Valve Orifice Research Articles

Numerical Analysis of the Factors Influencing the Erosion of the Valve Port of a High-Speed On/Off Valve

Aiming at the problem of valve port erosion caused by contaminated particles, a three-dimensional prediction model of valve orifice erosion was established based on computational fluid dynamics (CFD) and erosion theory, considering the influence of the valve port eddy current on the oil flow. The discrete phase model (DPM) of fluent is used to obtain the orifice erosion location and erosion rate, and the causes of erosion of the high-speed on/off valve are analyzed. On this basis, several factors influencing valve port erosion are simulated to investigate the relationship between particle collision behavior and valve port erosion morphology under different factors, and the change rule of valve port erosion under different factors is analyzed. The results show that the high-speed on/off valve service life decreases with a larger cone angle of the spool, a larger pressure difference at the valve port, a larger proportion of large particle contaminants in the oil, a higher oil contamination level, and a larger filter aperture. In addition, the grey relational analysis method is used to clarify the pressure difference at the valve port, the particle size, and the filter aperture as the three most important factors affecting the erosion of the valve port of a high-speed on/off valve.

Treatment of secondary mitral regurgitation by transcatheter edge-to-edge repair using MitraClip.

Transcatheter edge-to-edge repair (TEER) is becoming the standard invasive treatment for ventricular functional mitral regurgitation (MR). It is necessary to determine the severity of MR before treatment with MitraClip; however, the severity of secondary MR is usually underestimated compared with that of primary MR and varies temporally. Therefore, to accurately determine the severity of MR, it is important to correctly use the algorithm of the guidelines for valvular heart disease and aggressively perform stress echocardiography. Before performing TEER, the difficulty of the procedure should be evaluated. First, morphological features that make TEER unsuitable, such as cleft of the mitral leaflet, mitral stenosis (MS), or perforation of the mitral leaflet, should be checked. The mitral valve orifice area, transmitral valve pressure gradient, coaptation depth, coaptation length, and posterior leaflet length should be measured to determine the difficulty of the procedure based on the inclusion criteria of Endovascular Valve Edge-to-Edge Repair Study II and the German consensus. After MitraClip implantation, in addition to assessing the severity of MS and residual MR, the pulmonary venous flow pattern and stroke volume should be evaluated to comprehensively assess whether TEER improves the hemodynamics. MitraClip has also been used to treat atrial functional MR, another type of secondary MR. Several reports suggest that MitraClip is effective for atrial functional MR; however, evidence is still being accumulated.

High-gain observer-based pump/valve combined control for heavy vehicle electro-hydraulic servo steering system

Electro-hydraulic servo steering system (EHSSS) has been widely used in multi-axle heavy vehicles. Noteworthy, the traditional EHSSS controlled only by servo solenoid valve has amounts of energy loss in throttling orifice. Although the steering control accuracy is ensured, it leads to low energy efficiency. In this paper, a novel pump/valve combined control (PVCC) EHSSS is proposed to increase the energy efficiency, which only uses one servo motor pump and one servo solenoid valve to drive the steering trapezoid mechanism. Based on the control objectives of low pressure difference in valve orifice and high steering tracking performance, a dual-input-dual-output control strategy is proposed. To guarantee the high steering tracking performance of PVCC steering system, a high-gain observer based sliding mode controller (HGO-SMC) is designed for controlling the spool displacement of servo solenoid valve. During the steering process, the servo motor pump is controlled by a simple speed feedforward and PID controller, so that the pressure difference in throttling orifice is kept at a low value to reduce the energy wasted. The experimental comparison results show that the proposed method can achieve the same tracking performance as valve control EHSSS with less energy consumption.

Leaflet Resection vs Preservation for Degenerative Mitral Regurgitation: Functional Outcomes and Mitral Stenosis at 12 Months in a Randomized Trial.

