What exactly are the conversion factors for Kv and Cv?

Cv=1.156Kv and Cv=1.167Kv – both values exist; which one is used depends on the units adopted and their corresponding values. GB/T 17213.1-2015 Industrial process control valves – Part 1: Terms and general principles for control valves. Standard definition: The flow coefficient Cv is a flow regulation coefficient for control valves that is not part of the International System of Units, but it is widely used worldwide. CV can be expressed numerically as the number of US gallons of water at a temperature of 40 \"F to 100 \"F that flow through the valve in 1 minute, with a pressure drop of 1 psi. The Kv flow coefficient, Kv (m3/h), represents the specific volume flow rate (capacity) through the valve under the following conditions and specified stroke: a static pressure loss across the valve of 10^5 Pa (1 bar, which is equivalent to 100 KPa); the fluid is water at a temperature range of 278 K to 313 K (5°C to 40°C) ； The unit of volumetric flow rate is cubic meters per hour (m^3/h). In this case, the conversion factor is Cv=1.156Kv. If the pressure used in calculating Kv is expressed in kgf/cm^2 (note: square centimeters, a unit commonly used in older documents), then Cv=1.167Kv. The main reason for this difference lies in the need to take the square root of the coefficient g (9.81) when converting between these two units of pressure.

Then I calculated using the formula in the book and got Kv=1.156Cv; I was completely confused

Thank you for your reply. Also, why do I get a value of Kv=1.156Cv when I do the calculations myself? It’s written the same way in the book I’m reading – is there an error in the formula in the book?

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.