Rufus2k; You probably have your equipment built by now, but a few comments. If you require much accuracy and repeatability you might consider other methods, mainly because of material properties variations. A shear pin would be better, but for best accuracy and repeatability it should be notched...
Assuming you plan to use line size valve. B/F valves have lower pressure drop (Higher Cv)and with constant head will have greater flow rate. Gate valves are generally more rugged. Soft (rubber) seated B/F valves and wedge gate valves will both give bubble-tight shut off. B/F easier and quicker...
