Hi, I want to use a 2/3way valve to fill and then fire my qev based launcher, do I need a normally open or closed 2/3way valve?

Many thanks Ian

A bit of background I have been using a Parker 3/4" valve at 400psi max (bit scary) but now want to built one using a Humphreyas heard many positive opions and even seen a page where a guy modified his (spring/hole) to fill the chamber but I dont want to do this to my new qev. I have been using 12mm...