The fully hydraulic drive system is one of the main working mechanisms in construction machinery. In practical applications, there may be phenomena such as slow movement of hydraulic system execution components, weak drive, and overall poor operation of the mechanism. It is difficult to determine the specific damaged components only by inspecting the appearance. Therefore, it is necessary to understand and master the occurrence rules of hydraulic system faults in construction machinery, and do a good job in maintenance and management of the hydraulic system in order to accurately analyze the causes of faults and improve the efficiency of fault elimination. This article mainly analyzes the diagnosis and troubleshooting of common faults in hydraulic transmission systems of construction machinery.
Analysis of the Causes of Hydraulic System Malfunctions
No matter what kind of malfunction occurs in the hydraulic system, the main reasons are mainly as follows: firstly, the components in the circuit themselves have poor operation, the system circuit interferes with each other, or a single component has abnormal operation. According to relevant statistical data, the hydraulic oil pump is one of the components with a high failure rate among all hydraulic components. Secondly, improper selection of working media and poor management can lead to mechanical failures. It can be said that during the operation of hydraulic systems, system failures caused by hydraulic oil pollutants account for 70% to 80% of the total failure rate, and hydraulic oil failures are mostly mechanical failures caused by oil impurities, such as small particle pollution that can wear down oil pumps, scratch valves, or cause blockage of throttle valves and valve holes. Improper installation and adjustment of the hydraulic system can also lead to system failures. For example, if the bending radius of the pipe and the distance between the bending point and the pipe are too small during pipeline installation, it will reduce the system's pressure resistance.
General steps for diagnosing hydraulic system faults
Hydraulic system fault diagnosis steps
The malfunction of the hydraulic system may be caused by a problem with a certain component, so it is necessary to follow certain steps to identify the faulty component and further troubleshoot the problem. The specific steps are as follows:
Observe the operation of the transmission equipment to see if there are any issues such as poor motion stability, incorrect motion direction, inconsistent motion speed with requirements, disordered action sequence, severe leakage, or crawling. However, regardless of the cause, the problem can be identified from three aspects: flow rate, pressure, and direction. The second step is to review the hydraulic diagram, comprehensively inspect each hydraulic component to ensure its normal performance, and make a preliminary judgment on its quality condition. The third step is to analyze the fault by listing the relevant components of each phase and analyzing them one by one, taking care not to miss any components that have a significant impact on the fault. Step four, after listing the list of fault related components, they should be sorted, and the components that need to be inspected and their key inspection parts should be listed one by one. If necessary, they should be tested using measuring instruments. The fifth step is to check the key components in the initial inspection checklist, including the applicability of component application and assembly, the applicability of component measuring devices and testing methods, the applicability of external signals of components, and whether they respond to external signals normally; Excessive component temperature, vibration, leakage, noise, etc. are all precursors to the failure of certain components, and special attention should be paid. Step six, if the fault is determined by the initial inspection method, then use the instrument to repeatedly test until the fault point is found. The seventh step is to promptly repair or replace the faulty component after identifying it. Step 8: After troubleshooting the faulty component and before restarting the host, a comprehensive analysis of the cause and consequences of the fault should be conducted. If contamination or high oil temperature causes the fault to occur, it may affect other components, so further troubleshooting is necessary.
Hydraulic system restart steps
After troubleshooting the hydraulic system according to the above steps, it is not allowed to blindly restart the system. The following restart procedures must be followed to further prevent new faults from occurring. The specific restart procedures are as follows: first, confirm that the fault has been eliminated, further check whether pollutants have entered the system, and if contaminated, clean the system in a timely manner; Secondly, check the correctness of component installation. If it is incorrect, replace or reinstall it; Thirdly, check the correctness of hydraulic pipelines and circuit connections. If there are any errors or omissions, reinstall and reconnect them; Fourth, check if there are any components that need to be adjusted in safe startup mode; Fifth, check the oil in the oil pump and motor, and replenish the oil in a timely manner if it is not full; Sixth, check if the system requires oil drainage, and if necessary, promptly drain the oil; Check the installation of all safety interlock devices; After Z, all staff members believed that the system could be restarted before conducting a trial run.