Mitral valve repair is the gold standard treatment for degenerative mitral regurgitation (MR). The Canadian Mitral Research Alliance (CAMRA) CardioLink-2 trial showed no significant association between repair strategy, that is, leaflet resection vs preservation, and risk of functional mitral stenosis. In this subanalysis, we compared outcomes and functional tests at 12 months. CAMRA CardioLink-2 was a multicentre randomized controlled trial that allocated patients with degenerative MR and posterior leaflet prolapse to leaflet resection (n= 54) or preservation (n= 50). Stress echocardiography and functional status assessments, including the 6-minute walk test, were compared 12 months after repair. Baseline demographics, stress echocardiographic findings, and mitral annuloplasty prosthesis size (33.0 ± 3.0 vs 33.6 ± 3.4 mm; P= 0.4) were similar between the two groups. There were no readmissions for heart failure or deaths during the follow-up period. At 12 months, a larger percentage of patients were in NYHA functional class ≥ 2 in the resection group compared with the preservation group (P= 0.01). Exercise capacity, rate-pressure product, 6-minute walk distance, and mean mitral valve gradients were not significantly different between the groups at 12 months. A more prominent increase in mean mitral gradient with smaller annuloplasty sizes was observed in the resection group at both rest (P= 0.03) and peak exercise (P= 0.005) in the linear regression model. At 12 months, there were no significant differences in mitral valve gradient, exercise capacity, and 6-minute walk test between repair strategies. Leaflet preservation may offer a larger mitral valve orifice with improved gradients in patients requiring smaller annuloplasty sizes.

Immediate and Short-Term Variations in the Echocardiographic Cardiac Hemodynamic Parameters after the Transcatheter Atrial Septal Defect Device Closure and its Procedural Success.

Background and Aims:Transcatheter closure of the secundum atrial septal defect (ASD) has become an accepted alternative to surgical repair. We aimed to analyze and compare the changes in cardiac hemodynamics with transthoracic echocardiography (TTE) before, within 48 hours, and after 3 months of ASD closure.
 Methods: This was a prospective, single-centered study of 43 patients who underwent ASD device closure in the Manmohan Cardiothoracic Vascular and Transplant Center during June 2020 to June 2021 with Amplatzer Septal Occluder under transesophageal and fluoroscopic guidance. The patients were evaluated with TTE before, at 48 hours, and 3 months after the procedure.
 Results: At 48 hours and 3 months of device closure, the right atrial major dimension, the maximum blood flow velocity at the pulmonary valve orifice, mean flow velocity, velocity time integral, and E peak and A peak blood flow velocity at the tricuspid valve orifice were significantly reduced (P < 0.001). At 3 months, the dimensions and ejection fraction of the left ventricle showed significant increment (P < 0.001). Likewise, the right atrial minor dimension and area, right ventricular basal, mid, and longitudinal dimensions, tricuspid annular plane systolic excursion, right ventricular Tei Index, and fractional area change were significantly reduced (P < 0.001). The main pulmonary artery diameter, pulmonary artery systolic and mean pressure, and the pulmonary vascular resistance and index were significantly reduced (p <0.001). The procedural success rate was 97.6%.
 Conclusion: Echocardiographic evaluation demonstrated that cardiac hemodynamics and loading conditions improved significantly at 3 months after percutaneous closure of ASD. The transcatheter closure of ASD was safe with good short-term outcomes.

Fluid-Structure Interaction Analysis on the Influence of the Aortic Valve Stent Leaflet Structure in Hemodynamics.

Transcatheter aortic valve replacement (TAVR) is a minimally invasive surgical treatment for heart valve disease. At present, personalized TAVR valves are not available for some patients. This study adopts the fluid-structure interaction (FSI) model of the research object that has a three-disc leaflet form and structural design in the valve leaflet area. The valve opening shape, orifice area, stress-strain, and distribution of hemodynamic flow and pressure were compared under the condition of equal contact area between valve and blood. The FSI method was used to simulate the complex three dimensional characteristics of the flow field more accurately around the valve after TAVR stent implantation. Three personalized stent systems were established to study the performance of the leaflet design based on computational fluid dynamics. By comparing the different leaflet geometries, the maximum stress on leaflets and stents of model B was relatively reduced, which effectively improved the reliability of the stent design. Such valve design also causes the opening area of the valve leaflet to increase and the low-velocity area of the flow field to decrease during the working process of the valve, thus reducing the possibility of thrombosis. These findings can underpin breakthroughs in product design, and provide important theoretical support and technical guidance for clinical research.

