Many industries including power-plants, refineries and so on are using high pressure Control valves. Many of these valves have traditional geometries like butterfly valves. Unfortunately, because of the special design of these valves, cavitation causes very rapid corrosion. In the last decade, a next generation of Control valves have been introduced which are designed to prevent cavitation. Because of the special fluid paths in the Labyrinth valves, the pressure drop is very graduated which prevents cavitation. In this article, the geometry of fluid path is optimized using Taguchi method. To this end, four parameters are considered including path's height, number of corners, corner radii and input area. For each parameter three levels are assumed and using a standard Taguchi array the optimum geometry is predicted. Then the pressure drop in optimum geometry is simulated using finite element method and the results validated the optimized geometry.

This paper presents the sensitivity analysis of a sample hydraulic servo valve. The sensitivity of the flow-current curve with respect to variations of geometrical and functional parameters is evaluated. This analysis is done by use of a model which simulates the valve behavior in terms of geometrical parameters and properties of components. With attention to multiplicity of the valve components and the complexity of the system, the more effective parameters have been studied more precisely. Deviation of “flow gain” And “saturation flow” -which are the main characteristics of the valve behavior- from their nominal values in the flow-current curve, is the criterion for the valve sensitivity assessment. The curve of characteristic variations versus parameter variations has been plotted. The evaluations indicated that all of the sensitivity curves are linear in the limited intervals. Also between the evaluated parameters, “nozzle-flapper equilibrium distance”, “orifice diameter” and “stiffness of spool spring” have more sensitivity effect on the valve performance, respectively.

A compressor is a machine that is used to increase the pressure of various gases. How to increase the pressure depends on the compressor type. One of the functional problems of centrifugal compressors is the phenomenon of the surge, which is still an obscure and unknown phenomenon that can induce mechanical or thermal stress in the system and cause a lot of damage. This type of aerodynamic instability reduces the compression ratio at both ends of the compressor, thereby reducing the overall efficiency of the system. In general, when a surge occurs, it causes process turbulence, the degradation of overall compressor efficiency, the reduction of compressor life due to mechanical damage to seals, bearings, rotor, and impellers, and the loss of internal freedoms and sensitive mechanical parts of the system. Therefore, surge Control is one of the challenges of compressor Control and expands the operating range of compressor operation. A map compressor consists of two axes, horizontal and vertical, as well as a set of curves that show the horizontal axis of the flow (capacity) and the vertical axis, head or pressure. Compressors must change their speed to change the output flow. For each speed, there is a minimum point and a maximum flow point within which the compressor operation is stable and predictable. The maximum capacity point is called the stone wall point and the minimum capacity point is called the vertex point. The surge line (SL) of a compressor is formed by connecting the surge points at different speeds. If the compressor works on the right side of the surge line, it is in a steady state, but if it works on the left side of the surge line, it is in an unstable or surge state. Using methods based on active surge Control, the instabilities leading to the surge can be eliminated, and the area of stable performance of the system can be extended to the surge line, and thereby the stable area of the system can be widened. This paper uses a dynamic model of centrifugal compressors with a recycle valve, as well as a proportional-integrator-derivative (PID) Controller and a sliding mode Controller, to Control the surge phenomenon with a compressor Control approach based on the surge Control line. A new sliding surface is defined for Controlling sliding mode, and it is Controlled by using recycle valve and a compressor inlet valve. A quadratic Lyapunov function is used to ensure the stability of the intended slip surface. The two approaches of inlet and recycle valve are expressed individually and collectively. The results of simulation in MATLAB state that among the compressor with a PID Controller and the compressor with sliding mode, the latter outperforms the former in Controlling the compressor at different speeds. Based on the comparison of the results, the amplitude of the Control signal in the sliding mode is less than PID and the system reaches a stable state with less energy consumption, which shows better Control by the sliding mode than by PID.

Introduction: Water distribution uniformity is a key in pressurized irrigation systems. Pressure fluctuations due to topographical changes, local and frictional head losses, and different water uses are considered of great concerns. Any mechanical device with the ability to keep an almost constant flow delivery, irrespective of the pressure fluctuations is of great practical importance. In this regard, a flow Control valve is a useful tool. A flow Control valve is a mechanical choked orifice plate structure including a float-spring mechanism inserted in an ordinary orifice (Zhang and Wang 2015). Such a valve is not yet produced commercially. In this study, the effect of the spring elasticity mainly due to spring fatigue is investigated experimentally on the valve performance. Also, the changes in the installation location of the float, when the valve is in rest condition, may affect its performance. To quantify this effect a detailed experimental plan was performed...

Automatic line-break Control valve can be used in zones with no access to national electricity network، hazardous or impassable area enclosure، for passive defence conditions or to protect di erent ecosystems such as rivers and ground water، forests and fertile land and etc. The pipeline break causes a growth in oil velocity magnitude and uid pressure reduction consequently but the pressure drop is not a good signal for line break detection because it is low، therefore reference tank is used. The reference tank is connected to the pipeline through a calibrated orice with check valve. The tank pressure is higher than pipeline pressure when pressure reduction occurs by line breaking. If the pressure di erence between tank and pipeline is higher than the sustainable pressure value of diaphragm valve، the valve will be closed by actuator. In this paper، the e ects of orice diameter، pipeline initial pressure and pipeline break pressure drop rate on the di erential pressure of diaphragm valve in automatic line-break Control valve have been studied with nitrogen by 27 experiments. The di erential pressure of diaphragm valve is increased by the growth of pipeline break pressure drop rate. The occurrence time of maximum di erential pressure of diaphragm valve just depends on orice diameter. The maximum of di erential pressure increases with decrease of orice diameter. The di erential pressure of diaphragm valve increases by decrease of pipeline initial pressure for constant orice diameters and pipeline break pressure drop rates. The curves of maximum di erential pressure generated by di erent pipeline break pressure drop rates are shown for di erent orice diameters and pipeline initial pressure. The values of curves in this diagram with 10 percent safety factor can be used in automatic line-break Control valve setting which are installed on gas transportation pipelines because of the nitrogen gas using instead of the natural gas.

