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Detailed flow coefficient and cavitation coefficient of the valve
The important parameters of the valve are the flow coefficient and cavitation coefficient of the valve, which are generally available in the valve data produced in advanced industrial countries, and even printed in the sample. There is basically no such information in the valves produced in China, because obtaining this information requires experimentation, which is one of the important performances of the valve gap between China and the world. First, the flow coefficient of the valve The flow coefficient of the valve is an indicator to measure the flow capacity of the valve. The larger the flow coefficient value, the smaller the pressure loss when the fluid flows through the valve. Calculate according to the KV value: KV—flow coefficient Q—volume flow rate m3/hΔP—pressure loss of the valve barP—fluid density kg/m3 II. The cavitation coefficient of the valve is selected by the cavitation coefficient δ value. What kind of valve structure type to choose when controlling flow. In the formula: H1—post-valve (outlet) pressure mH2—the difference between the atmospheric pressure and the saturated vapor pressure corresponding to its temperature. mΔP—pressure difference before and after the valve m. Because of the different configurations of various valves, the allowable cavitation coefficient δ is also different. as the picture shows. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, it means that it is available and no cavitation will occur. If the butterfly valve allows a cavitation coefficient of 2.5, then: If δ > 2.5, no cavitation will occur. When 2.5>δ>1.5, slight cavitation occurs. When δ < 1.5, vibration is generated. When the condition of δ < 0.5 continues to be used, the valve and the downstream piping are damaged. The basic characteristic curve and operating characteristic curve of the valve are invisible to the time when the valve is cavitation, and it is impossible to reach the operating limit at that point. Through the above calculations, it is clear at a glance. Therefore, cavitation occurs because some liquid vaporizes when a liquid passes through a tapered section during accelerated flow. The resulting bubbles then burst in the open section behind the valve. There are three manifestations: (1) noise occurs (2) vibration (serious It can cause damage to the foundation and related structures, resulting in fatigue fracture. (3) Damage to the material (erosion of the valve body and the pipeline) From the above calculations, it is easy to see that the cavitation and the post-valve pressure H1 have a great relationship. Increasing H1 will obviously change the situation and improve the method: a. Install the valve at the lower point of the pipeline. b. Install an orifice plate on the pipe behind the valve to increase the resistance. c. The valve outlet is open, and the direct reservoir is used to increase the space for bubble bursting and reduce cavitation. Based on the analysis and discussion of the above four aspects, it is easy to select the main features and parameter lists of gate valves and butterfly valves. Two important parameters play a decisive role in valve operation.