which is faster

[McThrust]

which is faster, a homemade piston assembly, or a modded sprinkler valve?

[Brian the brain]

a homemade piston actuated by a modded sprinkler valve would do the trick

[McThrust]

but what if it is for quite a small cannon? wouldnt the air rush out the sprinkler valve too quick and therefore stopping flow to the barrel? anyway, what valve is best for a small chamber capacity?

[Shrimphead]

How big of a chamber? A piston or diaphragm is going to outperform a sprinkler valve even in a 1" chamber cannon, but it will make a bigger increase in performance as the chamber gets bigger.