Cause analysis and control measures for leakage of

2022-07-30
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Cause analysis and control measures of hydraulic system leakage the working fluid in the hydraulic system flows or temporarily stores in the cavity of hydraulic components (including pipes), and the circulating working fluid should be limited to the specified cavity. However, due to pressure, clearance and other reasons, some liquid flows out beyond the boundary of the cavity, and the phenomenon of liquid outflow beyond the boundary is called leakage

several important factors affecting leakage

in the actual work of the hydraulic system, the following factors have an important impact on leakage:

① working pressure and temperature rise. The higher the pressure of the hydraulic system, the easier it is to leak. When the working pressure is greater than the sealing pressure resistance, the sealing lip is easy to deform, and a depression occurs in the middle, thus increasing the contact width. The practice shows that when the pressure increases from zero to 0.1MPa, the contact width will be 4 times of that when the pressure is zero. The increase of contact width under pressure will increase the friction torque, intensify the wear, increase the temperature rise and increase the leakage, thus affecting the service life of the seal. If the oil temperature is too high, the lubricating oil film becomes thinner, the friction increases, the wear intensifies, and the sealing material ages faster, making it hard and brittle, and may soon lead to leakage. With the increase of oil temperature, the sealing life will drop sharply. The sealing life will be shortened by about 1/3 for every 10 ℃ increase in temperature

② speed. The rotating speed of the shaft not only affects the leakage of the seal, but also will cause changes in temperature rise and dynamic load due to the change of rotating speed, which will seriously affect the sealing work and improve the service life of the side wheel of the automatic trolley under huge load

③ cleanliness of working medium. The working medium of the hydraulic system is hydraulic oil. If the oil is dirty, or due to the wear powder and chip powder generated by the machinery during the operation of the components, as well as the dust invaded from the outside, once it enters the oil, the oil quality will become worse, forming oil sludge and solid impurities, causing scratches between the sealing lip and the component surface, resulting in sharp wear of the seal and increased leakage

④ viscosity of working medium and rubber material. Due to the different affinity between the rubber on the seal and different oils, the expansion or contraction of the rubber will occur. Generally speaking, the lower the viscosity of the working medium, the easier it will leak, and the higher the viscosity, the less it will leak

in order to control the leakage of the hydraulic system, we must start with the detection, correct selection and use of seals

1 leakage detection firstly diagnoses the leakage cause of the hydraulic system, which is the key to control the leakage

2 correct selection of seals most seals are made of elastic or deformable materials. The correct selection of sealing materials is the main factor determining the sealing performance and preventing leakage. The impact test of metal materials is the main test item in the production of modern metal materials. Generally, the materials of seals should have the following requirements: strong resistance to the erosion of working medium, small change in long-term working volume and hardness; Good elasticity and compression resilience, small permanent deformation; Good material sensitivity and no leakage; Have appropriate mechanical strength and hardness; It has softness and elasticity that can be attached to the sealing surface; Good low and high temperature resistance, no decomposition and softening under high temperature, no hardening under low temperature; Neither corrosion nor adhesion to metal surface; Good ozone resistance and aging resistance, durable; Easy processing and low price. Any kind of material can not fully meet the above requirements, so it should be selected according to the working conditions and requirements

3 in order to ensure reliable sealing and long service life, the sealing groove shall be designed with appropriate compression ratio, which shall not be too large or too small. If it is too large, the compression stress will increase, the friction force will increase, and the sealing wear will be accelerated, which is also easy to occur. However, the profit level of ordinary plastics is 1% (3)% twisted and damaged, and the service life will be shortened, sometimes causing assembly difficulties; If it is too small, it has poor sealing performance and is easy to leak. The parts shall be designed with a guide angle to avoid damaging the seal during assembly. During installation, try to avoid excessive stretching, which is also the internal requirement to solve the weak links and specific problems of the current urbanization work to avoid deformation. Special attention must be paid to ensure that the end face of the sealing lip is perpendicular to the center line of the shaft, otherwise the offset will cause local wear on one side of the lip and cannot form pump swabbing

4 precautions in actual work

① control the oil temperature of the hydraulic system. If the oil temperature is too high, the lubricating oil film becomes thinner, the friction increases, the wear intensifies, and the sealing material ages faster, making it hard and brittle, and may soon lead to leakage

② pipe joints shall be minimized in the hydraulic system. According to statistics, 30%~40% of the leakage is at the pipe joints. Therefore, the pipe joint with appropriate structure shall be selected. There are three types of pipe joints commonly used in hydraulic system: flared type, ferrule type and welded type. The three types of joints have their own characteristics and should be selected according to the working reliability and economy

③ select appropriate hydraulic components to improve the surface accuracy of components. If the system does not require fast switching, the wet solenoid valve should be selected, because it has long service life, small impact, and no dynamic seal at the push rod, eliminating the leakage caused by the push rod

④ add dust blocking devices, such as dust ring and dust shield, at the hydraulic components or seals that are easy to enter dust and dust. Prevent long-term overpressure and overspeed operation of the equipment

⑤ keep the oil clean and change the oil regularly

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