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The role of valve flow coefficient and cavitation coefficient in valve operation

by:Sino Valves     2021-03-11
The important parameters of the valve are the valve's flow coefficient and cavitation coefficient, which are generally available in the valve materials produced in advanced industrial countries, and even printed in the samples. The valves produced in our country basically do not have this information, because obtaining this information requires experiments to be put forward. This is one of the important manifestations of the gap between my country and the world's advanced level of valves.     One, the flow coefficient of the valve      The flow coefficient of the valve is an index that measures the flow capacity of the valve. The larger 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     2. The cavitation coefficient of the valve is selected by the value of cavitation coefficient δ What kind of valve structure to choose when controlling flow.     where: H1-valve (outlet) pressure mH2-atmospheric pressure and its temperature corresponding to the saturated vapor pressure difference mΔP-the pressure difference before and after the valve m                 various valves due to different structures, 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, it means it is available and cavitation will not occur. If the allowable cavitation coefficient of the butterfly valve is 2.5, then:      If δu003e2.5, cavitation will not occur.     When 2.5u003eδu003e1.5, slight cavitation will occur. When       δu003c1.5, vibration occurs. If     δu003c0.5 continues to be used, the valve and downstream piping will be damaged.    The basic characteristic curve and operating characteristic curve of the valve cannot tell when cavitation occurs in the valve, let alone reach the operating limit at that point. Through the above calculation, it is clear at a glance. Therefore, cavitation occurs because when the liquid passes through a tapered section during the accelerated flow process, part of the liquid vaporizes, and the generated bubbles subsequently burst on the open section behind the valve. There are three manifestations:      (1) noise (2) vibration (severe) (3) Damage to materials (corrosion to the valve body and pipeline)      From the above calculations, it is not difficult to see that cavitation has a great relationship with the post-valve pressure H1. , Increasing H1 will obviously change the situation, improvement 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 resistance.    C. The valve outlet is open, and the reservoir is directly stored, which increases the space for bubble bursting and reduces cavitation.     Synthesize the above-mentioned analysis and discussion, sum up the main characteristics and parameter list of gate valves and butterfly valves to facilitate selection. Two important parameters play a pivotal role in the use of valves.
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