Examples of Fault Diagnosis and Troubleshooting for Hydraulic Systems in Construction Machinery
The hydraulic system of a certain loader converts energy between steering and operation. During daily operation, the equipment often experiences faults such as weak lifting of the boom, weak retraction of the bucket, excessive settlement of the boom hydraulic cylinder, and failure to move. Therefore, a series of inspections were conducted on the hydraulic system. Taking the example of weak lifting of the boom, the diagnosis and elimination of hydraulic system faults are analyzed and explained below
Fault diagnosis
The reason why the loader has weak lifting of the boom may be due to insufficient pressure and oil pressure at the piston end of the boom hydraulic cylinder. The main reasons for this problem include the following two aspects: one is due to clogged oil filters or serious internal leaks in the hydraulic pump, resulting in insufficient oil pressure pumped out by the oil pump. On the other hand, due to the serious leakage of the hydraulic system itself, including internal and external leakage, there are many reasons for hydraulic system leakage, such as the total safety valve pressure of the multi way directional valve being too low, debris jamming the opening position of the main valve core, excessive clearance between the boom directional valve stem and the valve body hole in the dynamic circuit valve, severe damage to the sealing ring on the boom hydraulic cylinder piston, sealing failure of the one-way valve inside the valve, and large clearance between the flow conversion valve core and the valve body.
Troubleshooting
First, check the filter, clean it promptly if it is clogged, and replace it if it cannot be thoroughly cleaned; If the oil is found to have deteriorated, it should be replaced completely; Conduct a comprehensive inspection of the main safety valve. If it gets stuck, remove it and carefully clean the main valve core until it can be freely pushed. If the fault cannot be eliminated after cleaning, the multi way directional valve can be further operated and the pressure regulating nut of the main safety valve can be rotated. If the system pressure can reach the specified value, it proves that the fault has been basically eliminated. Secondly, check if the sealing ring of the hydraulic cylinder piston has failed. The inspection method is as follows: retract the boom hydraulic cylinder to the bottom, then remove the high-pressure hose at the outlet joint of the large chamber, operate the multi way valve boom steering handle to retract the piston rod of the boom hydraulic cylinder, and then observe the position of the hydraulic cylinder large chamber outlet. If the oil flows out at this location and forms an oil flow greater than 30mL/min, it proves that the sealing ring has failed and can only be replaced; If only a small amount of oil seeps out from the outlet of the large chamber of the hydraulic cylinder, it proves that the sealing effect of the piston small sealing ring is good, and further inspection is needed. Once again, whether the gap between the valve stem and the valve body hole is too large can be determined by observing the usage time of the multi way valve. The normal gap between the valve stem and the valve body hole must be controlled between 0.01mm-0.04mm. If it exceeds this range, it indicates that the gap is too large. Next, check the flow conversion valve again. If the gap between the valve core and the valve body exceeds 0.04mm, it indicates that the gap between the two is too large and needs to be replaced in a timely manner. In addition, the sealing performance of the contact surface between the one-way valve and the valve seat inside the valve stem should be checked. If there is a poor sealing phenomenon, the valve core should be replaced in a timely manner; Further inspect the spring and promptly replace any deformed, softened, or broken springs. After Z, if the above steps still cannot eliminate the fault, the hydraulic pump should be removed for inspection. The loader uses a CBG type hydraulic pump, which mainly checks the end face clearance and the meshing clearance between the two meshing gears, as well as the radial clearance between the gear and the housing. If it exceeds the normal value, it indicates excessive internal leakage and needs to be replaced.
Strengthen the operation and maintenance of hydraulic systems in construction machinery
The hydraulic system is very important in construction machinery, so it is necessary to strengthen daily operation and maintenance to extend its service life and reduce the failure rate. Therefore, the following aspects of work should be done well: firstly, construction machinery should not be operated roughly during operation to avoid generating impact loads and increasing the failure rate. It should be noted that due to the varying degrees of free play in the operating system of each device, operators need to maintain stability, adjust their control actions, gradually adapt to the operating personality of the device, and cultivate good operating habits. Secondly, the working temperature of the hydraulic system should be reasonably controlled, and the temperature of the hydraulic oil should not be too high, otherwise it will reduce the viscosity of the hydraulic oil and cause leakage; Reduce the strength of the lubricating oil film and accelerate mechanical wear; In addition, excessive hydraulic oil temperature can generate carbides and sludge, deteriorate oil quality, and accelerate the aging of components such as oil seals and high-pressure hoses. After Z, if the hydraulic system uses a pressure type hydraulic oil tank, it is necessary to closely monitor the air pressure of the oil tank to ensure that it is within the standard range specified in the random user manual. Otherwise, if the oil tank pressure is too low, it will cause insufficient oil suction of the oil pump; On the contrary, excessive pressure can cause oil leakage in the hydraulic system, and even lead to low-pressure oil circuit bursting.
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2025-04-15