Feasibility of endoscopic submucosal dissection for cecal tumors involving the ileocecal valve or appendiceal orifice.

Endoscopic resection of the ileocecal valve lesions (ICVL) and peri-appendiceal orifice lesions (PAOL), is challenging. This study aimed to evaluate the feasibility of endoscopic submucosal dissection (ESD) for ICVLs and PAOLs compared with other cecal lesions (OCEL). This was a multicenter, retrospective cohort study conducted at a cancer center hospital and two community hospitals. Non-pedunculated cecal lesions that were intended to be treated by ESD followed by at least one surveillance colonoscopy were included. The main outcome was curative resection defined as en-bloc resection and R0 resection without risk factors of metastases. The secondary outcome was co lon preservation. A total of 206 patients with 206 cecal lesions, including 37 ICVL, 27 PAOL, and 142 OCEL, who were to be treated with ESD were included in this study. Curative resection rates were 75.7% for ICVL, 70.4% for PAOL, and 77.5% for OCEL (P=0.67). In the multivariate analysis of predictors of curative resection, tumor size (<40mm) (odds ratio [OR] 2.40; 95% confidence intervals [CI], 1.14-5.04; P=0.02) and a negative non-lifting sign (OR 6.12; 95% CI, 2.55-14.60; P<0.01) were significant. Colon preservation was achieved for 91.9% of the ICVL, 92.6% of the PAOL, and 90.8% of the OCEL (P=0.947). Based on curative resection and colon preservation rates, ESD was found to be feasible for ICVL and PAOL. Large tumor size (≥40mm) and positive non-lifting signs were significant factors for non-curative resection.

Experimental parametric analysis of vapour condenser for vacuum drying application

The experimental parametric investigation on a vapour condenser under vacuum conditions for the vacuum drying application has been presented. The mixture of air-vapour and the non-condensates are extracted from the system using a vacuum condenser. Hence, the vapour's behaviour inside a condenser becomes a subject of study exposed to different operating conditions. In the current study, parameters considered are condenser pressure (20 and 70 mbar), inlet valve orifice diameter (10 and 8 mm), and the cooling water flow rate through the pipes (32 lpm and 16 lpm). The condensation rate increases with the shell pressure and seems to remain unaffected by the chilling water flow rates. The turbulence in the steam flow increases with the increase in the shell pressure. The fluids flowing through tubes at low-velocity experience smaller pressure drops and show low heat transfer coefficients. The reproducibility and repeatability of the tests are excellent.

Risk of Stroke With Mitral Stenosis: The Underlying Mechanism, Treatment, and Prevention.

Mitral stenosis (MS), a valvular heart disease, is defined by the narrowing of the mitral valve orifice. The common risk factors for stroke include mitral annular calcification (MAC), diabetes mellitus (DM), male gender, hypertension (HTN), hyperlipidemia, and obesity. Endothelial damage, hypercoagulability, and blood stasis in the left atrium promote the development of the thrombus. Among all the risk factors described, MAC is the independent predictor of stroke. The complicated mechanisms responsible for thromboembolism, predisposing factors for thromboembolism, the risk of cerebrovascular accident (CVA) in MS patients, advanced standardized assessment models for identifying those at risk for stroke, and the possible advantages and disadvantages of available therapies have all been discussed in this review article. We have also discussed newer oral anticoagulants (NOACs) like dabigatran, edoxaban, apixaban, and rivaroxaban. Non-pharmacological therapies are also highlighted such as left atrial appendage ligation and occlusion devices. We also conducted a thorough review of the literature on the efficacy and safety of various NOACs in reducing the risk of stroke.

