1. Characteristics of hydraulic system faults in forklifts
1.1 Initial use of forklifts
In the early stages of use, the hydraulic system failure rate of newly manufactured forklifts is usually relatively high, which may be due to poor forklift quality, inappropriate component selection, or design problems with the forklift itself. The hydraulic system failure symptoms during the initial use of forklifts are usually: unstable system pressure, large vibration, high temperature rise, leakage, and unstable movement of actuating components.
1.2 Mid stage of forklift operation
At this stage, the probability of forklift failure is the lowest throughout the entire operation of the forklift, and most of the failures in this stage are caused by a decrease in the quality of hydraulic oil. There are impurities in the hydraulic oil that block the throttle holes of the hydraulic system, resulting in a decrease in its working performance. If the working performance of the safety valve and relief valve is unstable, it will increase the resistance of the slide valve in the hydraulic system, and also cause the mechanism to react slowly.
1.3 Late stage of forklift operation
In the later stage of forklift operation, hydraulic components wear out severely, seals fail and age, leading to a gradual increase in forklift failures. The fault phenomena in the later stage of forklift operation generally manifest as sluggish movement, decreased overall system efficiency, and increased leakage.
2. On site diagnosis methods for hydraulic system faults
There are usually two methods for diagnosing hydraulic system faults: one is to use inspection instruments for diagnosis. This method has not been widely used yet because its use is subject to significant limitations, mainly due to economic and technological constraints. Another method is computer-aided testing. This method is expensive, the testing equipment is expensive, and the operation is relatively complex. Therefore, we believe that the empirical logic method is ideal for diagnosing hydraulic system faults, which includes the following steps: (1) understanding the usage of forklifts. This is done to analyze the occurrence of faults, and the relevant situation of forklifts can be understood by asking the operator. If the hydraulic system of the forklift can operate, the fault maintenance personnel can personally observe the fault situation. (2) Analyze the structural working principle of hydraulic systems. Conduct a detailed analysis of its schematic diagram, familiarize oneself with the working principles, structures, and characteristics of each component, and analyze and determine the cause of the fault based on the fault symptoms. (3) Adopt reasonable inspection measures. Apply visual observation to analyze the causes of system failures. Check the operation of the components and the height of the oil level to see if they are normal and if there are any abnormal situations. (4) Use exclusion method for judgment. By following the above three steps, possible faulty components and their causes can be diagnosed, and then the troubleshooting method can be used for judgment. Firstly, identify or eliminate relatively simple faults, and then use the replacement method to conduct tests by replacing components of the same specifications that may cause faults.
3. Maintenance requirements for forklift hydraulic system
3.1 Prevent water and air from entering the hydraulic system
Excessive moisture in hydraulic oil can cause corrosion and wear to components and machinery. Pay attention to tightening the lid of the oil storage tank and placing it upside down when not in use. During maintenance, attention should be paid to preventing moisture from entering, and hydraulic oil with high moisture content should be filtered multiple times. At normal temperature and pressure, the air content in hydraulic oil is about 8%. When the pressure decreases, air in the oil will free up, causing cavitation of hydraulic components and generating noise, resulting in adverse consequences such as crawling of actuator components and decreased work efficiency.
3.2 Reasonable selection of hydraulic oil
Hydraulic oil plays a role in transmitting pressure, lubricating, cooling, and sealing in hydraulic systems. Improper selection of hydraulic oil is the main reason for early failures and reduced durability of hydraulic systems. Hydraulic oil plays an important role in hydraulic systems, such as sealing, pressure, and cooling. The main reason for the decrease in durability and early failure of hydraulic systems is improper selection of hydraulic oil. The selection of hydraulic oil should be carried out in accordance with the relevant provisions in the manual. In special circumstances, such as the need to use substitute oil, the selected hydraulic oil should have the same performance as the original brand as much as possible.
