Flapper-nozzle Valve Research Articles

Cavitation reduction of a flapper-nozzle pilot valve using continuous microjets

Abstract The flow cavitation in the flapper-nozzle stage is one of the main factors that produce the flapper vibration and thus deteriorate the performance of the flapper-nozzle servo valves. This work proposes a novel method, deploying two continuous microjets around the main jet of each nozzle, to suppress the cavitation. The cavitation reduction using continuous microjets is numerically examined in detail by comparing the vapor fraction with and without the microjets at different inlet pressure, housing diameter and the null clearance. The mass flow rate measurements and the flow visualization are conducted to validate the numerical simulation. It is found that the cavitation in the flapper-nozzle stage is significantly reduced under the effect of the continuous microjets. And the flow cavitation exhibits a great dependence on the inlet pressure, housing diameter and the null clearance. In the traditional flapper-nozzle structure, the cavitation is strongly enhanced at high inlet pressure, small housing diameter or large null clearance. Nevertheless, the cavitation in the flapper-nozzle structure with the microjets is still remarkably suppressed at the same condition. This indicates that the continuous microjets are highly effective in reducing the cavitation of the flapper-nozzle valve.

Suppression of Squeal Noise Excited by the Pressure Pulsation from the Flapper-Nozzle Valve inside a Hydraulic Energy System

Squeal noise often occurs in a two-stage electrohydraulic servo-valve, which is an unfavorable issue of modern hydraulic energy systems. The root causes of such noise from the servo-valve are still unclear. The objective of this paper is to explore the noise mechanism in a servo-valve excited by the pressure pulsations from the hydraulic energy system perspective. The suppressing capability of squeal noise energy is investigated by changing the pressure pulsation frequency and natural frequency of the flapper-armature assembly. The frequencies of the pressure pulsations are adjusted by setting different speeds of the hydraulic pump varying from 10,400–14,400 rpm, and two flapper-armature assemblies with different armature lengths are used in the tested hydraulic energy system. The first eight vibration mode shapes and natural frequencies of the flapper-armature assembly are obtained by numerical modal analysis using two different armature lengths. The characteristics of pressure pulsations at the pump outlet and in the chamber of the flapper-nozzle valve, armature vibration and noise are tested and compared with the natural frequencies of the flapper-armature assembly. The results reveal that the flapper-armature assembly vibrates and makes the noise with the same frequencies as the pressure pulsations inside the hydraulic energy system. Resonance appears when the frequency of the pressure pulsations coincides with the natural frequency of the flapper-armature assembly. Therefore, it can be concluded that the pressure pulsation energy from the power supply may excite the vibration of the flapper-armature assembly, which may consequently cause the squeal noise inside the servo-valve. It is verified by the numerical simulations and experiments that setting the pressure pulsation frequencies different from the natural frequencies of the flapper-armature assembly can suppress the resonance and squeal noise.

Design criterion involving comprehensive performance characteristics of nozzle–flapper valves

The traditional parameter design rule for the nozzle–flapper valves has always followed the maximum control pressure sensitivity criterion; however, this article queries the validity of this traditional parameter design theory for the comprehensive performance characteristics of a flapper–nozzle valve. Accordingly, a new parameter design rule, which involves symmetry, linearity and sensitivity of the control pressure, was constructed from a detailed and rigorous mathematical derivation that employs a non-dimensional analysis method. Then, an effect verification of the new criterion and a comparison between the pressure–flow curves and three key valve coefficients, which are dominated by the traditional rule and the new criterion, respectively, are performed. Finally, the comprehensive performance characteristics of the flapper–nozzle valve, such as the reliability, response, accuracy, sensitivity, efficiency, anti- disturbance and control pressure range, which are produced by the two parameter design rules, are compared. The results indicate that the performance of nozzle–flapper valve followed by the new parameter design criteria is superior to the performance directed by the traditional one with respect to various indexes, such as the reliability, response, accuracy and anti-disturbance. In addition, for the design of nozzle–flapper valves, the studies have also revealed that the optimal values of the structural parameter are dependent on the actual flapper motion ranges and the priority of the above-mentioned performance indexes. All these new findings can develop and supplement the existing design theory of nozzle–flapper valve and can also be beneficial to the design of double-nozzle–flapper electro-hydraulic servo valves.

