Which is larger, the Kv value or the Cv value of a valve?
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According to various sources, the Cv value is greater than the Kv value; generally, Cv = 1.156Kv. However, when I carried out the calculations using formulas, it seemed that the two values were reversed – it should be Kv = 1.156Cv. Did I make a mistake in my calculations, or is the formula I used incorrect?
This post was last edited by hjame on 2019-9-8 08:28. When Kv=1, the corresponding Cv is 1.156; this indicates that under these unit conditions, the conversion factor between Cv and Kv is 1.156, that is, Cv = 1.156Kv. At the same state point, the Cv value is greater than the Kv value.
Which is larger, the Kv value or the Cv value of a valve? In fact, for example: Kv=1 and Cv=1.156 represent the same state. (The definitions of Kv and Cv are based on the International Electrotechnical Standard IEC 60534-1-2005 or the domestic standard GB-T 17213.1-2015 Industrial Process Control Valves – Part 1: Terms and General Principles.) It’s just like asking which is longer, 1 meter or 100 cm For the same unit of length, numerically 100 is certainly larger than 1, but 1 meter is equivalent to 100 centimeters.
Oh, I see now; it seems that the editing quality of that book on MMD isn’t very good either.
Remove Q', remove P' – it’s just a different unit
By definition, Cv is the flow rate at 1 psi; are you calculating that the flow rate is 4.4 gpm at a pressure difference of 14.5 psi?
Isn’t it cv=1.167kv? Could you explain how 1.167 was calculated?
The source of the coefficient 1.167 (some sources indicate 1.17 directly): the pressure unit is kgf/cm2 (a unit commonly used in older documents). The relationship is: 1 bar = 1.0197 kgf/cm2; this value can be used to convert according to the defined formula. Some materials are convenient but imprecise; they do not specify the units corresponding to the coefficients, which can lead to misinterpretation.