Fluid dymanics basics ball valve full open vs. half open

[Mick McCormick]

is there any difference and why ? I have a ball valve with 100 psi jet fuel on one side and atmosphere on the other end ? Is there any difference if o have 100 psi and the valve all the way open vs. say 200 psi and only half way open . Please explain ?

 

[Rx7man]

I think there will be a significant difference... for starters, a half-open ball valve has 2 restrictive points (each side of the ball), and depending on the ratio of the size of the ball compared to the size of the hole through it, half-open may only be 30% of the area... This will also introduce a LOT of turbulence

 

[JBA]

I just realized I still have an old Excel calculation I developed to determine to of flow area vs ball valve opening angle; and, taking a quick look at he graph curve of that calculation shows that at 1/2 (45°) open the flow area on each ball end is 39% of the full open area of a full bore ball valve. In addition, there will also be the extreme turbulence issue stated by Rx7man.