Spool Valve Research Articles

Reliability analysis for degradation process with abrupt jumps caused by operation state transition

This paper proposes a novel type of degradation process incorporating continuous degradation and abrupt degradation jump under dynamic operation states. By analyzing the failure mechanism of practical application, the abrupt degradation jump is comprehensively considered, and it is triggered by some certain state switching processes. Then, the reliability solutions of the degradation process (reliability function and moments of lifetime) are derived in the form of Laplace-Stieltjes transform. To a further step, inspired by the advanced equipment with long service span, the reliability solutions in limit region are explored, where an effective calculation method regarding statistical characteristics of degradation amount during regeneration epoch is pioneeringly proposed. To verify the proposed solutions in the form of Laplace-Stieltjes transform and their limit case, the representative example, spool valve, is implemented, and the results show the effectiveness and the feasibility of the solutions.

Unbalanced force analysis on valve core clamping in hydraulic spool valves

Hydraulic systems are widely used in nuclear power plant equipments. The reliability and stability of hydraulic systems can be seriously impacted by the valve core clamping resulting from unbalanced forces. This paper investigates the unbalanced force characteristics of hydraulic spool valve cores to identify the mechanisms behind such failures. Numerical models are established for hydraulic spool valve cores using sliding mesh technology with varying control face structures and space angles between the inlet and outlet, which are validated by experiments. The turbulent flow is modeled using the RNG k-ε model. Simulation results reveal that larger openings weaken the unbalanced force distribution while the larger inlet flow rates exacerbate the unbalanced force distribution, and control face structures significantly impact force distribution by altering the throttling effect of the throttle orifice. Furthermore, the impact of the space angles between the inlet and outlet is little compared with other parameters. These findings provide a reference for designing and optimizing hydraulic spool valves, contributing to higher reliability and stability of hydraulic systems.

Transient Flow Characteristics of a Pressure Differential Valve with Different Valve Spool Damping Orifice Structures

Lubrication system failure is a significant cause of in-flight shutdown incidents in aviation engines. The pressure differential valve, an essential component of a certain type of aviation engine lubrication system, is responsible for controlling the flow rate and pressure of the lubricating oil. Comprehending the transient flow characteristics of the pressure differential valve is of paramount importance for the secure operation of lubrication systems. This paper establishes a transient flow model of a pressure differential valve based on a transient computational fluid dynamics (CFD) method, and the experimental validation demonstrates the effectiveness of the computational model. The internal flow characteristics of the differential pressure valve at different stages during the opening process were studied. Additionally, four transient lubricating oil flow models with different valve spool damping orifice were established to analyse the impact of damping orifice structure on valve spool movement characteristics, pressure control characteristics, and flow field distribution. The results indicate that when the diameter of the valve spool damping orifice increases from 0.3 mm to 1.0 mm, the valve spool displacement and fluid force increase by 88 % and 20 %, respectively. Meanwhile, the peak valve spool velocity, peak oil supply pressure, and steady-state value decreased by 15 %, 29 %, and 34 %, respectively. As the length of the valve spool damping orifice increases from 0.894 mm to 4.0 mm, the growth rate of valve spool displacement and fluid force gradually decreases, with the peak valve spool velocity decreasing by 7 %. This study has potential significance for the structural optimization and application of pressure differential valve in lubrication systems.

Analysis of Underlapped Symmetrically Ported Valve-Controlled Asymmetric Cylinder Drive

The valve-controlled cylinder drive system is the most common type among hydraulic applications. Nonlinear behaviour in such systems is inevitable when the valve spool is around its null position. We utilised the component linking method to investigate the nonlinearities in a Moog valve-controlled asymmetric cylinder drive system by simulation in Fortran, in which a generalised concept is introduced and validated by comparing to the experimental results. An X factor is proposed in the generalised concept to describe the asymmetric cylinder state, which is a constant when the cylinder is extending or retracting, but numerically calculated when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method. This paper utilises the component linking method to simulate the Moog valve-controlled asymmetric cylinder drive system in Matlab Simulink, and proposes an analytical solution for the X factor when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method.

