When I was running the red outfit special, I fitted a Conways anti sumping valve. There is an arrow upon the case where the Vee of the arrow depicts the direction of travel of the oil, or, if you like, the direction that the valve is to be fitted. I enlarged the bleed hole in the brass body, tapped it M6 and made a threaded tube four inches long to screw into the tapping. Onto this I fitted a small funnel so that I could fill it with oil and let gravity fill the oil line below the valve, thus priming the system. I never had any problems with the device. The hole was sealed with an M6 pan head s/s set screw and obligatory red fibre washer. I would not trust my memory if a ball valve was fitted, unless it could be fitted with a system where the ball valve had to be turned on to activate the ignition. Cheers, ET43