SpudFiles

I just got a 5' length of 2.5" sch40 PVC from mcmaster for my new tennis ball cannon.

I was shocked at how tight of a fit tennis balls are. Is this a good thing or a bad thing? I almost feel like redesigning my gun for breech loading because they are so damn hard to shove down the barrel.

Its a good thing, you dont want them to roll down the barrel, when you release the air from the chamber onto the backside of the tennis ball, they compress and then bounce back giving you more product for your money if you see what i mean...They help themselves to travel further.
Also, if they werent a tight fit, they wouldnt compress as much and not as much pressure would gather behind them before they made it out of the barrel, so yeah, tight fit = good thing.

Any suggestions on chamber vs. barrel length in a gun using a 2.5" barrel, 3" chamber, and a 2" sprinkler valve?

I want to build this gun as compact as I can. < 5 feet

3ft x 3" chamber
4ft x 2.5" barrel

That should do it, but i would increase the barrel length to 5ft with a 3ft chamber, you will get a lot more range with a tennis ball that way, when using a 2" sprinkler valve... you want to go big!

I hope that you realize how incredibly expensive 2" sprinkler valves are... it almost blew my mind out lol.

Theyre rather affordable if you want one, you shouldnt even be thinking about buying a 2" sprinkler valve if you are not serious about power.

If you are serious about power, your money is much better spent on a piston valve.

Why build a piston valve when I can get a commercial valve for under $50?

...Point proven..
Besides, if you're not very confident in piston building, or can't get one to seal properly, then theres only one other route.

PVC Arsenal 17 wrote:Why build a piston valve when I can get a commercial valve for under $50?

Because piston valves perform much better than commercial sprinkler valves.

It is the same reason people will spend thousands of dollars on engine modifications to increase the performance of their cars. Some people jut want more power, and are willing to pay and work for it. Hell, for some people the work itself is a reward along with the power increase.

Theres nothing like when the piston valve works the first time, i allmost creamed my jeans! And it don't stop there, it's every shot!!! Thats why every pneumatic user should build a piston valve. It's next to sex.

I was looking at diagrams of the valve I got, and it actually appears to open nearly as much as a 2" ported piston would. (1/2")

Power is fine, but when I can get a sprinkler for cheaper than just the parts needed to build a piston, I'll take the sprinkler. Besides, I've been looking at videos of a gun with a smaller ported sprinkler than mine and the results are impressive.

I've attempted pistons before, but I'm severely limited to what I can do since I don't have a lathe. When I try to improvise, I always end up getting unreliability and problems. Of course I can chop off my left testicle to afford one of Gort's valves, but when a dirt cheap deal on the next best thing comes my way, I'll take it.

Just out of question is there a size difference between 2.5 inch pipe from McMaster, and 2.5 inch Sch 40 electrical conduit from Lowes.

I know there is a pressure rating difference, but it's a barrel and I don't care about pressure. I just know that conduit is a ton cheaper than regular white PVC and I was wondering what the difference is.

The grey conduit paints just as well and is sunlight resistant. What is the downside?

As far as I know, there shouldn't be. Just bring a tennis ball to Lowes and check. That's what matters.

Buying parts for a 2 inch piston valve will not cost mire thean your sprinkler valve, heck my last 2" valve cost me 10 bucks to make.