Design and optimization of hydraulic slide valve spool structure based on steady state flow force

This article studies the structure of hydraulic spool valve and the influence of different pressure differences on steady-state flow force. An improved scheme of designing a jet guide groove on the valve core is proposed to compensate for steady-state flow force. This article uses the CFD method to study the influence of spool valve structural parameters on steady-state flow force. The response surface method is used to establish the Polynomial regression model of the steady-state flow force, and the optimal structure size of the jet guide slot is obtained. The results indicate that the flow force increases with the increase of pressure difference. Moreover, under the same operating conditions, the absolute flow force of the spool valve with jet guide groove is smaller than that of the spool valve without jet guide groove. Therefore, the jet guide groove can effectively compensate for steady-state flow force, improve the control accuracy of the valve, and improve the stability of the spool valve.

Modeling and simulation analysis of a novel proportional water flow valve with a digital pilot stage

The position straightness of the hydraulic supports is the key factor to the intelligent fully mechanized mining, and the adjacent cylinder is the actuator used to pull the hydraulic support. However, the control component of the adjacent cylinder is electromagnetic on/off valve that cannot control the movement of adjacent cylinder proportionally. Therefore, a novel proportional water flow valve with a digital pilot stage is proposed to control the trajectory of adjacent cylinder precisely. The novel valve consists of a dual active cartridge main valve and a digital pilot valve that includes a high speed on/off valve A (HSV-A) and a throttle valve piloted by the high speed on/off valve B (HV-B). A coupling dynamic mathematical model of the flow valve is formulated and the dynamic characteristics of the valve is analyzed theoretically. The fluctuation of the throttle valve and main spool motion is also analytically calculated. In addition, the influences of the control parameters and key structural parameters on the throttle valve and the main valve's motion are analyzed on the basis of AMESim simulation respectively. The simulation results have demonstrated that the displacement fluctuation of the valve can be reduced by increasing the control frequency. The throttle valve closed-loop displacement fluctuation is about 0.2 mm and 0.1 mm when the control frequency is 100 Hz and 200 Hz. What's more, decreasing the main valve orifice diameter can also effectively lower the main valve displacement fluctuation, while it will diminish the main valve response speed at the same time.

Study of a proportional spool valve noise by means of Functional Data Analysis: Cavitation and intensity detection

Cavitation inside hydraulic components is a well-known issue, that arises under specific operating conditions. When this phenomenon occurs in valves, it leads to several issues, such as materials damage, performance reduction, and noise. The latter of them is becoming increasingly important in the transport sector, which is moving towards new technologies (i.e., electrification) that are notoriously quiet. Therefore, cavitation detection is becoming a matter of interest for several applications. The purpose of the work presented is to develop a diagnostic technique to detect the onset of cavitation in proportional valves. A 2-way 2-position proportional spool valve has been placed inside an acoustic enclosure; noise signals have been recorded by means of a high frequency microphone, for different flow rates and valve openings. Sound pressure levels have been analysed by means of statistical techniques; a Functional Data Analysis (FDA) has been performed in the open-source R environment, in which the experimental data, collected under different non-cavitation conditions, have been firstly used to perform a Functional Principal Component Analysis (FPCA) and then to define a threshold. Then, a further experimental dataset has been evaluated through a Hotelling control chart, from which it is possible to distinguish cavitating conditions as they fall outside the limits.

