The proactive maintenance strategy for hydraulic oil pumps involves monitoring and correcting the root causes of machine failures to maintain the basic parameters for normal machine operation within acceptable ranges. Therefore, the first step in implementing proactive maintenance for hydraulic oil pumps is to identify their root causes of failure.
Generally, machine failure refers to the inability of the machine's materials, structure, or system to achieve the expected performance under safe and normal conditions. Any abnormal operating condition that leads to material wear and performance degradation is called a "root cause of failure." When any root cause parameter of the system becomes abnormal (exceeding the allowable range), if corrective measures are not taken in time, it will cause material wear, leading to a decline in working performance and ultimately, complete machine failure. The failure development process is shown in Figure 18-2.
The main root causes of hydraulic oil pump failures are: liquid contamination, liquid leakage, changes in liquid chemical properties, changes in liquid physical properties, liquid cavitation, and liquid system overheating. To prevent the occurrence and development of hydraulic oil pump failures, it is essential to monitor and correct these root cause parameters to keep them within acceptable ranges. In other words, the stability of the root cause of failure must be maintained.
What are the root causes of hydraulic pump failure?
1. Hydraulic Oil Contamination
Hydraulic oil contamination is a major cause of hydraulic pump failure. Statistics show that approximately 75% of hydraulic pump failures are caused by hydraulic oil contamination. The main forms of component failure caused by hydraulic oil contamination include contamination wear, contamination jamming, and contamination blockage. The main factors affecting the wear and performance degradation of hydraulic component materials are the degree of hydraulic oil contamination, the component's contamination sensitivity, and operating conditions.
To prevent failures and malfunctions caused by hydraulic oil, contamination control measures must be implemented to keep the degree of hydraulic oil contamination within the critical component's contamination tolerance range, that is, to stabilize the degree of hydraulic oil contamination.
2. Leakage
Leakage is a common problem in current hydraulic pumps. External leakage occurs at the external mating surfaces of hydraulic components, pipe joints, and interfaces of linear and rotary motion. Internal leakage occurs at the clearances of internal moving parts of hydraulic components, such as the flow distribution pair of the hydraulic pump, and the sealing clearances between the hydraulic cylinder and piston. Excessive internal leakage reduces pump volumetric efficiency, causes hydraulic cylinder creep, and reduces hydraulic motor speed, posing a significant threat to hydraulic pumps.
Leakage is a signal of hydraulic pump failure and malfunction, requiring timely countermeasures. The main factors affecting hydraulic pump leakage are seal wear or damage, loosening of pipes due to vibration, and improper hose processing or installation. A reasonable sealing structure, excellent sealing materials, and sufficient sealing force are crucial factors for the stability of hydraulic oil leakage. Controlling the hydraulic pump's temperature rise, controlling oil contamination, and controlling excessive vibration can control both internal and external leakage.
3. Changes in the Chemical Properties of Hydraulic Oil
The chemical properties of hydraulic oil are related to its base components and the chemical composition of additives. To improve hydraulic oil performance to meet the operating requirements of hydraulic pumps, various chemical additives are added to the working fluid, such as antioxidants, rust removers, viscosity increasers, anti-wear agents, and low-pour-point additives. Therefore, maintaining chemical stability is essential for ensuring the reliable operation of hydraulic pumps and extending component lifespan.
Due to the high pressure and harsh environment within the system, the chemical composition and properties of hydraulic oil gradually change during operation and storage. This is mainly caused by the oxidation of the hydraulic oil and the consumption of additives. This oxidation reaction results in the deterioration of the hydraulic oil, producing soluble and insoluble compounds such as resins, acidic substances, and precipitates, further increasing the contamination of the hydraulic oil.
The rate of hydraulic oil deterioration is related to factors such as operating temperature, pressure, and the type and content of contaminants. When water and metal particles acting as catalysts are present simultaneously, the oxidation rate of the oil increases dramatically. Iron increases the oxidation rate by 10 times, and copper increases it by 30 times. Therefore, effectively controlling oil contamination and selecting oils with additive-stabilized properties helps maintain the chemical stability of the oil.
4. Changes in the Physical Properties of Hydraulic Oil
The main physical properties of hydraulic oil related to the hydraulic pump include viscosity, viscosity index, shear strength, bulk modulus of elasticity, saturated vapor pressure, air absorption, and water content. These physical properties vary with system conditions (such as pressure and temperature), the chemical composition of the hydraulic oil, mechanical agitation and shearing, and the type and concentration of contaminants.
Generally, once the influencing and interfering factors disappear, the physical properties of the hydraulic oil can return to their original values, at which point the hydraulic oil's physical properties can be considered stable. However, when the changes in the physical properties of the hydraulic oil exceed the allowable range, they will harm the system and components. Therefore, hydraulic pump maintenance personnel must pay attention to changes in the physical properties of the hydraulic oil and maintain its stability.
5. Cavitation
Cavitation in a hydraulic pump can cause vibration and noise, accelerate oil deterioration, and worsen the pump's performance.
6. Hydraulic Pump Overheating
The operating temperature of a hydraulic pump should be within a certain range. Excessively high temperatures reduce the viscosity of the hydraulic oil, worsen lubrication, increase leakage, and cause oxidation and decomposition of the hydraulic oil.
At excessively low temperatures, the viscosity of the hydraulic oil increases, and its fluidity deteriorates. Temperatures exceeding the allowable range also significantly affect the performance of sealing materials and components. At low temperatures, the flexibility of rubber elastomers decreases; at high temperatures, the material strength weakens, and thermal expansion can easily cause obstruction or jamming of component movement. Therefore, controlling excessive temperature fluctuations in hydraulic pumps is crucial.
