impact of the material on the inner wall of the catheter and peel off, and eventually lead to the rupture of the catheter and oil leakage.
When the hydraulic oil contains water, it will promote the formation of emulsion hydraulic oil, reduce the lubrication and anti-corrosion effect of hydraulic oil, accelerate the wear and corrosion of hydraulic components and hydraulic pipe inner wall. When the hydraulic oil contains a large number of bubbles, the bubbles will be compressed in the high pressure area, and the surrounding oil will flow at a high speed to the space occupied by the bubbles, causing a strong hydraulic impact. Under the impact of the high pressure liquid mixture, the hydraulic components and the inner wall of the hydraulic pipe are corroded and spalling. These conditions will eventually cause the hydraulic components and hydraulic pipe damage and internal and external leakage.
2. Oil leakage caused by too high oil temperature
Hydraulic system temperature is generally maintained in 35 ~ 60℃ is the most appropriate, the highest should not exceed 80℃. Under normal oil temperature, the performance of hydraulic oil is good. The oil temperature is too high, can reduce the hydraulic oil viscosity, oil film thinning and easy damage, lubrication performance, mechanical wear, the volumetric efficiency is reduced, resulting in increased leakage within the hydraulic oil, leakage and wear and temperature in the system at the same time, the system temperature will increase leakage and wear, and even cause a vicious cycle, disable hydraulic components quickly; If the oil temperature is too high, the aging of rubber seal ring will be accelerated, and the sealing performance will be reduced, which will eventually lead to the failure of the seal and oil leakage; Oil temperature is too high, will accelerate the aging of rubber soft tubing, serious tubing hardening and cracking, such tubing under the action of high temperature, high pressure will eventually lead to tubing explosion and oil leakage. Therefore, the system oil temperature should be controlled to keep it in the normal range.
3. Oil leakage caused by poor pipeline quality
When repairing or replacing the hydraulic pipeline, if the inferior oil pipe is installed in the hydraulic system, because of its low bearing capacity and short service life, the use time will not be long and there will be oil leakage. The poor quality of hard tubing is mainly manifested in the uneven thickness of pipe wall, which reduces the bearing capacity. Inferior hose is mainly poor rubber quality, steel wire layer tension shortage, uneven weaving, so that the bearing capacity is insufficient, under the pressure of oil impact, easy to cause pipeline damage and oil leakage
4. Oil leakage caused by problems with oil seals
Oil seal is widely used in the sealing between moving parts and static parts (such as the seal of the shaft end of the gear pump, the seal of the shaft end of the hydraulic coupler, etc., are sealed by oil seal), there are many kinds of oil seal, but the sealing principle is basically the same. It can prevent the internal oil leakage, but also can prevent the outside dust, impurities into the hydraulic system.
Such as the quality of the oil seal itself is not qualified (the main problems are: the oil seal structure design is unreasonable, the oil seal material selection is improper, the oil seal manufacturing process is unreasonable or the dimension accuracy is poor, etc.), such an oil seal can not play a good sealing role, which leads to the leakage of oil; Oil seal service time is too long, beyond the service life, will be due to aging, loss of elasticity and wear and tear and lead to oil seal leakage; Oil seal assembly pressure is not in place, resulting in lip damage or scratch lip, and cause oil leakage; When installing the oil seal, the oil seal is not wiped clean or the oil seal dust retaining ring is damaged, resulting in sediment entering the oil seal working face, so that the oil seal loses the sealing effect by accelerating wear and tear at work, resulting in the leakage of oil.
5. Oil leakage caused by problems with hydraulic seals
In the assembly process, if the excessive stretch will make the seal lose elasticity, it will reduce the sealing performance; If in the assembly process, due to the flip of the seal and scratch the lip of the seal, it will lead to leakage; If the quality of the sealing groove or the sealing contact surface of the seal is poor, then the seal is installed in the sealing pair with low dimensional accuracy, low surface roughness and low shape position tolerance, which will lead to the damage of the seal, resulting in the leakage of hydraulic oil; If the seal is not properly selected, it will cause the leakage of hydraulic oil, for example, the sealing material selected in the high pressure system is too soft, so at work, the seal is easy to squeeze into the sealing gap and damage, resulting in hydraulic oil leakage; If the quality of the seal is poor, the pressure resistance is low, the service life is short, the sealing performance is poor, so that the seal is not long to use will produce leakage.
6. Oil leakage caused by improper assembly of hydraulic pipelines
(1) Hydraulic pipe bending is not good.
In the process of assembling hydraulic hard conduit, the pipe should be bent according to the specified radius, otherwise the pipe will produce different bending stress, and gradually produce leakage under the action of oil pressure. If the bending radius of the hard pipe is too small, it will lead to the thinning of the outer pipe wall and wrinkles of the inner pipe wall, so that there is a great internal stress in the bending part of the pipe, and the strength is greatly weakened. Under strong vibration or impact, the pipe is easy to produce transverse cracks and oil leakage; If there is a large ellipticity in the bending part, longitudinal cracks and oil leakage will easily occur when the oil pressure pulsates in the pipe. When installing the hose, if the bending radius does not meet the requirements or the hose is twisted, the hose will be damaged and leak oil.
(2) Pipeline installation and fixation do not meet the requirements.
Common improper installation and fixation are as follows.
① In the installation of tubing, regardless of the length, Angle and thread of tubing is appropriate to forcibly assemble, so that the pipeline deformation, installation stress, at the same time, it is easy to hit the pipeline, resulting in the reduction of its strength.
(2) When installing tubing, do not pay attention to fixing, tighten the bolts when the pipeline rotates together, causing the pipeline to twist or collide with other parts and produce friction, shortening the service life of the pipeline.
③ The pipe clip is sometimes too loose, so that the friction and vibration between the pipe and the clip is strengthened; Sometimes too tight, so that the surface of the pipeline (especially aluminum pipe or copper pipe) clamping deformation, these circumstances will make the pipeline damage and oil leakage.
(4) The tightening torque of the pipe joint seriously exceeds the provisions, so that the bell mouth of the joint is broken, thread strain, trip, resulting in serious! An accident with oil.
