SpudFiles

im new to this forum and to building potato guns as well...i first built a very small one with a handheld bike pump, a 20 oz pop bottle, and a paintball barrel...i used a garden hose shut off valve form my "trigger"...i have recently decided to go much bigger...im rebuilding my larger cannon today...it will have a 2 foot by 3 inch compression chamber and a 2 inch round barrel...but how long should my barrel be for maximum distance and of course power? it will be ball valve operated because i dont have enough money at the time to make it anything else...my next cannon will be pitsotn operated though

I'd save the money, ball valve cannons work but they're nothing great, and if you're confident enough already to go piston valve, i'd just save for that.

Make sure you read this too:
http://www.spudfiles.com/spud_wiki/inde ... _Rated_PVC

To answer your original question, go as long as you can afford or think best suits you. Because you're using a ball valve, your barrel could be 20' long and you'd still increase performance.

so your telling me that no matter how long my barrel is it will still shoot the same? or are you telling me the longer it is the better it will shoot? and thank you for the link...but i know all about that...i have read up on this before constructing...all of my parts are SCH 40...and i have a few SCH 80 as well

The ball valve opens slow, so a longer barrel helps acceleration.

Sch 40 doesn't mean it is pressure rated, read my article. You may think you know it but it appears otherwise.

If you've learnt how to identify pressure rated pipe and fittings of other websites, I wouldn't trust them. They talk a lot of crap and are usually wrong.

I'm saying you could have an extremely long barrel and it will increase performance because of the slow opening of a ball valve.

But i'd recommend just going sprinkler, or if you're up to it, piston.

all of my stuff IS pressure rated...i am aware of how to identify it and like i said it is all sch 40...i know that does it mean it is pressure rated but im almost certain that the fact all of my fittings say XXX PSI on the side of them mean that they are indeed pressure rated

Okay... I've never seen fittings that say the PSI on the side, but sure.

So you still going ball valve?

for the money go sprinkler....I was amazed at the power difference...

Then again it your just in it for the build then go ball and save the sprink for the next one...

I would go 1.5:1 or 2:1 I use a measuring cup and water it is alot easier than all that math.

i didnt mean my fittings...sorry about that...all of my pipes are XXX psi...my fittings are just identifiably preassure rated

your fittings should say...... nsf-pw

Or NSF-61.

Uhh yeah, i think he knows about PR stuff. Anyway, download GGDT if you want to know how long your barrel should be.
I reckon you should go for the Piston Valve straight away, if your making a gun that big you would be almost wasting all that energy with a ball valve.

I agree with Hydra, you have the knowledge and confidence to go Piston, just do it