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When selecting valves, attention is paid to two parameters: the flow coefficient and the cavitation coefficient. These parameters are crucial for valves, and information regarding them is generally provided in the data sheets for valves used in advanced industrial production; it is even printed on the sample sheets themselves. There is basically no such information available for the valves produced in our country, as obtaining such data requires conducting experiments; this is one of the key indicators of the gap between our country’s valves and those at the world’s advanced level. ? 3.1, Flow coefficient of the valve? The flow coefficient of a valve is an indicator of its ability to allow fluid to pass through it; the higher this coefficient, the less pressure loss there is when the fluid flows through the valve. ? Calculated using the KV formula, where: KV – flow coefficient; Q – volumetric flow rate in m3/h; ΔP – pressure loss of the valve in bar; P – fluid density in kg/m3. 3.2、Cavitation coefficient of the valve: The cavitation coefficient δ is used to determine which type of valve structure should be chosen for controlling flow. In the formula: H1 is the pressure behind the valve (at the outlet), in m?; H2 is the difference between atmospheric pressure and the saturated vapor pressure corresponding to that temperature, also in m?; ΔP is the pressure difference before and after the valve, in m?. Due to their different structures, various valves have different allowable cavitation coefficients δ. As shown in the figure. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, it indicates that it is suitable and cavitation will not occur. If the cavitation allowance coefficient for the butterfly valve is 2.5, then: If δ > 2.5, cavitation will not occur. ? When 2.5＞δ＞1.5, mild cavitation occurs. ? Vibration occurs when δ<1.5. ? Continuing to use it when δ<0.5 will damage the valve and downstream piping. The basic characteristic curves and operating characteristic curves of a valve do not show when cavitation occurs in the valve, nor can they indicate at which point the operational limits are reached. It becomes clear through the above calculations. Cavitation occurs because, as the liquid flows more rapidly and passes through a converging section, part of the liquid vaporizes, forming bubbles that subsequently burst in the wider section downstream of the valve. This phenomenon manifests in three ways: (1) noise generation; (2) vibration (which, in severe cases, can cause damage to the foundation and related structures, leading to fatigue fractures); (3) damage to the materials (erosion of the valve body and pipes). It is clear from the calculations above that cavitation is closely related to the pressure H1 downstream of the valve – increasing H1 will obviously change the situation. Methods to address this issue include: a. Installing the valve at a lower point in the pipeline. b. Install an orifice plate in the pipeline behind the valve to increase resistance. ? c. The valve outlet is open, leading directly to the reservoir and increasing the space for bubbles to burst, thereby reducing cavitation. ? Based on the analysis and discussion of the above four aspects, a summary is provided showing the main features and parameter lists of gate valves and butterfly valves to facilitate selection. Two important parameters in valve operation.