Cv is the rated flow coefficient, defined as the valve open to the maximum, the pressure difference in both sides of the 1PSI valve, 60 degrees of water per minute through several flow control valve, in gallons per minute meter.
The definition of KV is the same, but the unit is not the same, 1BAR differential pressure, flow of water per hour to dress number.
The conversion is. CV=1.167*KV
Cv determines the valve flow capacity, through the formula can take CV numerical calculation process parameters on your site to the standard, so as to control the rated CV valve selection.