Reliability Of Hydraulic System Research Articles

Evidence‐based fault tree analysis of the hydraulic system in CNC machine tools

AbstractThe hydraulic system is an integral part of CNC machine tools. In analyzing the reliability of machine tool hydraulic systems, their failures are influenced by both aleatory and epistemic uncertainties. This paper utilizes the fault tree analysis method to address failure modes subject to epistemic uncertainty, using the interval rough number scoring method to evaluate the probability of such failures occurring. The resulting reliability calculation is termed as “subjective reliability”. For failure modes influenced by aleatory uncertainty, objective data combined with the Dempster–Shafer evidence theory is used to determine their failure probability, with the corresponding reliability calculation referred to as “objective reliability”. Finally, a comprehensive calculation of both subjective and objective reliability is conducted to determine the overall reliability of the hydraulic system, along with the ranking of the importance of basic events of fault tree. This methodology covers scenarios with small samples, sufficient data, and their combinations, offering extensive application prospects.

Numerical Investigation of Micrometer-Sensitive Particle Intrusion in Hydraulic Valve Clearances and Its Impact on Valve Performance

The intrusion of micrometer-sensitive contaminant particles into the clearance of sliding valves within hydraulic fluids is one of the root causes of valve sticking and reliability issues in hydraulic systems. To reveal the transient process and characteristics of particle intrusion into the clearance process, this paper proposes a numerical method for fluid–particle one-way coupling and verifies it through experimentation. Furthermore, a numerical simulation of the motion trajectory of spherical iron particles inside the valve chamber was conducted in a two-dimensional flow model. It was discovered that in a steady-state flow field with a certain valve opening, micrometer-sized particles in the valve chamber’s hydraulic fluid mainly move with the valve flow stream, and the number of micron particles invading the slide valve clearance and the probability of invasion is related to the slide valve opening and differential pressure. When the slide valve opening decreases, especially in the small opening state, the probability of particles invading the slide valve clearance will increase dramatically, and the probability of invading the clearance is as high as 27% in a valve opening of 50 μm; the larger the pressure difference between the valve ports, the more the number of particles invading the slide valve clearance increases; the particles in the inlet of the slide valve clearance are more prone to invade the slide valve clearance, and invade in an inclined way, touching the wall and then bouncing back. These findings are of great value for the design of highly reliable hydraulic control valves and the understanding of the mechanism of slide valve stalls and provide an important scientific basis for the optimization and improvement in the reliability of hydraulic systems.

Improving the reliability of hydraulic systems for construction machinery using remote diagnosis

Improving the reliability of hydraulic systems for construction machinery using remote diagnosis

Macro and Micro Characteristics of Glyd-ring Seals in a Wide Temperature Range

Reciprocating seals are key components that affect the safety and reliability of hydraulic systems. This paper establishes a thermo-elastohydrodynamic (TEHD) model of Glyd-ring combined seals and reveals the macro and micro characteristics in a wide temperature range. Specifically, the TEHD model considers the changes in material and hydraulic oil parameters with temperature, and the parameter values at different temperatures are obtained through actual measurements. During the iterative calculation process of the TEHD model, parameters such as seal size, material, and hydraulic oil are constantly updated according to temperature changes. This paper also proposes a method to optimize the sealing performance of Glyd-ring seals by reducing the root mean square roughness.

Improving the reliability of hydraulic systems for construction machinery using remote diagnosis

The article considers the issue of improving the reliability of the hydraulic system of construction machines based on remote diagnostics. This allows you to optimize the operation of the structural elements of the hydraulic system, increasing the reliability of construction machines during operation. Real-time monitoring of the technical condition of key structural elements of construction machines helps to prevent failures, unforeseen costs, increase the resource and the level of safety of construction machines. Keywords: reliability, construction machine, hydraulic system, remote diagnostics