Clinical and echocardiographic differences in three different etiologies of severe mitral stenosis.

In our institute, the causes of mitral stenosis (MS) are generally categorized into three main etiologies-rheumatic MS (RMS), degenerative MS with annular and leaflet calcification, and post-clip MS as a consequence of transcatheter mitral valve repair with clips for treating mitral regurgitation. However, clinical differences among the three etiologies are uncertain. We retrospectively assessed 293 consecutive patients (53 with RMS, 118 with degenerative MS, and 122 with post-clip MS) who had a three-dimensional (3D) transesophageal echocardiography (TEE) derived mitral valve orifice area (MVA) of ≤1.5cm2 , and a mean transmitral pressure gradient of ≥5 mmHg on transthoracic echocardiography. Although there was no difference in 3D-TEE-derived MVA among the three groups, patients with post-clip MS had a significantly lower mean transmitral pressure gradient compared to those with either of the other two types of MS (10.8 ([7.9-15.2] mmHg vs. 9.6 [7.3-12.5] mmHg vs. 6.9 [6.0-9.2] mmHg; p<.001). Patients with RMS had a higher prevalence of dyspnea. The independent determinants of dyspnea were pressure half time in RMS, 3D-TEE-derived MVA and estimated right atrial pressure in degenerative MS, and left ventricle ejection fraction in post-clip MS. Patients with post-clip MS had the lowest mean transmitral pressure gradient, and patients with RMS had the highest prevalence of dyspnea, despite having a similar 3D-TEE-derived MVA. The determinants of dyspnea were different among the three etiologies of MS.

Valve control of a hydraulically interconnected suspension system to improve vehicle handling qualities

This paper deals with the control of a hydraulically interconnected suspension system to improve the handling performance of the vehicle. A seven-degrees-of-freedom MATLAB/Simulink vehicle model and an Adams/Car model are used for simulation purposes. A Simscape model for analysing the hydraulic subsystem is also employed. It was observed that the yaw rate and roll responses of the vehicle are influenced to a large extent by the flow control valve opening values. The handling performance of the vehicle was investigated by the control of the orifice valves and their adjustment according to the lateral acceleration inputs. Considerable improvements were obtained in the handling qualities without sacrificing the ride responses, compared to the responses of a passive interconnected suspension.

Numerical study on the behavior and design of a novel multistage hydrogen pressure-reducing valve

Applying hydrogen fuel-cell vehicles (HFCVs) is feasible to achieve net zero carbon emission in transportation sector. The energy density requirements of these vehicles are fulfilled via high-pressure gaseous hydrogen storage; therefore, an effective pressure-reducing system is necessary. In this work, a novel multistage pressure-reducing valve (named as T–M valve) combining a sleeve pressure structure valve and a Tesla-type orifice valve is proposed. A computational fluid dynamics (CFD) model is developed to analyze the influence of operating parameters on pressure and velocity distributions. Results show that the large pressure and velocity gradients’ region is concentrated on the throttling elements. The valve opening and pressure ratio significantly affect energy consumption. In addition, the Mach number in the valve less than one is proposed. This study is conducive to further energy conservation and emission reduction and the research of multistage flow pressure-reducing devices. •A novel multistage hydrogen pressure-reducing valve using a sleeve pressure structure and Tesla-type orifice valves. •Analyze the novel valve behavior using a computational fluid dynamics model. •Large pressure and velocity gradients area is concentrated on the throttling elements. •The valve opening and pressure ratio significantly affect energy consumption.

