Valves important parameters are the valve flow coefficient and cavitation coefficient, which in the advanced industrial countries generally available in the valve information, and even printed in the sample also. 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. First, the flow coefficient of the valve The flow coefficient of the valve is a measure of the ability of the valve flow index, the greater the value of the flow coefficient, the smaller the pressure loss when the fluid flows through the valve. According to KV value calculation formula: KV-flow coefficient Q-volume flow m3 / hΔP-valve pressure loss barP- fluid density kg / m3 Second, the cavitation coefficient of the valve cavitation coefficient δ value to select For control of flow, choose what kind of valve structure type. Where: H1 - the pressure after the valve (outlet) mH2 - the difference between the atmospheric pressure and the saturated vapor pressure corresponding to its temperature mΔP - the pressure difference before and after the valve m due to different structures of various valves, so the allowable cavitation 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 cavitation will not occur. If the butterfly valve allows cavitation coefficient of 2.5, then: If δ> 2.5, then 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 part of the liquid is vaporized when a liquid passes through a gradually decreasing cross-section during the accelerated flow. The resulting bubble then opens up a broad-area burst after the valve. There are three manifestations: (1) noise occurs (2) vibration (3) damage to the material (erosion of the valve body and pipeline) From the above calculation, it is not difficult to see that cavitation and valve pressure H1 have a great relationship , Increase 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. Open the valve outlet, direct reservoir, so that the bubble burst space increases, reduced cavitation. Based on the above four aspects of analysis, discussion, summed up the gate valve, butterfly valve main features and parameter list easy to choose. Two important parameters in the valve used to play a decisive role.