Improving the reliability of hydraulic systems of technological machines

Modern technological machines have in their design hydraulic systems that are used to control the working body of the machine. Currently, hydraulic systems are complex systems that consist of a large number of subsystems and separately functioning elements. An analysis of the reasons leading to the failure of hydraulic systems shows that their reliability depends on a large number of factors, which are often interconnected. These factors include the external influence of the environment, the properties of materials and working hydraulic fluid, wear processes, the magnitude of the loads, the operating time, as well as regulations for the maintenance of the hydraulic system as a whole and its individual elements. As the statistics of hydraulic systems failure show, about sixty percent of failures are associated with contamination of the working fluid. It is possible to prevent contamination of the hydraulic system at the design stage or by changing the organization of maintenance. It is shown that the number of sensors registering the level of contamination of the hydraulic fluid and their placement on the machine body must be scientifically substantiated. The studies presented in the article allow us to make a conclusion about the possible formation of stagnant zones in remote nodes of the hydraulic system. An important result of this research is that dynamic data collected by the built-in particle detection sensors can give inaccurate information about the condition of the hydraulic fluid. Evaluation of modern methods of technical operation has made it possible to identify a priority condition that will allow the transition from diagnostic to predictive assessment of the state of elements of hydraulic systems of technological machines.

A multi-scale finite element contact model for seal and assembly of twin ferrule pipeline fittings

Abstract As the seal and connection piece of pipeline, assembly method and the seal characteristics of pipeline fittings are important for the safety and reliability of hydraulic system of aircraft. According to measured data of roughness of the target surfaces, a multi-scale model for considering the rough surfaces is established and the assembly process of the pipeline fittings is simulated. In the process of simulation, the seal status and seal characteristics of fittings, as well as the influence of fluid pressure on the seal performance are studied in detail. The results show that the change in stress distribution extends around two high stress regions, and multi-scale model could really reflect seal characteristics during the assembly process of pipeline fittings. Moreover, the variation of contact area between front ferrule and pipeline can be described in the linear relations of three stages, and with the increase of fluid pressure, the rate of change of contact area will also increase.

Modeling of Cavitation-Induced Air Release Phenomena in Micro-Orifice Flows

Impurities like air bubbles in hydraulic liquids can significantly affect the performance and reliability of hydraulic systems. The aim of this study was to develop a model suited for hydraulic system simulation to determine the rate of degassing of dissolved air in a micro-orifice flow at cavitating conditions. An existing model for the flow through a micro-orifice was extended to account for the generation of vapor which is suggested to play the key-role for the degassing mechanism. In comparison with measurements, the results of the modeling approach imply that diffusive mass transfer of dissolved air into generated vapor cavities is the dominating mechanism for the observed air release phenomena.

Hydraulic Impulse-Testing System with Pressure Difference Feedback from a Second-Stage Valve

AbstractTo guarantee the reliability of hydraulic systems, it is of vital importance to do impulse testing for hydraulic components. A hydraulic impulse-testing system with pressure difference feedback from a second-stage valve is studied. A mathematical model of the system is built, and it shows that the inner closed-loop damping ratio of the system is influenced by the pressure difference feedback of the control chambers of the second-stage valve. And by changing the pressure difference feedback gain, various damping ratios can be achieved, which is a key factor affecting the system overshoot. The results of both the simulation and experiment show that with the same square wave input the system overshoot can be freely controlled between 0 and 50% by adjusting the pressure difference feedback gain, which is a new method to obtain both peak wave impulse pressure cycle and square wave impulse pressure cycle utilizing the same system and the same input.

A Hybrid Fault Diagnosis Approach for Hydraulic Systems by using Radial basis Function Networks

To improve the reliability of hydraulic systems, a fault diagnosis approach based on radial basis function (RBF) networks was proposed in this paper. According to the target fault features extracted from a fuzzy auto-regressive with extra outputs (FARX) model, RBF networks serve as a fault classifier and the output of the RBF networks is the result of fault diagnosis. Several typical faults of hydraulic systems were used to test the fault diagnosis approach. Experiment results showed that the fault diagnosis approach is feasible and effective for improving the reliability of hydraulic systems.