A novel “proximal first” Inoue balloon catheter for retrograde aortic valvuloplasty: Initial case report

The Inoue balloon, invented for percutaneous transseptal mitral commissurotomy for mitral stenosis, is initially dilated in the distal portion and then the proximal portion, forming an hourglass shape that stabilizes the balloon at the mitral valve orifice with a pulling action. The device has been successfully applied to antegrade aortic valvuloplasty; the hourglass shape stabilizes the balloon across the aortic valve without rapid ventricular pacing. Subsequently, an Inoue balloon was developed for retrograde aortic valvuloplasty using the same design as the antegrade balloon. The hourglass-shaped balloon, however, has difficulty maintaining stability across the aortic valve because the distal portion of the balloon, which inflates first, directly receives systolic pressure from the left ventricle. A novel Inoue balloon was invented to overcome this issue by altering the manner of inflation: the proximal portion inflates first, followed by the distal portion. Theoretically, the proximal portion, which initially inflates just above the aortic valve, remains secure across the valve by applying a pressing force that counteracts the systolic forward pressure. Furthermore, a radiopaque marker is placed at the center of the balloon to enable rapid and precise balloon adjustment. We present a case involving a 65-year-old female hemodialysis patient with severe symptomatic aortic stenosis who we successfully treated with balloon aortic valvuloplasty using the novel Inoue balloon followed by transcatheter aortic valve implantation. The present case demonstrates the feasibility and effectiveness of the novel "proximal first" Inoue balloon for retrograde balloon aortic valvuloplasty for severe aortic stenosis.

Bicuspid aortic valve morphology and hemodynamics by same-day echocardiography and cardiac MRI.

This study investigated the impact of bicuspid aortic valve (BAV) on valve morphology and motion as well as proximal and aortic hemodynamics using a same-day echocardiography and cardiac MRI. Transthoracic echocardiography, two-dimensional cine MRI of the aortic valve, and aortic 4D flow MRI were performed on the same day in 9 normofunctional BAV patients (age = 41 ± 12, 3 female), 4 BAV with moderate to severe aortic stenosis (AS) (age = 63 ± 5, 1 female), and 36 healthy tricuspid aortic valve controls (age = 52 ± 10, 21 female). Valve opening and closing timings and transvalvular peak velocity were measured using B-mode and Doppler echocardiogram, respectively. Valve orifice morphology at a fully-opened state was characterized using cine MRI. Ascending aortic (AAo) wall shear stress (WSS) was measured using 4D flow MRI data. Valve motion timings were similar between BAV and controls. BAV was associated with an increased orifice aspect ratio (1.44 ± 0.11 vs. 1.10 ± 0.13, P < 0.001), transvalvular peak velocity (1.5 ± 0.3 vs. 1.2 ± 0.2m/s, P < 0.001) and maximum AAo WSS (1.62 ± 0.31 vs. 0.91 ± 0.24Pa, P < 0.001). The increased orifice aspect ratio was associated with the increase in transvalvular peak velocity (r = 0.80, P < 0.0001) and maximum AAo WSS (r = 0.83, P < 0.0001). Transvalvular peak velocity was also positively correlated with maximum AAo WSS (r = 0.83, P < 0.0001). A same-day echo and MRI imaging allows for a comprehensive assessment of the impact of aortic valve disease on valve function and hemodynamics. In this pilot application to BAV, we found increased orifice aspect ratio may be responsible for increased transvalvular peak velocity and maximum AAo WSS.

Measurement of the mass-flow-rate characterization parameters of high-pressure pneumatic servo slide valves

The mass-flow-rate characteristics of high-pressure pneumatic servo valves (HPSVs) have an important effect on the dynamic performance of high-pressure servo systems. However, these characteristics are difficult to obtain by theoretical calculations and flowmeter measurements owing to the compressibility of high-pressure gas. In this paper, a new measurement method of the mass-flow-rate characterization parameters of HPSVs is proposed based on the principle of the series connection sonic discharge of valve orifices. The effective cross-sectional area and critical pressure ratio of the servo valve orifices can be accurately and efficiently determined by connecting two valve orifices in series and exchanging the flow sequence of the two valve orifices. The two assumptions including the sonic and adiabatic discharge of the proposed measurement method were verified. A comparison between the test and simulation data showed that the accuracy of the measured effective cross-sectional area and critical pressure ratio of the HPSV was high. The measured critical pressure ratio ranged from 0.46 to 0.50, and the flow coefficient represented by the effective cross-sectional area variation decreased with increasing valve opening. These findings have general implications for the accurate design, analysis, and control of high-pressure pneumatic servo systems.