Cavity shedding dynamics in a flapper–nozzle pilot stage of an electro-hydraulic servo-valve: Experiments and numerical study

The performance of an electro-hydraulic servo-valve is significantly influenced by the characteristics of the flow field in the flapper–nozzle pilot stage. Cavitation and pressure oscillations frequently occur in the flow field of flapper–nozzle pilot stage and these undesired flow-induced phenomena commonly lead to the appearance of high frequency noises and vibrations of the servo-valve. To obtain in-death understanding about these flow-induced phenomenon, numerical and experimental study of the unsteady cavitation phenomenon in a flapper–nozzle pilot valve is carried out. Large Eddy Simulation (LES) coupling with Schnerr and Sauer mass transfer cavitation model is utilized to simulate the unsteady cavitation shedding around the sharp edge of the flapper. The simulations are conducted using the commercial CFD code ANSYS/FLUENT 14. Meanwhile, the flow field is experimentally observed by using a high speed video camera. The recorded images of the transient cavitation patterns are verified with CFD simulation results. Then, the characteristics of pressure oscillations at the beginning and the end of the shedding path in the flow field are evaluated by CFD approach. The results show that the increment of inlet pressure intensifies cavitation in the flapper–nozzle pilot stage and induces the shedding phenomenon. And both the frequency and magnitude of pressure oscillations in the flapper–nozzle valve are enhanced by increasing the inlet pressure.

Pneumatic single flapper nozzle valve driven by piezoelectric tube

The article presents a construction, static testing and modelling of a single flapper nozzle pneumatic valve. Authors show testing of piezo tube PT230 which distinguishing feature is deflection in two directions. This testing is preliminary work in design of a novel electropneumatic valve. Studies have been performed on a special designed bench which consists of a pneumatic valve, which used piezo tube as a flapper. Data acquisition process and control were performed by dSPACE system. The preformed static pressure control tests, confirmed applicability of tube actuator in flapper nozzle type valves. Obtained results were compared with simulation model prepared in Matlab Simulink software. Streszczenie. Artykul zawiera opis konstrukcji, badania statyczne i modelowanie zaworu typu dysza przyslona. Autorzy zaprezentowali badania piezo rurki model PT230, ktorej cechą charakterystyczną jest mozliwośc odksztalcenia w dwoch kierunkach. Praca ta jest przygotowaniem do konstrukcji nowego zaworu elektropneumatycznego. Badania zostaly wykonane na specjalnie w tym celu wykonanym stanowisku zawierającym zawor, ktorym zastosowano piezo rurke jako przyslone. Procesy akwizycji danych oraz sterowania wykonane zostaly w systemie dSPACE. Przeprowadzone badania statyczne sterowania ciśnieniem wyjściowym, potwierdzają mozliwośc zastosowania piezo rurki w zaworach typu dysza przyslona. Zarejestrowane wyniki poddano porownaniu z modelem przygotowanym w oprogramowaniu Matlab Simulink. (Zawor pneumatyczny typu dysza przyslona z rurką piezoelektryczną jako elementem zadającym)

Study on the Control System of Grinding the Nozzle of Twin Flapper-Nozzle Valve

In this paper, neural network and grey fuzzy control technology are applied in Abrasive Flow Machining (AFM) to grind the mico-hole in th nozzle of the twin flapper-nozzle valve. An intelligent control system with fine tuning working pressure is established that can predict the process parameters automatically before machining and forcast the flow to adjust the working pressure in machining.The result of experiment indicates that this system has high level of intelligent and can get very high machining accuracy.

Degradation assessment and life prediction of electro-hydraulic servo valve under erosion wear

Abstract This paper presents a degradation assessment and life prediction method for electro-hydraulic servo valve (EHSV). Unlike traditional statistical methods, our work is motivated by the failure mechanism of erosion wear. The degradation of performance characteristic was related with structure wear in twin flapper–nozzle valve and spool valve. Mathematic models of turbulent and erosion wear were established by the combined technologies of computational fluid dynamics and erosion theory. By visual simulation, we analyzed the erosion wear distribution and erosion wear rate under different contaminated oil conditions and working missions. Furthermore, degradation models of performance characteristic were built according to degradation trends of system performance under different erosive wear stages. Finally, the assessment results show that: (1) Hydraulic oil with contaminant particles will distinctly erode the sharp edges of valve bushing and spool. Besides, the erosion rate depends on valve structure and port opening size. (2) Wear at sharp edges of spool valve influences pressure gain, null leakage flow and lap. Furthermore, these performance indicators are monotonically degraded. With the definition of failure for the EHSV, the service life is 9000 missions by our simple mission profile.

