This article comparatively analyzes the three kinds of diagnosis methods of cavitation damage of control valves. It is suggested to make full use of the law and control the outlet flow rate to avoid or reduce the damage degree of the valve when selecting the valve. Control valves play a significant role in the fluid industry. Nowadays, with the gradual increase of requirements for energy saving and emission reduction, higher efficiency, continuous and stable operation, fewer spare parts for control valves and quick response to after-sales service, users pay more and more attention to how to optimize, select and use control valves. This is because the control valve acts as an actuator in the device and directly determines the operating status of the device. According to statistics, due to the control valve failure caused by the device as much as 65% of parking, control valve selection of the quality of its products also determine the quality and yield. Review of the past five years, the rapid development of control valve technology, some of the world's leading control valve manufacturers have introduced the valve in special circumstances, such as high temperature, high pressure, cavitation, flash, part of the abrasive medium, high noise Working conditions; the same time, intelligent diagnostic positioner one after another come true, through the positioner can be a good real-time detection of the valve to provide maintenance alarm information to optimize the use of the valve. Needless to say, the improvement of the above technologies greatly guarantees the stable operation of the device and reduces many weak links. But how can we calculate and choose the right valve? According to experience, we can see in the harsh conditions, cavitation often cause damage to the valve parts, accompanied by high noise, internal vibration, blocking flow and so on, the valve calculation and selection, how to reduce and avoid cavitation The occurrence is crucial. At present, valve manufacturers have different evaluation methods of cavitation. In this paper, KE method, δ method and XFz method are mainly used to analyze how to reduce and avoid cavitation and correct valve selection. Control valve cavitation control valve Cavitation phenomenon refers to the media flow through the valve chamber systolic Department, the maximum flow rate, the pressure can be the lowest, if the pressure is lower than the saturation vapor pressure of the medium, the liquid gasification, part of the transformation into Steam or gas bubbles; when the medium flows through the shrinkage Department, the pressure rises, if the saturated vapor pressure exceeds the value, the bubble rupture, re-gas (vapor) into liquid phase, the process is called cavitation or Cavitation (Figure 1). When the bubble burst, the jet release of huge energy and vibration wave, the experiment proved that the bubble diameter of 150μm rupture, the droplet jet velocity of 400km / h, resulting in an instantaneous burst pressure up to several thousand kilograms, the valve Pieces of the surface cause severe impact and erosion wear (Figure 2), but also lead to severe vibration and high noise, blocking the flow of occurrence. Severe cavitation, in a very short period of time, the trim will be damaged or the valve operating characteristics will change. Valve scholar experimentally conducted experiments with water from the microscopic point of view proved the above cavitation process using a mathematical model in which the bubble pressure balance equation is: Pg + Pv = 2α / R + PR is the equivalent radius of bubble, α is the conversion constant, 2α / R on behalf of the bubble surface tension component, Pg is the steam or gas pressure in the bubble, Pv is the saturated vapor pressure of the medium, P represents the ambient pressure where the bubble is located. Pg and R are variables of gas, steam content and bubble volume in the bubble. The introduction of these parameters shows that when the medium flow state changes from stable to flow through the contraction of the lumen of the valve to turbulence instability State, the change of the surface tension of the molecules or droplets of the medium tends to decrease by an order of magnitude when the fluid changes from steady state to unstable turbulent flow state. R represents the process of volume expansion of the bubble before rupture. It is easy to see from the microscopic formula that under certain temperature and pressure conditions, the external pressure inside the bubble and the saturated vapor pressure of the medium are the main parameters that cause the bubble to burst and produce cavitation.
Machinery Parts
Machinery parts is namely machine parts, it is basic components of machine.
Since the present of machine, the corresponding mechanical parts appear. But as also be a discipline, machinery parts separated from the mechanical structure and mechanics. With the development of mechanical industry, new design theory and method, new materials, new technology all appear one after another, then machinery parts entered a new stage of development. Theories such as finite element method and fracture mechanics, elastic hydrodynamic pressure lubrication, optimization design, reliability design, computer aided design (CAD), entity modeling (Pro, Ug, Solidworks, etc.), system analysis and design methodology has been gradually used in the research and design of machinery parts. Better combination of a variety of disciplines, combination of macro and micro to search new principle and structure, more dynamic and precise design, more efficient use of the electronic computer, the further development of design theory and method, is the important trend in the development of the discipline.
Machinery Parts,Aluminum Die Casting Machinery Parts,High Precision Machinery Parts,Machine Part
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