Flow calculation through a valve

Hello all. I'm looking solve a problem with a pressure reducing valve where I'm trying to find the outlet flow from a pressure drop. My medium is diesel at 20 deg C, which I've read needs to be factored in from the Kv which is a value given for water between 5 and 40 deg C.

Inlet:
12m^3/h
40 bar

Outlet:
______m^3/h
1 bar

The valve has a Kv value of 3 or another one has a Kv of 15 for example. Which one do I choose and why? From what I've gathered so far, the Kv of 3 means 3m^3/h can pass per 1 bar pressure drop. So 39 bar pressure drop is 3 * 39 = 117m^3/h flow rate?

I believe that the formulas is:

GPM = C[SUB]v[/SUB] [ (p[SUB]1[/SUB] - p[SUB]2[/SUB]) / G ][SUP]1/2[/SUP]

Where:

C[SUB]v [/SUB]= GPM that will pass through valve with pressure drop = 1 psi
G = specific gravity of the fluid,
p[SUB]1[/SUB] = start pressure
p[SUB]2[/SUB] = end pressure