A prediction model of fluid–solid erosion wear in hydraulic spool valve orifice

Fluid–solid erosion wear may damage the port structure and change the linear characteristics of the spool valve. They may also affect null characteristics and the control accuracy of the valve, resulting in production and safety accidents. In the present study, the prediction model of the orifice throttling coefficient and worn profile for engineering applications such as compensation control and life degradation assessment is established. The collision probability between particles and the wall surface is particularly considered based on the E/CRC erosion wear model. The relationship between the spool opening and the impact angle of particles is investigated numerically when developing collision probability model. Meanwhile, the influence of particle concentration, spool opening, and differential pressure on the orifice throttling coefficient and worn profile is analyzed by experiments, and the microcosmic surface morphology of the spool metering edge is analyzed by scanning electron microscopy (SEM). The results show that the impacting of solid particles on the orifice will result in extrusion-thin platelets flaking wear and deformation wear. The maximum relative error between the predicted results and the experimental measurements is 2.25%. Moreover, the predicted results of the model are in good agreement with the measured values under different particle concentrations, spool openings and differential pressure.

Experimental and Numerical Analysis of Flow Force Acting on the Spool of Proportional Directional Valve

This paper deals with the experimental and numerical analysis of the flow force acting on the spool of a proportional directional valve. The flow force arises due to the fluid flow through the flow path of the proportional directional valve and significantly influences the dynamics of the valve spool. The valve under investigation is a three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The dependence of the valve spool flow force on the volumetric flow rate is measured as part of the experiment. The measurements are performed for different spool displacements. The measured data will be used to verify the numerical simulations. The proportional directional valve was modified so that a force sensor could be included on the spool axis to realize the experiment. Firstly, the flow force is measured as the fluid passes through the two flow paths of the valve (PB and AT). Subsequently, the experimental setup is modified to determine the flow force when the fluid passes through each flow path separately. The measurements are compared. Simulations of the flow through the proportional directional valve are performed using Ansys Fluent 2022 R2 software to determine the flow forces acting on the valve spool. Simulations are performed for the selected spool positions of the proportional directional valve. Finally, the results of the simulation and the experiment are compared. The contribution of this study is a CFD model of the flow paths of the proportional directional valve verified by experiment. The CFD model will allow the flow force analysis for different flow path geometries of the investigated valve. Experimental analysis of flow force is performed over the entire spool stroke at different volumetric flow rates. The flow forces are measured for each flow path separately and for both flow paths simultaneously.

Експериментальні дослідження електросуперфінішного оброблення сфокусованим струмом високоточних деталей авіаційного виробництва

The object of this study is the electrochemical superfinishing of high-precision aerospace assembly components (aircraft parts) by focusing on the current. The goal is to reduce the surface and edge roughness of high-precision parts of the spool valve type in a short time (up to 10-11 minutes) by implementing the principles of superfinishing along with electrochemical processes. The task: to conduct an experiment on the simultaneous processing of all the surfaces, edges, and grooves of a test sample of a high-precision part of a spool valve type by the electrochemical superfinishing method with a focused current. Methods of research include empirical analysis of existing and widespread methods of superfinishing, full-scale experiments, and inspection. The following results were obtained. According to the analysis, it was found that there are two the most widespread operations: electrochemical processing with subsequent superfinishing of the turbine working blades and processing of holes of various shapes and sizes. It was also found that the large number of superfinishing process parameters complicates its use for complex processing of aerospace assembly components. The authors proposed an alternative method – electrochemical superfinishing, the peculiarity of which is the use of a focused current that acts directly along the part generatrix, while the part rotates at high speed around its longitudinal axis in an electrolyte. Full-scale experiments were carried out on the simultaneous processing of all surfaces, edges, and grooves of a high-precision part sample of the spool valve type by electrochemical superfinishing, and positive results were obtained: part surfaces and edges roughness was reduced. It was found that the roughness decreases more intensively during the first minute of processing, and a higher initial roughness reduces better than an initially smaller roughness. Conclusions. The scientific novelty of the obtained results is as follows: electrochemical superfinishing with a focused current has been approved on the samples of high-precision aerospace components of the spool valve type; rounding of edges, improved roughness, and removal of burrs were obtained. The proposed method of processing use is rational when there is a need for accuracy of the working surface diameters of 0.001 mm, and it can be the subject of further research.