Coronary Artery Origins Pattern in Pediatric Patients with Right-Left Fusion Bicuspid Aortic Valve.

Bicuspid aortic valve (BAV) is a common congenital heart defect associated with coronary artery (CA) variants, including higher incidence of left CA dominance and shorter left main CA length. We observed by transthoracic echocardiography that left and right CA origins appear closer together in pediatric patients with right-left fusion (R/L) BAV compared to patients with trileaflet aortic valves. We sought to objectively confirm this observation. A retrospective review of pediatric echocardiograms with R/L BAV at a single institution (12/2010-11/2018) was performed. The 'coronary angle' was defined as the angle between the left and right coronary artery origins in the parasternal short axis view relative to the center of the aortic valve orifice. Values were compared to age-matched controls. Patients with inadequate images, anomalous coronary origins, or predefined significant congenital heart defects were excluded. We compared 191 R/L BAV patients (64% male) to 136 controls (57% male). Coronary angle was significantly more acute in R/L BAV than in controls (117.9° ± 16.7° vs 139.0° ± 10.1°, p < 0.0001). This was independent of age and gender. The difference persisted when BAV patients with abnormal aortic annulus/root diameters were removed from analysis (119.5° ± 15.1° vs 139.0° ± 10.1°, p < 0.0001). CA origins are closer together in R/L BAV independent of age, gender, or annulus/root size. This new anatomical description may aid in the diagnosis of subtle ('forme fruste') R/L BAV, assist in interventional planning, and improve understanding of the relationship between BAV and CA development.

Mathematical modeling and experimental investigation of a rotary valve generating sinusoidal pressure signals based on fan-arc-straight orifice

The continuous-wave mud pulse telemetry is currently one of the most advantageous methods for wireless downhole transmission. The rotary valve orifice of a continuous-wave mud pulser must be optimized to generate highly similar sinusoidal pressure waves for high-speed and reliable transmission. In this study, an improved fan-arc-straight-based valve orifice is designed based on a general fan-based valve orifice by analyzing the relationship between throttle area and relative rotation angle of the rotor/stator on the basis of thin-walled cutting edge differential pressure generation mechanism. Then, CFD simulation studies are investigated. It is indicated that the peak-to-peak value of the differential pressure is proportional to the square of the inlet flow; and with the increase of axial clearances between the stator and rotor, the peak-to-peak values of the differential pressure signals show a negative exponential decrease trend, while the correlation coefficients also decrease monotonously. Furthermore, surface hydraulic system experiments have also been implemented; and the actual 8 Hz and 12 Hz pressure waves with correlation coefficients greater than 0.99 are obtained compared with the corresponding sinusoidal signals. It is believed that the optimized valve can achieve highly similar sinusoidal pressure waves with acceptable amplitudes during practical operation to meet the field operation requirements. • An improved fan-arc-straight-based valve orifice is designed based on a general fan valve orifice. • CFD simulations investigate features of the differential pressure signals. • Actual 8 Hz and 12 Hz pressure waves with correlation coefficients greater than 0.99 are obtained.

Three-dimensional echocardiography for predicting mitral stenosis after MitraClip for functional mitral regurgitation.

