I'm currently doing pump sizing calculation, so I have to determine the total pressure loss of my piping system. Most of commercial components like ball valve, check valves, strainers, etc. have experimental data from suppliers indicating the flow coefficient (Cv) for water at 60degF. If I want to calculate the resulting pressure loss, I get it from following formula:

deltaP (psi) = GPM^2 * Specific Gravity / Cv^2

My problem is that the fluid in my system is oil. How to evaluate the Cv factor for other fluid than water? I assume it should depend at least on fluid viscosity?

If it is not possible to determine the Cv factor for other fluids without practical experimention, how to determine the pressure loss through the valves and other components?

Viscosity does have an effect on flow.  However, for fully turbulent flow, the effect is very minor.  Check out the the Moody friction factor chart.  For high Reynolds numbers, the friction factor is essentially a flat line. In these cases, only the fluid density is needed to calculate the pressure drop given the resistance (k), or the equivalent feet.

If the flow is not turbulent, all bets are off.  Even your equation above may not work well for water.

This is a good question. As valves represent a minor loss we should extend the considerations above to other items which represent minor losses too.

The minor loss can be converted to a length equivalent to the length of a pipe that would produce the same pressure loss.
Head loss can be expressed as:
dp =