The Preparation, Microstructure, and Wet Wear Properties of an Fe55-Based Welding Layer with the Co-Addition of 0.01 wt% CeO2 and 1.5 wt% SiC Particles Using the Plasma Beam Spraying Method

Severe erosion wear is found on valve spools, which threatens the safety and reliability of these units. The use of the plasma beam spraying surfacing method can significantly improve the corrosion resistance and sealing performance of hydraulic valve spools, reduce material waste, and reduce maintenance costs. The effects of the co-addition of CeO2 and SiC particles on the morphology, surface cracks, microstructure, precipitated phases, and wear property of plasma-beam-sprayed Fe55-based coatings on 1025 steel were investigated using OM, EDS, ultra-deep field microscopy, and a wet sand rubber wheel friction tester, respectively. The dendrite exhibited a directional growth pattern perpendicular to the substrate and the transitional states of the microstructure with the co-addition of CeO2 and SiC particles. CeO2 or SiC reduced the liquid phase diffusion coefficient DL of Cr and C and resulted in a decrease in the G/R ratio. The dendrites changed into equiaxed grains. The main phase composition of the Fe55 welding layer was Cr7C3, γ-Fe. The martensite in the surfacing layer and the carbides formed Cr7C3, which can improve the hardness of the surfacing layer. The grain boundaries consisted mainly of a reticular eutectic structure. The uniform distribution of the Cr7C3 hard phase in the Fe55+1.5 wt% SiC+0.01 wt% CeO2 resulted in a uniformly worn surface. The sub-wear mechanisms during the friction process were micro-ploughing and micro-cutting. The hardness and toughness of Fe55+1.5 wt% SiC+0.01 wt% CeO2 were well-matched, avoiding excessive micro-cutting and microplastic deformation. A low content of CeO2 could lead to the formation of equiaxed grain and effectively improve the uniformity of the microstructure. The wear-resistant layer of Fe55+1.5 wt% SiC+0.01 wt% CeO2 can effectively improve the service life and long-term sealing performance of the valve spools.

Integrated mission reliability modeling for multistate manufacturing systems considering heterogeneous feedstocks based on extended stochastic flow manufacturing network

Mission reliability is a crucial health indicator for systematically characterizing the operational state and degradation process of manufacturing systems. However, the impact of heterogeneous feedstocks (qualified feedstocks and unqualified feedstocks) on processing machine degradation and the reliability of buffers have not received much attention in the existing research on mission reliability modeling of manufacturing systems. Accordingly, this study proposes a novel integrated mission reliability modeling method for multistate manufacturing systems considering heterogeneous feedstocks. Specifically, based on the operational mechanism of a multistate manufacturing system considering heterogeneous feedstocks and the connotation of the integrated mission reliability of the manufacturing system, an extended stochastic flow manufacturing network (ESFMN) model is constructed to quantify the interaction among processing machines, inspection machines, buffers, and heterogeneous feedstocks. By analyzing the mixture degradation of the processing machine under the impact of heterogeneous feedstock, an integrated mission reliability model for a multistate manufacturing system considering heterogeneous feedstocks based on ESFMN is established. Finally, an industrial example of the valve spool manufacturing system is given to illustrate the effectiveness and superiority of the proposed method.

Identification of pressure pulsation spectrum in a hydraulic system with a vibrating proportional valve

In this paper, attention was focused on identifying the components of the amplitude-frequency spectrum of pressure pulsations in a hydraulic system in which an external low-frequency mechanical vibration was subjected to a proportional hydraulic directional control valve. It was observed that an operating machine or device equipped with hydraulic valves is a source of mechanical vibrations with a wide frequency spectrum. The influence of these vibrations on the pressure pulsation spectrum was analyzed, identifying the components resulting from the forcing of the directional control valve spool. In addition, it was noted that the pressure pulsation spectrum includes components resulting from the pulsation of the displacement pump output feeding the hydraulic system. A description of these spectrum components was also made and, using the solution superposition method, the components of the pressure pulsation spectrum over a wide frequency range were identified.

