The types of valve I can see of use are:
- Ball valve
- Sprinkler valve
- Quick exhaust valve
- Slide valve
- Piston valve
Spud-gunners tend to use a QEV as they open really quickly, but I don't know what too quick is for a WB. If the valve opens too quick won't the WB burst in the barrel, or does that depend on the quality of the sabot?
The slide valve is a kind of wild-card. I haven't seen anyone use a slide valve for any launcher.
The QEV is the cheapest valve (other than a ball valve) for me, but only goes up to 3/4" bsp (but that has greater flow than a 1" bsp sprinkler valve, apparently).
EDIT:
I've found a 1" bsp QEV aswell.