Leakage causes and Countermeasures of Hydraulic Systems in Construction Machinery

I. Preface

Leakage is a common fault phenomenon in hydraulic machinery at present, especially in the hydraulic systems of construction machinery, which is more serious. It is mainly caused by the pressure difference generated when the liquid flows in the hydraulic components and pipelines, as well as the gaps existing among the components. In addition, harsh working conditions can also have a certain impact on the sealing of construction machinery. Once a hydraulic system leaks, it will cause the system pressure to fail to be established. The leakage of hydraulic oil will also cause environmental pollution, affect production and even lead to incalculable serious consequences. The following is a brief discussion on the causes and countermeasures of leakage in some factors that affect the hydraulic system of construction machinery.

Ii. Classification of Leakage

There are mainly two types of leakage in the hydraulic system of construction machinery: leakage at fixed seals and leakage at moving seals. The leakage at fixed seals mainly occurs at the bottom of the cylinder, the connection points of various pipe joints, etc. The leakage at moving seals mainly occurs at the piston rod part of the cylinder, the valve stem of the multi-way valve, etc. The leakage of oil can also be classified 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 flow of hydraulic oil from the high-pressure side to the low-pressure side within the system due to the existence of pressure differences between the high and low pressure sides and the failure of sealing parts, etc.

Iii. Causes Affecting Leakage:

(1) Design factors:

Selection of seals

The reliability of a hydraulic system largely depends on the design of the system's seals and the selection of sealing components. Due to the unreasonable selection of sealing structures and non-compliance with standards in the design, the compatibility types of hydraulic oil and sealing materials, load conditions, ultimate pressure, working speed, and changes in environmental temperature have not been taken into account in the design. All of these directly or indirectly cause leakage in the hydraulic system to varying degrees. In addition, as the operating environment of construction machinery contains dust and impurities, appropriate dust-proof seals should be selected in the design to prevent dust and other contaminants from entering the system, damaging the seals and contaminating the oil, thereby causing leakage.

(2) Other design reasons

The design takes into account that the geometric accuracy and roughness of the moving surfaces are not comprehensive enough, and the strength check of the connection parts is not carried out in the design. All these can cause leakage during the operation of the machinery.

(II) Manufacturing and assembly factors

(1) Manufacturing factors

All hydraulic components and sealing parts have strict requirements for dimensional tolerances, surface treatment, surface finish and shape and position tolerances, etc. If the manufacturing process exceeds the tolerance, for instance, the piston radius of the oil cylinder, the depth or width of the sealing groove, the size of the hole for installing the sealing ring exceed the tolerance, or if it becomes out of circle due to processing issues, has burrs or depressions by itself, or the chromium plating falls off, etc., the sealing part will deform, be scratched, be crushed or not pressed tightly, thus losing its sealing function. This will cause the parts themselves to have inherent leakage points, and leakage may occur after assembly or during use.

(2) Assembly factors:

During the assembly of hydraulic components, rough handling should be strictly avoided. Excessive force can cause deformation of the parts, especially when hitting the cylinder body, sealing flanges, etc. with copper rods or the like. Before assembly, the parts should be carefully inspected. During assembly, the parts should be dipped in a little hydraulic oil and gently pressed in. When cleaning, diesel should be used, especially for rubber components such as sealing rings, dust-proof rings, and O-rings. If gasoline is used, it will cause them to age easily and lose their original elasticity, thus losing their sealing function.

(3) Oil contamination and damage to components

(1) Gas pollution

Under atmospheric pressure, about 10% of air can be dissolved in hydraulic oil. Under the high pressure of the hydraulic system, more air or gas will dissolve in the oil. Air forms bubbles in the oil. If the pressure of the hydraulic support changes rapidly between high and low pressure within an extremely short period of time during operation, the bubbles will generate high temperatures on the high-pressure side and burst on the low-pressure side. If there are depressions and damages on the surface of the components in the hydraulic system, the hydraulic oil will rush towards the surface of the components at high speed, accelerating surface wear and causing leakage.

(2) Particle contamination

As the main actuating component of some construction machinery hydraulic systems, the hydraulic cylinder, due to the exposed piston rod directly in contact with the environment during operation, although dust-proof rings and seals are installed on the guide sleeve, it is still inevitable that dust and dirt will be brought into the hydraulic system, accelerating the scratches and wear of the seals and piston rods, and thus causing leakage. Particle contamination is one of the fastest factors causing damage to hydraulic components.

(3) Water pollution

Due to the influence of factors such as a humid working environment, water may enter the hydraulic system. Water will react with the hydraulic oil to form acidic substances and sludge, reducing the lubricating performance of the hydraulic oil and accelerating the wear of components. Water can also cause the valve stem of the control valve to stick together, making the operation of the control valve difficult and scratching the sealing parts, resulting in leakage.

(4) Part damage

Seals are made of materials such as oil-resistant rubber. Due to long-term use, aging, cracking, and damage can all cause system leakage. If the parts are damaged by collision during operation, the sealing elements will be scratched, thus causing leakage.

Iv. Main Prevention and Control Measures for Leakage

The factors causing leakage in the hydraulic system of construction machinery are the result of the combined influence of multiple aspects. With the current technology and materials, it is very difficult to eliminate the leakage of the hydraulic system fundamentally. Only by starting from the above factors that affect the leakage of the hydraulic system and taking reasonable measures can the leakage of the hydraulic system be reduced as much as possible. In the design and processing stages, the important factors affecting leakage should be fully considered in the design and processing of sealing grooves. In addition, the selection of sealing parts is also very important. If the influencing factors of leakage are not comprehensively considered at the beginning, it will bring incalculable losses to the subsequent production. Choose the correct assembly and repair methods and draw on past experience. For instance, when assembling the sealing ring, it is advisable to use dedicated tools as much as possible and apply some grease to the sealing ring. In terms of pollution control of hydraulic oil, it is necessary to start from the source of pollution, strengthen the control of pollution sources, and also take effective filtration measures and regular oil quality inspections. To effectively cut off the contamination of hydraulic cylinders by external factors (such as water, dust, particles, etc.), some protective measures can be added. In conclusion, the prevention and control of leakage should be carried out comprehensively and with a comprehensive consideration to achieve effective results.