Regulator valve selection issues (Cv value use)
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This post was last written by doubly_Fly edited on 2022-12-21 16:24 Hi friends: I have an instrument data sheet for regulating valve (flow), which is used to purchase regulating valves. On the table: calculated Cv=13.4, rated Cv=68, regulating valve inlet and outlet connection diameter 2'' (pipeline 3''). Question: According to common sense, the rated Cv value is determined based on the calculated Cv value. The rated Cv value is approximately 1.5~2.0 times to calculate the Cv. Then, according to the equipment manufacturer's control valve characteristics, the rated Cv value determines the caliber of the control valve. However, in this data sheet, although the control valve equipment manufacturer did not provide investment information, the caliber of the control valve has been determined (2''), and the rated Cv value is also determined (68), and is more than 5 times higher than the calculated Cv value. Is this normal? (Currently, professional piping drawings have been delivered)
. This situation is not common, but it happens. This situation often occurs when the transmission capacity of the pipeline where the regulating valve is located is close to the limit (even if the pipeline is not equipped with a valve, the flow rate is not much greater than the maximum flow calculated by the regulating valve), and the allowable front and rear pressures left for the regulating valve are almost the same. ； Furthermore, this set of drawings may have been transplanted, and a large Vc value was chosen based on past experience. .
According to you, is this a remedial measure because the pump selection is too small, or the pipeline is too thin?
. This is possible, and the specific process parameters must be calculated and confirmed. This is also the experience I gained from participating in the capacity expansion and transformation of imported equipment several times. The feed pipeline designed by foreigners is simply a constant throttling pipe. When the flow rate reaches a certain value, it cannot increase, so it has to be replaced with a larger pipe.