3.3 Preventing debris from entering the hydraulic system
Clean hydraulic oil has a significant impact on the working condition of hydraulic systems. There are many precision components in hydraulic systems, some of which are equipped with gaps or damping holes. Once impurities are mixed into the system, it will cause phenomena such as precision components jamming, pulling, and oil passage blockage, which will have a serious impact on the safe operation of the hydraulic system.
3.4 Precautions for Regular Maintenance
Regular maintenance precautions mainly include the following aspects: (1) 250h inspection. Remove the attachments on the filter screen. If there is excessive metal powder, it indicates the presence of hydraulic cylinder pulling or hydraulic pump wear. (2) 500 hour inspection. Due to minor damage to the filter element that is difficult to detect with the naked eye, it should be replaced regardless of its condition. If high-temperature operations are carried out for a long time, the filter element should be replaced in advance. (3) 1000h inspection. The hydraulic oil and filter element should be replaced, and the hydraulic oil tank and filter should be cleaned. If high-temperature operations are carried out for a long time, it is necessary to change the oil appropriately in advance. (4) Check at 7000h and 10000h. The hydraulic motor and hydraulic pump must undergo major repairs after 10000 hours of operation, and the hydraulic system must be maintained and adjusted by professionals as necessary.
4. Precautions for using forklifts
4.1 Homework should be done gently
Forklift operations should avoid rough handling, otherwise it will generate impact loads, causing frequent forklift failures and greatly shortening its service life. The impact load generated during operation can cause early wear, fracture, and breakage of the forklift mechanical structure, as well as the generation of impact pressure in the hydraulic system, resulting in damage to hydraulic components. The premature failure of oil seals and high-pressure oil pipe joints and rubber hoses can lead to oil leakage or pipe bursting, and frequent operation of relief valves can cause oil temperature to rise.
4.2 Pay attention to cavitation and overflow noise
Always pay attention to the sound of the hydraulic pump and relief valve during homework. If there is cavitation noise in the hydraulic pump, the cause should be identified and the fault should be eliminated before use. If a certain actuator moves slowly when there is no load and there is a sound of overflow valve overflow, it should be stopped immediately for maintenance.
4.3 Strictly implement the handover system
When the handover driver parks the forklift, it is necessary to ensure the safety and convenience of the incoming driver to inspect the forklift. The inspection includes checking whether the hydraulic system is leaking, whether the connections are loose, whether the piston rod and hydraulic hose are damaged, whether the low-pressure inlet pipe connection of the hydraulic pump is reliable, and whether the oil level in the hydraulic oil tank is correct. In addition, the atmospheric pressure hydraulic oil tank also needs to check and clean the vent holes to keep them unobstructed, in order to prevent the blockage of the vent holes and the occurrence of a certain degree of vacuum in the hydraulic oil tank, which may cause difficulty or damage to the hydraulic pump oil suction.
4.4 Maintain appropriate hydraulic oil temperature
The working temperature of hydraulic systems is generally controlled between 30 ℃ and 80 ℃. Excessive oil temperature in hydraulic systems can lead to the following problems: reduced viscosity of hydraulic oil, easy leakage, and decreased efficiency; The decrease in lubricating oil film strength accelerates mechanical wear; Generate carbides and sediment; Accelerated oxidation of oil and deterioration of oil quality; Premature aging of oil seals and high-pressure hoses.
Pay attention to the pressure of the pressure type hydraulic oil tank at all times during work, and its pressure must be maintained within the range specified in the "User Manual". When the pressure is too low, the hydraulic pump is prone to damage due to insufficient oil suction, and when the pressure is too high, it can cause oil leakage in the hydraulic system, which can easily lead to low-pressure oil circuit bursting.
5. Conclusion
The analysis and daily maintenance of hydraulic system faults in forklifts involve a complex system engineering process. Therefore, in the actual operation process, strict control should be exercised over each link to extend the service life of the forklift and improve the reliability of the forklift hydraulic system.
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