Generation mechanism of high-frequency oscillation in proportional valve with a high-speed on/off valves bridge as the pilot stage

A digital proportional valve has a main spool that operates with a high-speed on/off valves bridge as the pilot stage. However, this can cause the spool to undergo high-frequency oscillation during movement, leading to a slower valve response, lower control accuracy, and even control failure. Therefore, it is important to study the oscillation mechanism of the valve. To address this issue, we establish a detailed dynamic model of the digital proportional valve, and analyze the factors affecting the response performance of the proportional valve spool. A method of half-bridge control based on duty cycle is proposed to eliminate the oscillation. The influence regularity of each factor on the response performance of the valve is explored. It is proved that the control method of the high-speed on/off valves bridge and the Pulse-width modulation (PWM) signal-switching frequency of the high-speed on/off valves are the main reasons for the oscillation of the main spool. The proposed half-bridge control method based on duty cycle can eliminate the oscillation in a lower frequency range. In addition, the results show that the pilot oil pressure is an important contributor to the oscillation; the higher the pilot oil pressure, the easier the main spool oscillation occurs. However, the spool mass, oil temperature, and coil temperature of the high-speed on/off valve do not affect the stability of the digital proportional valve.

Throttling characteristics prediction methodology for combined grooves in directional spool valves under variable flow rates

There is a contradiction between the calculation accuracy and cost when computing the pressure and flow rate. A throttling characteristics prediction methodology for directional spool valve was proposed to balance the contradiction. The throttling characteristics were represented by the flow-number, defined as the product of the flow coefficient and the orifice area, to reveal simultaneously the mapping relationships of the two versus the spool geometry, stroke and flow rate. The pressure and flow rate characteristics at different strokes were obtained through the computational fluid dynamic (CFD) simulations that were validated through bench testing. The concept of saturated flow-number theory was introduced to describe the effects of the flow rate on the flow-number. Models for the saturated flow-number and critical flow rate were established using the U-shape groove, a typical throttling structure, as an example to illustrate the effects of groove structure and opening. The throttling characteristics of the directional spool valve could be predicted by the flow-numbers of the combined grooves. The simulated and experimental results demonstrate that the prediction methodology achieves high calculation accuracy while incurring minimal costs. This methodology holds significant implications for the forward design of valve spool throttling structures.

Study on Optimal Design of Constant Current Water Distributor

Daqing Field has entered the late stage of ultra-high water cut development. The number of subzones of water injection wells is increasing year by year, and the number of zones of high-efficiency annual survey has exceeded 240,000. The testing capacity has reached a bottleneck, the contradiction among test efficiency, test team and qualified rate of water injection is becoming more and more obvious. The constant flow water distributor can keep the water injection quantity of the applied layer basically unchanged under the frequent fluctuation of water injection pressure, the water injection zone will be changed from repeated adjustment to little adjustment or even no adjustment, greatly reducing the testing workload and improving the testing efficiency. In order to further improve the performance of constant-current water distributor, the stress simulation of valve spool of constant-current water distributor was carried out. Based on the mechanical analysis of the valve core of constant flow distributor, the force acting on the valve core of constant flow distributor is obtained by numerical simulation, and the accuracy of the simulation results is verified by laboratory experiments. According to the requirements of starting pressure difference and spring stiffness of constant current water distributor, the constant current water distributor is optimized and perfected. The experimental results show that the error is less than 5%, which meets the requirements of field application. This study provides a basis for further improving the design of constant-current water distributor. Up to now, 392 wells have been tested with constant-current distributor, the effect of constant-current is good, and the average efficiency of single well is increased by 28.3%.