Flow behavior through a gas turbine double-container fuel valve is numerically studied. Normally the gas fuel supply pressure of the gas turbine sites is over 20+ barg while the combustion chamber pressure is around 12 barg in base load operation and slightly more than atmospheric during start-up. Therefore, the flow Control through this high range of pressure ratios is a very difficult and costly task with a single-container Control valve. The double-container valve is an innovative design which consists of two parts, SRV (Stop Ratio valve) followed by GCV (Gas Control valve), in a compact unit. SRV maintains a significantly low pressure upstream of the GCV during gas turbine firing to establish flame and Control fuel flow during acceleration. It opens the GCV to a position where it is much easier to Control the flow through the valve. The same situation exists in base load operation when the turbine load is changing. The obtained results prove the special design of the valve to maintain linear characteristics of flow with stroke position in GCV. The results of the mass flow are given for various GCV stroke openings at various valve pressure ratios. Also, the range of pressure ratios for a proper operation of GCV is determined. SRV regulates the middle pressure between the two parts based on rotor speed. Therefore, a sensitive combination of globes position takes place during gas turbine operation.

Background & Objectives: Mitral valve prolapse (MVP) syndrome is one of the most prevalent abnormalities of mitral valve that arises from pathologic changes of the various parts of mitral valve. MVP may lead to ECG changes, like T wave inversion in inferior leads and atrial and ventricular arrhythmias, in some people that may be misdiagnosed as myocardial ischemia.Methods: This was an analytical (case-Control) study in 50 cases with MVP with age below 30 years who had referred to the Ardabil Bouali Hospital and some private cardiology clinics.The diagnosis of MVP was based on clinical and echocardiographic findings, and after taking history and physical examination, an ECG and an echocardiogram were taken from each person in case and Control groups and the acquired information was analyzed via statistical methods of SPSS software.Results: From 50 studied cases with MVP, 60% (30 cases) were female and 40% (20 cases) were male, and the most commonage range was 21 - 25 years. From these cases, 68%(34 persons) had changes in their ECGs while %32 (16 subjects) did not. In Control group, from 50 persons, 44% (22 persons) had ECG changes and 56% (28 persons) did not.Conclusion: In general this study showed that increase in ECG changes in MVP group in comparison with Control group (p=0.01). In cases with MVP, there was not significant relationship between gender and ECG changes. In comparing case and Control groups, there was not significant difference in ECG changes in females, while there was a significant difference in males (14 of 20 versus 6 of 20) with considering that ECG changes in persons with MVP may be misdiagnosed as ischemic heart disease it is recommended that cases (especially men) with MVP always keep a record of their ECGs.

A common method for Controlling a group of parallel converters in decentralized Control strategy structure in an island microgrid, the use is the droop-down characteristics of frequency ω-P and voltage E-Q. However, the problem with using this method is that the reactive power is not properly distributed (in proportion to the capacity of the micronutrients) between the micronutrients, which may lead to overload in the converters. Microgrids may also suffer from dynamic stability problems such as power fluctuations, which can be increased by switching between active and reactive power Control. To avoid this problem, the X / R ratio of transmission lines is an important parameter that should be carefully considered in the design of micronutrient Controllers. By linearizing and simplifying conditions, the Control system conversion function model becomes a single input-single output system, which is efficient enough to show the relationship between Control parameters such as slope of droop characteristics and derivative sentences, virtual impedance, and voltage Controllers. Using this model, stability conditions for different parameters are analyzed. Also, to improve power distribution stability, common droop strategies are modified by adjusting the slope as well as adding nonlinear sentence sections. This approach reduces the coupling between active and reactive power Control and reduces the dependence of power distribution on grid parameters such as the X / R ratio. To evaluate the reliability of the proposed model, the simulation results in a sample island microgrid in MATLAB software are presented.

When a natural gas pipeline ruptures, the adjacent automatic line Control valves (ALCVs) should close quickly to prevent leakage or explosion. The differential pressure set point (DPS) at each valve location is the main criteria for value setting in ALCV action. If the DPS is not properly adjusted, the ALCV may mistakenly close or it may not take any action at proper time. This study focused on the DPS values prediction for setting ALCV installed on a gas pipeline with 1mm orifice diameter. The effect of characteristic parameters such as pipeline operational pressure (POP) and pipeline pressure drop rate (ROD) due to rupture or major leak was experimentally investigated on DPS. Twenty-five different conditions with double set of typical mentioned characteristic parameters were chosen. For each condition, the differential pressure (DP) was measured over 180 seconds by analyzing the experimental values. Therefore, 25 maximum DP values (DPSs) were obtained. The DPS increases by increase in ROD or decreasing POP parameters. Because of using nitrogen gas instead of natural gas due to safety reasons, the DPS results can be practically applied by adding a safety factor of 15%. The diagram of DPS with respect to ROD and non-dimensional DPS (DOP) versus non-dimensional ROD (RTP) was provided for different POPs.