Hydraulic fault diagnosis is to determine whether the operating state of the hydraulic system of mechanical equipment is normal or abnormal, whether a hydraulic fault has occurred, and when the hydraulic system fails, determine the fault location of the hydraulic equipment and the nature and cause of the fault.
The content of hydraulic fault diagnosis includes three aspects: monitoring, identification, and prediction of the hydraulic system of mechanical equipment. The accuracy of hydraulic fault diagnosis is achieved by all the information provided by the diagnosed object; that is, through all the information provided by the diagnosed object, the characteristic parameters that can be used to identify the operating state of the hydraulic equipment are obtained through analysis and processing, and finally, the correct conclusion is drawn.
Hydraulic fault diagnosis includes simple diagnosis means and precise diagnosis means. Simple diagnostic methods include sensing detection, system diagram analysis and detection, fault tree analysis, etc. Precise diagnostic methods include oil analysis, vibration acoustics, ultrasonic detection, computer-aided diagnosis, and so on. The following describes several common simple diagnosis methods.
1. Method of perception
The so-called wood sense test. That is, the maintenance personnel use the human body's senses to directly perceive the operating state of the hydraulic system, analyze and judge the location and cause of the fault, so as to determine the methods and measures to eliminate the fault. The main tools include:
(1) Touch - According to the sense of touch, to judge the level of the oil temperature (components and their pipes) and the size of the vibration.
(2) Vision - The use of vision to observe whether there is a lack of movement of the mechanism, movement instability, leakage, oil discoloration, pipeline damage, and loosening.
(3) Hearing through hearing, according to the abnormal sound of the hydraulic pump and hydraulic motor, the scream of the relief valve, and the vibration of the pipeline, to judge the size of the noise and vibration.
(4) Smell - Through the sense of smell, determine the deterioration of oil and hydraulic pump heating, sintering, and other faults. Maintenance personnel perceive the status of each part of the above hydraulic system through their senses, and then use experience to analyze whether there is a fault in the system and the fault location, and the cause. The method of perception is simple and practical, but the premise is that the user is very familiar with the structure and principle of the object system, and has rich practical experience
2. System diagram analysis and detection method
System diagram analysis and detection method, also known as the logical analysis method, which is, on the basic principle of the hydraulic system. By combining the hydraulic system diagram for logical analysis, reducing the suspect object, gradually approaching, and finding the fault location method.
The basic steps are as follows:
(1) Observe and analyze the abnormal operation of the hydraulic system, which can generally be summarized as three major problems: pressure, flow, and direction.
(2) Review the hydraulic system diagram and check the components, determine its performance and role, and preliminarily assess its quality status.
(3) Make a list of components related to the fault. It should be noted that it is necessary to exercise full judgment and not to miss any component that has an important impact on the fault.
(4) For the components listed in the list, line up according to the difficulty of their inspection, and list the key components and parts for inspection.
(5) The preliminary inspection should determine whether the selection and assembly of components are reasonable; Whether the component test method is correct; Whether the external signal of the component is appropriate, whether there is a response to the external signal; Pay attention to the precursors of component failure, such as high temperature, noise, vibration, and leakage.
(6) If the component causing the fault is not checked, the instrument is repeatedly checked until the component causing the fault is checked.
(7) Repair or replace the faulty component.
(8) Before restarting the equipment, carefully consider the antecedents and consequences of the failure, and predict the hidden dangers of possible failures to take appropriate technical measures.
3. Fault tree analysis
Fault tree analysis is an analysis method that gradually subdivides the causes of system failure from the whole to the part according to the tree shape, also known as the empirical logic method. The core problem of this method is to establish the fault tree of the object system. The so-called fault tree is a tree-like fault cause analysis diagram composed of the fault phenomenon as the top event, the fault cause as the bottom event, and other events between the two as intermediate events. After establishing a detailed and accurate fault tree, when a fault occurs. It can find the cause directly in the fault tree according to the fault phenomenon, so that the fault diagnosis of the hydraulic system becomes simpler and easier.
The so-called fault exhaustion method evolved from fault tree analysis, is often used in practice. The fault exhaustion method is to summarize and analyze the failure of a certain hydraulic system, and enumerate all possible fault phenomena and causes as far as possible. The exhaustive method is a powerful tool for beginners to diagnose and eliminate hydraulic system faults.
