Valve flow coefficient and cavitation coefficient is an important valve parameters, which are generally available in the advanced industrial countries, the valve material, even in the sample also printed. China's production of the valve is basically no information in this area, because access to this information need to do experiments can be made, this is our country and the world's advanced level of the valve one of the important performance gap. 3.1 Flow coefficient of the valve Flow coefficient of the valve is a measure of the flow capacity of the valve. The larger the flow coefficient, the smaller the pressure loss when the fluid flows through the valve. According to KV calculation formula: KV-flow coefficient Q-volume flow m3 / h ΔP-valve pressure loss bar P-fluid density kg / m3 ?? 3.2, the valve cavitation coefficient? Gas Erosion coefficient δ value, to select the control flow, choose what kind of valve structure type. Where: H1 - after the valve (outlet) pressure m? H2 - atmospheric pressure and its temperature corresponding to the difference between the saturated vapor pressure m? ΔP - before and after the valve pressure difference m? Various valves due to different structures, therefore, allowed cavitation The coefficient δ is also different. as the picture shows. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, then it is available and no cavitation will occur. If the butterfly valve allows a cavitation coefficient of 2.5, then: • If δ> 2.5, cavitation does not occur. When 2.5> δ> 1.5, slight cavitation can occur. When δ <1.5, vibration occurs. δ <0.5 continued to use the case, it will damage the valve and downstream piping. The basic characteristics of the valve and operating characteristics of the valve, the valve cavitation occurs at a time when it is out of sight, not to mention that at that point to reach the operating limit. Through the above calculation is clear at a glance. Therefore, cavitation occurs because the liquid accelerates the flow through a section of the tapered section, the part of the liquid gasification, the resulting bubble followed by the valve after the open section burst, the performance of three :? (1) the occurrence of noise (2) vibration (In severe cases, it can cause the destruction of foundation and related structures, resulting in fatigue fracture.) (3) Material damage (erosion of valve body and pipeline) • From the above calculation, it is easy to see that cavitation and post-pressure H1 There is a great relationship, increased H1 will obviously change the situation, to improve the method:? A. The valve installed in the pipeline lower. b. Install the orifice plate on the pipe behind the valve to increase the resistance. c. Valve outlet is open, direct reservoir, so that the bubble burst space increases, reduced cavitation. ? Comprehensive analysis of the above four aspects, discussion, summed up the gate valve, butterfly valve main features and parameter list easy to use. Two important parameters in the valve operation.
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