Hydraulic System Troubleshooting Principles

Correct analysis of faults is the premise of troubleshooting. Most system faults do not occur suddenly, and there are always signs before they occur. When the signs develop to a certain extent, failures will occur. There are various reasons for the failure, and there is no fixed rule to be found. Statistics show that about 90% of the failures in the hydraulic parts are caused by poor use and management. To diagnose failures quickly, accurately, and conveniently, it is necessary to fully understand the characteristics and laws of hydraulic failures, which is the basis of the failure diagnosis.

General principles

(1) First of all, to determine whether the working conditions and peripheral environment of the hydraulic system are normal, it is necessary to first find out whether it is the failure of the mechanical part or electrical control part of the equipment, or the failure of the hydraulic system itself, and at the same time, check whether the various conditions of the hydraulic system are in line with normal operation. Require.

(2) Regional judgment Determine the area related to the fault according to the fault phenomenon and characteristics, gradually narrow down the scope of the fault, detect the components in this area, analyze the cause, and finally find out the specific location of the fault.

(3) Grasp the types of faults and conduct a comprehensive analysis. According to the final phenomenon of the fault, gradually find out a variety of direct or indirect possible causes. To avoid blindness, comprehensive analysis and logical judgment must be carried out according to the basic principles of the system to reduce suspects. Approach step by step, and finally find the fault location.

(4) When verifying the possible cause of the failure, generally start from the most likely cause of the failure or the easiest place to check, which can reduce the workload of assembly and disassembly and improve the speed of diagnosis.

(5) Fault diagnosis is based on operation records and certain system parameters. Establish system operation records, which is the scientific basis for preventing, discovering, and dealing with failures; establish an equipment operation failure analysis table, which is a high-level summary of operating experience, which is helpful to quickly make judgments on failure phenomena; have certain detection methods, which can make an accurate quantitative analysis of faults.

Troubleshooting method

1. The traditional method of finding hydraulic system faults daily is to gradually approach the fault by logical analysis.

The basic idea is a comprehensive analysis and conditional judgment. That is, the maintenance personnel can judge the cause of the failure by experience by observing, listening, touching, and simple tests and understanding of the hydraulic system. When a hydraulic system fails, there are many possible sources of failure. Using the method of logic algebra, list the possible causes of failure, and then make logical judgments one by one according to the principle of first easy and then difficult, and approach one by one, and finally find out the cause of the failure and the specific conditions that cause the failure.

In the process of fault diagnosis, maintenance personnel is required to have basic knowledge of hydraulic systems and strong analytical capabilities to ensure the efficiency and accuracy of diagnosis. However, the diagnosis process is cumbersome, it must go through a lot of inspection and verification work, and it can only be analyzed qualitatively, and the fault cause of the diagnosis is not accurate enough. To reduce the blindness and experience of system fault detection and the workload of disassembly and assembly, traditional fault diagnosis methods are far from meeting the requirements of modern hydraulic systems. With the development of the hydraulic system towards large-scale, continuous production and automatic control, a variety of modern fault diagnosis methods have emerged. For example, demography can determine the number, shape, size, composition, and distribution of various abrasive particles separated from the oil, to timely and accurately determine the wear position, form, degree, etc. of the components in the system. Moreover, quantitative pollution analysis and evaluation of hydraulic oil can be carried out to achieve online detection and fault prevention.

Expert diagnosis system based on artificial intelligence, which simulates the problem-solving method of experienced experts in a certain field by computer. The fault phenomenon is input into the computer through the man-machine interface, and the computer can calculate the cause of the fault according to the input phenomenon and the knowledge in the knowledge base, and then output the cause through the man-machine interface, and propose maintenance plans or preventive measures. These methods bring broad prospects to hydraulic system fault diagnosis and lay a foundation for the automation of hydraulic system fault diagnosis. However, most of these methods require expensive testing equipment and complex sensing control systems, and computer processing systems. Some methods have certain difficulties in the research and are generally not suitable for field promotion. The following introduces a simple and practical hydraulic system fault diagnosis method.

