Daily Methods for Diagnosing Faults in Custom Hydraulic Systems

Daily methods for diagnosing faults in custom hydraulic systems

The traditional method for diagnosing faults in custom hydraulic systems on a daily basis involves logical analysis and gradual approximation until the problem is identified.

The basic approach involves comprehensive analysis and conditional judgment. That is, the maintenance personnel, through observation, listening, touching, and simple tests, as well as their understanding of the hydraulic system, make judgments based on experience regarding the cause of the malfunction. When a hydraulic system fails, there are many possible causes for the failure. Using the logical algebra method, a list of possible causes of the failure is made, and then logical judgments are carried out in accordance with the principle of starting from the easier to the more difficult, step by step, to identify the cause of the failure and the specific conditions that led to it.

During the process of customizing the hydraulic system fault diagnosis, it is required that the maintenance personnel possess basic knowledge of the hydraulic system and strong analytical skills in order to ensure the efficiency and accuracy of the diagnosis. However, the diagnosis process is rather cumbersome, involving numerous inspections and verifications, and can only be conducted qualitatively. As a result, the diagnosed fault causes are not accurate enough. For

To reduce the blindness and subjectivity of system fault detection as well as the workload of disassembly and assembly, traditional fault diagnosis methods have been far unable to meet the requirements of modern hydraulic systems. With the development of hydraulic systems towards larger size, continuous production, and automatic control, various modern fault diagnosis methods have emerged. For instance, ferrographic analysis can determine the wear location, form, and degree of components in the system through the quantity, shape, size, composition, and distribution pattern of various abrasive particles separated from the oil. Moreover, it can conduct quantitative analysis and evaluation of the contamination of hydraulic oil, enabling online detection and fault prevention.

The expert diagnosis system based on artificial intelligence works by having the computer imitate the problem-solving methods of experienced experts in a certain field. The fault phenomena are input into the computer through the human-machine interface. Based on the input phenomena and the knowledge in the knowledge base, the computer can calculate the cause of the fault and then output this cause through the human-machine interface, and propose maintenance plans or preventive measures. These methods bring broad prospects for hydraulic system fault diagnosis and lay the foundation for the automation of hydraulic system fault diagnosis. However, these methods generally require expensive detection equipment and complex sensing control systems and computer processing systems. Some of these methods are somewhat difficult to study and are generally not suitable for on-site promotion and application. The following introduces a simple and practical method for hydraulic system fault diagnosis.

2. Fault Diagnosis System Based on Parameter Measurement

Whether a custom hydraulic system is functioning properly mainly depends on two key working parameters, namely whether the pressure and flow are in a normal working state, as well as the normality of parameters such as system temperature and actuator speed. The fault phenomena of hydraulic systems are diverse, and the causes of faults are the result of a combination of various factors. The same factor may cause different fault phenomena, while the same fault may correspond to multiple different causes. For example: contamination of the oil may cause faults in various aspects of the hydraulic system, such as pressure, flow, or direction, which brings great difficulties to the diagnosis of faults in custom hydraulic systems.

The idea behind using parameter measurement to diagnose faults is as follows: When any hydraulic system is operating normally, the system parameters are always close to the designed and set values. If these parameters deviate from the predetermined values during operation, the system will either malfunction or there is a possibility of a malfunction. In other words, the essence of a hydraulic system malfunction is the abnormal change in the system's operating parameters.

Therefore, when a custom hydraulic system malfunctions, it must be that a certain component or some components in the system are faulty. Further, it can be concluded that the parameters at a certain point or several points in the circuit have deviated from the predetermined values. This indicates that if the working parameters at a certain point in the hydraulic circuit are abnormal, then the system has malfunctioned or may have malfunctioned, and maintenance personnel need to handle it immediately. Based on parameter measurement, combined with logical analysis methods, the fault can be quickly and accurately located. The parameter measurement method not only diagnoses system faults, but also predicts possible faults, and this prediction and diagnosis are quantitative, greatly improving the speed and accuracy of diagnosis. This detection is direct measurement, with fast detection speed, small error, simple detection equipment, and is easy to be promoted and used in the production site. It is suitable for the detection of any hydraulic system. During measurement, there is no need to stop the machine, and the hydraulic system is not damaged. It can almost be used to detect any part of the system, not only diagnosing existing faults, but also conducting online monitoring and predicting potential faults.

