Different metering valves change the system's "coefficient of flow" which changes the pressure in the system. The fuel has inertia as it moves through the system and as it changes direction, things get weird. Other things besides the valve affect this, but that's the biggest factor. Running the same system and changing the metering valve type will change the pressure.
When doing the math, we use a pressure correction factor get the pressure to calculate out to actual measured numbers. When you see the same numbers pop up for the different valves over and over again, system after system, it becomes apparent what those numbers should be. So, to have the online calculator be as accurate as possible, I built in those different valve types as a menu item and associated them with a number that is used in the calculations.
Spud