Analysis and Control of the Fault in the Hydraulic System of Coal-Machinery

This paper focused on the analysis of the invaders brought into the hydraulic system in the design, manufacture, installation, working and maintenance of the process and the fault caused by the invaders to the hydraulic system of coal machine . The method of reducing the invader in oil of hydraulic system and tincreasing the reliability of hydraulic system was indicated.

Hydraulic System Reliability Analysis of Slurry Transportation Based on Stochastic Failure Petri Net

As the development of the slurry pipeline transportation system complexity and intelligent,it is more difficult to establish the reliability of the system.This pape take advantage of the descriptions of dynamic systems of stochastic failure petri net,applying in the field of slurry pipeline transport system reliability analysis.At same time,with the combination of Markov theory, it established the model of the hydraulic system reliability analysis.The feasibility and availability of the method is proved through an example of hydraulic system of slurry pipeline transportation.

Research into Cleaning and Suppression Equipment to Improve Reliability of Hydraulic System

Modern weapons are usually power-driven by hydraulic system, The reliability of hydraulic systems restricts the reliability of weapons. The research elaborated in this paper is focused on cleaning and suppression equipment, with the aim of implementing a thorough cleaning and maintaining of hydraulic system pipes and checking the pressure. Pipe cleaning and suppression is an essential step to guarantee the reliability of hydraulic system and the service life of hydraulic parts, thus improving the reliability of weapons.

Reliability-based maintenance scheduling of hydraulic system of rotary drilling machines

Hydraulic system has a critical and important role in drilling machines. Any failure in this system leads to problems in power system and machine operation. Since the failure cannot be prevented entirely, it is important to minimize its probability. Reliability is one of the most efficient and important method to study safe operation probability of hydraulic systems. In this research, the reliability of hydraulic system of four rotary drilling machines in Sarcheshmeh Copper Mine in Iran has been analyzed. The data analysis shows that the time between failures (TBF) of Machines A and C obey the Weibull (2P) and Weibull (3P) distribution, respectively. Also, the TBF of Machines B and D obey the lognormal distribution. With regard to reliability plots of hydraulic systems, preventive reliability-based maintenance time intervals for 80% reliability levels for machines in this system are 10h.

Reliability Prediction Method of Hydraulic System by Fuzzy Theory

The hydraulic system's reliability is a key factor to ensure the reliable operation of equipment and it is very important to evaluate reliability of hydraulic system. The paper describes a reliability prediction method that may be used to evaluate the reliability of hydraulic systems for industrial applications. The proposed method takes advantage of fuzzy set theory. The aim of this method is to minimize the deficiencies of the traditional reliability prediction methods treating a failure rate as fixed value due to insufficiency practice data. Triangular fuzzy number and Gaussian fuzzy number are used in the application of this prediction method, where environmental factor, derating factor, and other factors are considered. Finally, an example of type crane's hydraulic system is given to verify the feasibility and practicability of the method.

The Roadheader Rear Support System Modeling and Mechanical-Hydraulic Coupling System Co-Simulation Research

In order to estimate the stability of the roadheader rear support system, took the heavy cantilever roadheader of a coal company as the research object, rigid-flex coupled dynamic model of its rear support system was established based on Pro/E, ADAMS and ANSYS. The hydraulic control system model of rear support was researched in EASY5. These two models built the mechanical-hydraulic coupling system. Analysed the mechanical dynamic simulation results and verified the reliability of hydraulic system when the co-simulation of rear support was made.