Modeling and Dynamic Evaluation of a Two-Stage Two-Spool Servovalve Used for Pressure Control

Experimental results for a unique design of a two-spool pressure control valve were reported by Anderson (1984). The first stage is a dynamically stable flapper-nozzle valve for which a mathematical model is already available (Lin and Akers, 1989a). For the second stage, however, which consists of two parallel spools in a common body, no such model existed. The purpose of this paper was therefore to construct such a model and to compare results calculated from it to experimental values. Moderately good agreement with experimental values was obtained.

Nonlinear Dynamics of an Electrohydraulic Flapper Nozzle Valve

A nonlinear model of an electrohydraulic flapper-nozzle valve is developed, using an energy-based approach. Nonlinearities are found in the resistances, compliances, and the inertances; the latter produce state-dependent coupling terms. The model is applied to a valve designed for pulse-width modulation (PWM). Most model parameters are derived from a priori design parameters, but some were found from a series of experiments which also served to confirm the model. The valve and its model responded satisfactorily to PWM signals up to 500 Hz.

The Use of Interferometry as an Aid to Studying Flapper-Valve Flow Characteristics

A technique is described for visualizing the air flow over a surface by means of an oil film. The technique is used in conjunction with experimentally determined flapper-plate pressure profiles to examine the flow characteristics of a flapper-nozzle valve used to control air at 425 kPa (4.25 bar). The oil film shows clearly the points of separation and reattachment of the air boundary layer resulting from shock wave and boundary layer interaction. Possible applications of the technique are discussed and attention is focused on the use of the oil-film technique in conjunction with interferometry as a tool for the rapid determination of the effects caused by changes in nozzle geometry.

Further Study of a Low-Pressure on-off Pneumatic Servomechanism

This paper compares experimental and theoretical transient and frequency response results for a low-pressure on-off pneumatic servomechanism comprising a polarized relay with dead zone and hysteresis operating a four-way flapper-nozzle valve via a torque-motor. The valve operates a linear pneumatic motor which drives a load in the presence of Coulomb friction and stiction. Position, velocity, and quasi-transient pressure feedback are provided. The effect of dynamic conditions on the valve characteristics is discussed.

A Step-Bearing Accelerometer With Pneumatic Signal Output

A novel pneumatic acceleration sensor utilizing a single gas-bearing supported element is described. System damping and pneumatic signal output are obtained by reverse-flow flapper-nozzle valves which act as negative springs with respect to the inertial mass. Approximate design relationships for the static and dynamic performance of a two-axis accelerometer are presented. A prototype unit built to verify feasibility is described and experimental results are presented and compared with the analysis.

A New Type of Pneumatic Triangle Wave Oscillator

A new type of pneumatic oscillator is presented which produces triangular waveforms of pressure versus time. The device can be used for both high power and low power applications. It utilizes a freely floating disk which translates back and forth a short distance inside a housing between two dynamically unstable flapper nozzle valves. A theoretical analysis of the performance and stability of the device is given. A simplified analysis and design procedure which accounts for load flow is shown. Several prototype units were successfully operated and the experimental results obtained with them are described and compared with the predicted results.

Static and Dynamic Control Characteristics of Flapper-Nozzle Valves

A basic study was conducted on a flapper-nozzle hydraulic control valve to explore in detail its static and dynamic control characteristics. These static and dynamic control characteristics are presented and both the theoretical and experimental results compared. Correlation between the theoretical and experimental results were found to be quite good.

Closure to “Discussions of ‘Static and Dynamic Control Characteristics of Flapper-Nozzle Valves’” (1959, ASME J. Basic Eng., 81, pp. 282–284)

Closure to “Discussions of ‘Static and Dynamic Control Characteristics of Flapper-Nozzle Valves’” (1959, ASME J. Basic Eng., 81, pp. 282–284)