Cybernetic Proportional System for a Hydraulic Cylinder Drive Using Proportional Seat-Type Valves

Hydraulic cylinders are well known as cheap and robust actuators for moving heavy loads, especially in harsh environments. For this reason, they are often used in construction machines such as excavators. Basically, the hydraulic cylinders are controlled by four-way proportional spool valves, resulting in poor energy efficiency due to resistance control. Furthermore, because all valve edges are located at the same spool, common proportional valves suffer from limited flexibility with regard to different loads. Independent metering (IM) is a well-known strategy for making proportional hydraulic drives more efficient and more flexible because each port of the actuator can be connected individually to pressure or tank by independent two-way proportional valves. In this paper, the IM concept is realized as an open-loop control for a hydraulic cylinder drive, which, in combination with a human operator, constitutes a so-called cybernetic proportional system (CPS). The piston velocity commanded by the operator is controlled by the compensation of the static characteristics of the proportional seat-type valves. Basic simulations show the benefits and also the problems of open-loop independent metering. Furthermore, measurements on one actuator of a real excavator regarding controllability and energy consumption are presented.

Simulation and experimental research on steady flow force compensation for a servo proportional valve

In the development of high-performance directly driven proportional directional valves, reducing the flow force of the spool is a crucial aspect due to its significant influence on the dynamic characteristics and power consumption of these valves. This paper presents a study on the steady-state flow force of a servo-proportional valve spool by employing a combined approach of numerical simulations and experiments. Additionally, a method is proposed to compensate for the steady-state flow force by modifying the shoulder inclination of the spool. The results demonstrate that modifying the shoulder angle of the spool alters the emergence angle, leading to a substantial reduction in the steady-state flow force acting on the spool. Notably, the compensation method has negligible impact on the through-flow capability of the servo-proportional valve.

Fault diagnosis of power-shift system in continuously variable transmission tractors based on improved echo state network

For better reliability of tractors with continuously variable transmission, reported here is fault diagnosis of their power-shift systems. First, four hydraulic system faults are analyzed, i.e., pipe leakage, pipe blockage, a stuck solenoid valve spool, and a stuck clutch piston, and it is shown that these lead to clutch energy loss during power shifting and possibly even clutch burn-out. Second, fault simulations give more than 30000 groups of test data, and an improved dynamic time warping algorithm is used to segment the data samples automatically. Third, an improved echo state network is proposed to classify the above fault samples, and its performance is compared with those of traditional algorithms. Finally, the robustness of the proposed algorithm is tested using samples with noise superimposed. The results show that the accuracy, precision, recall, and F1-score of the improved echo state network are 96.87%, 96.31%, 97.11%, and 96.71%, respectively, making it equivalent in performance to a convolutional neural network with long short-term memory. However, the training speed of the former is significantly better than that of the latter, and even under the influence of strong noise, the proposed algorithm can still achieve an accuracy of 91.32%, which is better than the latter’s 86.62%. This is significantly better than traditional algorithms, thus demonstrating the better generalization characteristics and robustness of the proposed approach.

Review of Recent Advances in the Drive Method of Hydraulic Control Valve

Hydraulic control valves are widely used in industrial production, agricultural equipment, construction machinery, and other large power equipment for controlling the pressure and flow of fluids in hydraulic systems. The driving method has a significant impact on the response and control accuracy of hydraulic valves. This paper reviews the driving methods of spools from five aspects: solenoid drive, material expansion drive, motor drive, hydraulic valve drive, and another drive. It summarizes the various schemes currently available for spool drive and analyzes each of them. After optimizing the driving method of the valve core, the control accuracy can reach 3%, and the minimum response time is 7 ms. According to the characteristics of the different drive methods, the differences between them are compared, the advantages and disadvantages of each drive method are analyzed, and the application scenarios for each drive method are identified. Solutions to the drawbacks of the existing drive methods are proposed, which provide directions for further optimization. We have found that solenoid drives are simple to control, low cost, and the most widely used. Material telescopic drives, motor drives, hydraulic valve drives, and other drives are costly, complex to control, and optional for use in special requirement situations. Based on the existing spool drive methods, an outlook on future drive methods is presented. This review facilitates a comprehensive understanding of the drive methods of hydraulic valve spools, points out the shortcomings of the existing drive methods, and is of great significance in improving the existing drive methods and proposing new drive methods. This paper has a positive effect on improving the control accuracy and responsiveness of hydraulic valves.