2. Fault diagnosis system based on parameter measurement

Whether a hydraulic system works normally depends on whether two main working parameters, namely pressure, and flow rate, are in normal working condition, and whether parameters such as system temperature and actuator speed are normal or not. The failure phenomenon of the hydraulic system is various, and the cause of the failure is also a combination of various factors. The same factor may cause different failure phenomena, and the same failure may correspond to many different causes. For example, oil contamination may cause failures in hydraulic system pressure, flow or direction, etc., which brings great difficulty to hydraulic system fault diagnosis.

The idea of ​​​​diagnosing faults by the parameter measurement method is as follows. When any hydraulic system works normally, the system parameters work near the design and set values. If these parameters deviate from the predetermined values ​​during work, the system will fail or may appear. Fault. That is to say, the essence of the failure of the hydraulic system is the abnormal change in the working parameters of the system. Therefore, when the hydraulic system fails, it must be that a certain component or some components in the system are faulty, and it can be further concluded that the parameters of a certain point or a certain point in the circuit have deviated from the predetermined value. This shows that if the working parameters of a certain point in the hydraulic circuit are abnormal, the system has failed or may have failed, and maintenance person needs to deal with it immediately. In this way, based on parameter measurement, combined with the logic analysis method, the fault can be quickly and accurately found. Parameter measurement methods can not only diagnose system failures, but also predict possible failures, and both prediction and diagnosis are quantitative, which greatly improves the speed and accuracy of diagnosis. This kind of detection is a direct measurement, the detection speed is fast, the error is small, the detection equipment is simple, and it is easy to be popularized and used on the production site. Suitable for testing any hydraulic system. During measurement, it does not need to shut down or damage the hydraulic system, and can test almost any part of the system, not only can diagnose existing faults, but also conduct online monitoring and predict potential faults.

The principle of parametric measurement

As long as the working parameters at any required point in the hydraulic system circuit are measured and compared with the normal values ​​of the system, it can be judged whether the working parameters of the system are normal, whether there is a fault and the location of the fault.

The working parameters in the hydraulic system, such as pressure, flow rate, temperature, etc., are all non-electrical physical quantities. When using general instruments to measure by indirect measurement, these non-electrical quantities must first be converted into electrical quantities by physical effects, and then amplified, converted, and displayed. After processing, the measured parameter can be represented and displayed by the converted electrical signal. From this, it can be judged whether the hydraulic system is faulty. However, this indirect measurement method requires various sensors, the detection device is complex, and the measurement result has large errors and is not intuitive, which is not convenient for on-site promotion and use.

Parameter measurement method

Step 1: To measure the pressure, firstly tighten the hose connector of the detection circuit to the tee-threaded interface of the double ball valve. Open ball valve 2, close relief valve 3, and cut off the oil return passage. At this time, the pressure value of the measured point can be directly read from the pressure gauge (the actual working pressure of the system).

Step 2: Measure the flow and temperature - slowly loosen the handle of the relief valve 7, and then close the ball valve 1. Readjust the relief valve 7 so that the reading of the pressure gauge 4 is the measured pressure value, and the reading of the flow meter 5 is the actual flow value of the measured point. At the same time, the oil temperature value can be displayed on the thermometer 6.

Step 3: Measure the speed (speed) - whether the pump, motor, or cylinder, its speed or speed depends only on two factors, namely the flow rate and its geometric size (displacement or area), so as long as the motor or cylinder is measured The output flow (input flow for the pump) is divided by its displacement or area to get the speed or speed value.

example of parameter measurement

During the debugging of this system, the following phenomena occur: the hydraulic pump can work, but the pressure of the high-pressure pump supplying the clamping cylinder and the injection cylinder cannot rise (the pressure is adjusted to about 8.0Mpa, and it cannot be increased again), the pump has a slight abnormal mechanical noise, The water cooling system works, the oil temperature and oil level are normal, and there is oil return.

There are the following possible reasons for analyzing the failure from the loop:

(1) The overflow valve is faulty. Possible causes: incorrect adjustment, spring yield, orifice blocked, spool valve stuck.

(2) The electro-hydraulic reversing valve or electro-hydraulic proportional valve is faulty. Possible reasons: The return spring is broken, the control pressure is not enough, the spool valve is stuck, and the proportional valve control part is faulty.

(3) The hydraulic pump is faulty. Possible reasons: The pump speed is too low, the vane pump stator is abnormally worn, the seal is damaged, a large amount of air enters the pump suction port, and the filter is seriously blocked.

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