Postprocedural mitral stenosis (MS), or increased transmitral mean pressure gradient (TMPG), is one of the limitations of transcatheter edge-to-edge mitral valve repair using MitraClip (Abbott Vascular Inc., Santa Clara, USA); however, the usefulness of three-dimensional transesophageal echocardiography (3D-TEE) for predicting postprocedural MS in functional mitral regurgitation (MR) has not been fully elucidated. Eighty-two consecutive functional MR patients who underwent transcatheter mitral valve repair using MitraClip were retrospectively studied. Postprocedural MS was defined as TMPG ≥ 5mmHg by echocardiography. Ten patients had postprocedural MS, and 3D-TEE showed that patients with postprocedural MS had smaller preprocedural mitral valve orifice area (MVOA), anteroposterior and mediolateral diameter, leaflet area, and annulus area. Receiver operating characteristic analysis showed that leaflet area (area under the curve (AUC) 0.829), annulus area (AUC 0.813), anteroposterior diameter (AUC 0.797) and mediolateral diameter (AUC 0.803) evaluated using 3D-TEE were predictors of postprocedural MS, and their predictive abilities were higher than those of preprocedural MVOA (AUC 0.756) and preprocedural TMPG (AUC 0.716). Adding leaflet area to TMPG and MVOA resulted in higher C-statistics for predicting postprocedural MS (from0.716to0.845 and from0.756to0.853, respectively). In functional MR patients treated with MitraClip, leaflet area and annulus area evaluated using 3D-TEE had high predictive values for postprocedural MS, and their predictive abilities were higher than those of preprocedural TMPG or MVOA.

A State-of-the-Art Review on Two-Phase Flow-Induced Noise in Expansion Devices

This paper presents a state-of-the-art review of the literature concerning flow-induced noise in expansion devices. The topics covered are theoretical natural frequency models of bubbles with spherical and cylindrical shapes and flow-induced noise in capillary tubes, such as orifice, thermal and electric expansion valve. Several parametric conditions affect the flow-induced noise in capillary tubes, such as outlet capillary geometry, capillary inner diameter and length, flow orientation, outlet vapor quality, mass velocity, pressure drop, in/outlet flow pattern, evaporation temperature, and refrigeration cycle operational conditions. Despite the broad use of orifice, there is a lack of knowledge in the literature of flow-induced noise in these devices. The flow-induced noise seems primarily a function of mass velocity, vapor quality, and flow pattern. It seems that outlet intermittent flow patterns lead to significant noise in capillary tubes and expansion valves. In general, for the noise evaluated outside the expansion device, electric expansion valves exhibited higher sound pressure levels than capillary tubes. Furthermore, the present literature review indicates that efforts should be made to perform tests for a wide range of conditions evaluating the noise within and outside the expansion device, device wall acceleration and flow topology for current and new refrigerants, simultaneously.

OPTIMIZATION OF PARAMETERS OF THE MOBILE MACHINE ADAPTIVE HYDRAULIC CIRCUIT

Mobile machine hydraulic circuits tend to adopt electrohydraulics. Such hydraulic circuits are based on controlled pumps, modulated hydraulics, sensors and controllers. This allows adapting the hydraulic circuit operating modes to the changes of external conditions of the machine operation. Application of hydraulic circuits with electrohydraulics in mobile machines allows to use mobile machines efficiently with a high number of removable endangers, increases their performance and improves the quality of performed works. The authors propose an adaptive hydraulic circuit for a mobile machine. The operation process in the adaptive hydraulic circuit in static and dynamic modes is determined by the interaction of the pump controller and pressure differential control valves. The hydraulic system operation stability, its fast response and readjustment are determined by the controller parameters. It has been revealed that the main parameters affecting the dynamic characteristics of the hydraulic system are: throttle area and coefficient of amplifying the pump controller orifice, dampener area and coefficient of amplifying the pressure differential control valve orifice. These parameters affect the stability, controlling and readjustment time in the hydraulic circuit differently. A functional including the values of controlling time , σ controlling and losses in the pump controller was used as an optimization criterion. The optimization has been made according to the developed mathematical model applying the method developed by I. Sobol and R. Statnikov. During the optimization each controller parameter changed on 3 levels. 81 tests were made and the best combination of controller parameters for the optimization criterion was determined. The following hydraulic circuit operation values were reached under the optimal values of parameters = 1.0·10-6 m2, = 1.0·10-3 m, = 1.2·10-6 m2, = 10·10-3 m: = 1.1 с, σ = 32 %, = 0.82 kW that comply with the requirements towards hydraulic circuits of mobile machines.