Principle of Parameter Measurement Method

As long as the working parameters at any point in the hydraulic system circuit are measured, and compared with the normal values of the system operation, it is possible to determine whether the system's working parameters are normal, whether a fault has occurred, and where the fault lies.

The working parameters in the customized hydraulic system, such as pressure, flow rate, and temperature, are all non-electrical quantities. When measured using general instruments through indirect measurement methods, first, these non-electrical quantities need to be converted into electrical quantities by utilizing physical effects. Then, through amplification, conversion, and display processes, the measured parameters can be represented and displayed by the converted electrical signals. Thus, it is possible to determine whether there is a fault in the hydraulic system. However, this indirect measurement method requires various sensors and complex detection devices, resulting in large measurement errors, lack of intuitiveness, and inconvenience for on-site promotion and application.

Parameter measurement method

1: To measure pressure, first connect the hose connector of the detection circuit to the three-way threaded interface of the double ball valve. Open valve 2, close the relief valve 3, and cut off the return oil path. At this point, the pressure value at the measured point (the actual working pressure of the system) can be directly read from the pressure gauge.

2: Measure flow rate and temperature - Gently release the handle of the overflow valve 7, then close the ball valve 1. Re-adjust the overflow valve 7 so that the reading on the pressure gauge 4 is the measured pressure value. At this point, the reading on the flow meter 5 will be the actual flow rate at the measured point. At the same time, the temperature gauge 6 can display the temperature value of the oil.

3: Measuring rotational speed (velocity) - Regardless of whether it is a pump, a motor, or a cylinder, the rotational speed or velocity of these components depends only on two factors: the flow rate and its own geometric dimensions (displacement or area). Therefore, as long as the output flow rate (for a pump, it is the input flow rate) is measured for the motor or cylinder, divide it by its displacement or area to obtain the rotational speed or velocity value.

Example of Parameter Measurement Method

During the debugging process of this system, the following phenomena were observed: The pump can operate, but the pressure supplied to the mold closing cylinder and the injection cylinder cannot be increased (even when the pressure is adjusted to around 8.0 Mpa, it cannot be further increased). There is a slight abnormal mechanical noise from the pump. The water cooling system is working, and the oil temperature and oil level are normal, with oil return.

From the circuit analysis, the possible causes of the fault are as follows:

(1) Overflow valve malfunction. Possible causes: incorrect adjustment, spring failure, blockage of the damping hole, or jamming of the slide valve.

(2) Fault of the electro-hydraulic directional valve or electro-hydraulic proportional valve. Possible causes: The reset spring is broken, the control pressure is insufficient, the slide valve is stuck, or the control part of the proportional valve is faulty.

(3) Hydraulic pump failure. Possible causes: pump speed is too low, stator of the vane pump is abnormally worn, seals are damaged, a large amount of air enters the pump suction port, or the filter is severely clogged.

3. Summary

The parameter measurement method is a practical and novel fault diagnosis approach for hydraulic systems. It is combined with the logical analysis method, significantly enhancing the speed and accuracy of fault diagnosis. Firstly, this measurement is quantitative, which avoids the blindness and subjectivity of personal diagnosis and ensures the diagnostic results are realistic. Secondly, the fault diagnosis is fast. It can obtain the accurate parameters of the system within a few seconds to several tens of seconds, and then the maintenance personnel can simply analyze and judge to obtain the diagnosis result. Moreover, this method reduces the system assembly and disassembly workload by more than half compared to traditional fault diagnosis methods.

This fault diagnosis detection circuit has the following functions:

It can directly measure and visually display the flow rate, pressure and temperature of the liquid, and can also indirectly measure the rotational speed of pumps and motors.

(2) The overflow valve can be utilized to simulate the loading of the measured part in the system, making the pressure adjustment convenient and accurate. To ensure the accuracy of the measured flow rate, the test temperature difference (which should be less than ±3℃) can be directly observed from the temperature gauge.

(3) It is applicable to any hydraulic system, and certain system parameters can be detected without stopping the system.

(4) The structure is lightweight and simple, operates reliably, has low cost, and is easy to operate.

This detection circuit combines the loading device with a simple detection instrument, and can be made into a portable detector. It is capable of measuring quickly, conveniently and accurately, and is suitable for widespread application on-site. It lays the foundation for the automation of detection, forecasting and fault diagnosis.