Reliability Analysis Using GO Methodology and Grey System Theory

Machining center is a complex mechatronical product. Because of numerous influencing factors on its reliability, parts of their inaccurate description and the uncertainty of its failure behaviors, it is very difficult to analyze its reliability by traditional reliability model which is based on probability theory. To solve this problem, grey system theory combined with GO method reliability analysis was presented, and sequentially a practical reliability analysis model considering various operating conditions of the components of machining center was established. The method was used in reliability analysis of hydraulic system of Tray Automatic Exchange Device (TAED) of machining center. Firstly, through a systematical analysis of hydraulic system of tray automatic exchange device of machining center, its basic structure model was summarized, and the model of GO chart for the hydraulic system was established. Then, the gray dynamic analysis for the hydraulic system was derived, and a feasible method of dynamic analysis for the performance reliability of hydraulic system was provided. Finally, the availability and correctness of this method in the analysis and reliability evaluation of machining center was verified by comparing the calculated result of this method with that of the traditional static GO methodology and the FTA. This approach provided a theoretical basis for the prevention of failures of the hydraulic system of tray automatic exchange device, the improvement of the system reliability and security, and the development of security controls.

Monitoring of Cleanliness Level in Hydraulic Systems: Obtaining Reliable On-Line data

Monitoring of system cleanliness levels and counting of particulate contaminant are fundamental to achieving hydraulic system reliability as any departure from the specified cleanliness level is often a precursor to future failures. On-line monitoring of cleanliness levels has the advantage of giving data both very quickly and accurately as environmental influences are eliminated. In this way, corrective actions can be promptly implemented. Most on-line instruments are sensitive to system conditions to a greater or lesser extent, but Automatic Particle Counters (APCs) working on light extinction principles are especially sensitive to the presence of optical interfaces caused by such conditions as fluid mixtures, emulsions, free water and air bubbles. These conditions give erroneous data and can result in drawing incorrect conclusions, wasting maintenance time and ultimately, reduced user confidence in cleanliness monitoring. This paper describes such conditions and shows how the correct selection of the analysis technique can result in reliable cleanliness level data.

Adaptive wavelet transform for vibration signal modelling and application in fault diagnosis of water hydraulic motor

There has been an increasing application of water hydraulics in industries due to growing concern on the environmental, health and safety issues. The fault diagnosis of water hydraulic motor is important for improving water hydraulic system reliability and performance. In this paper, fault diagnosis of water hydraulic motor in water hydraulic system is investigated based on adaptive wavelet analysis. A novel method for modelling the vibration signal based on the adaptive wavelet transform (AWT) is proposed. The linear combination of wavelets is introduced as wavelet itself and adapted for the particular vibration signal, which goes beyond adapting parameters of a fixed-shape wavelet. The AWT procedure based on the parametric optimisation by genetic algorithm (GA) is developed. The model-based method by AWT is applied to extract the features in the fault diagnosis of the water hydraulic motor. This technique for de-noising the corrupted simulation signal shows that it can improve the signal-to-noise ratio of the vibration signal. The results of the experimental signal demonstrate the characteristic vibration signal details in fine resolution. The magnitude plots of the continuous wavelet transform (CWT) show the characteristic signal's energy in time and frequency domain which can be used as feature values for fault diagnosis of water hydraulic motor.

WAVELET–BASED PRESSURE ANALYSIS FOR HYDRAULIC PUMP HEALTH DIAGNOSIS

The diagnosis of hydraulic pump health in realtime is important for increasing hydraulic system reliability andperformance. Because of high noise levels in the pump pulsation pressure signal, many existing health diagnosis methods,such as limit checking, spectrum analysis, and logic reasoning, cannot effectively perform a reliable online health diagnosisfor hydraulic pumps. Wavelet analysis, a waveform signal analysis method performed by breaking up an evaluating signalinto shifted and scaled versions of a standard wavelet, can identify feature signals in multiple decomposed band windows ofthe original signal. The methodology for applying this wavelet analysis in realtime health diagnosis for hydraulic pumpswas investigated in this study. Results obtained from both simulation analysis and online experimental validation verifiedthat the wavelet analysis method can improve the capability of diagnosing the health conditions of piston pumps, and moreimportantly can identify the types of pump defects based on the patterns and the amplitudes of obtained wavelet coefficients.