Help troubleshooting - tennis ball attachment not working

[Guaps]

I made this exact piston valve (MrRedRooster)
http://www.youtube.com/watch?v=2bvXiswEDSo
I put an adapter on there so it has a removable barrel, and removable canister. I made a 3/4" marble/acorn barrel that works beautifully with a 1L metal cylinder. Then I made a 2"x36" PVC canister for a 2.5" x 60" tennis ball barrel. When I put 100 psi in it, the tennis ball barely comes out of the barrel. It flies maybe 10 yards.
I used GGDT to try and figure out what I'm doing wrong, but it is asking for a lot of info I'm just guessing at. I estimated friction at 12psi per some other thread I found here, put in all the other values and it says a 6" barrel is optimal. Something is wrong. Any ideas? What info should I post here?
Thanks!

[Fnord]

Your valve is restricting flow. You really should have a valve that is 50% or more of the barrel diameter. 75% and up works great.

Also, your chamber : barrel ratio is on the low side; around 0.3:1.

At some point adding more barrel length will decrease power, which may also be happening here. A ratio of 1:1 is fairly common, though not super-efficient for 100psi.

[Guaps]

Thanks - I guess this just isn't going to be shooting tennis balls if the valve is the main problem.

Like I said in my original post, GGDT said my barrel was too long, but I thought maybe that had something to do with my guesstimates.

How did you calc that chamber:barrel ratio?

[jackssmirkingrevenge]

How did you calc that chamber:barrel ratio?

2"x36" chamber -> 113 cubic inches

2.5"x60" barrel -> 295 cubic inches

So around 0.38:1, as Fnord pointed out, that kind of ratio coupled with your limited valve flow vis a vis the barrel diameter is not going to make for good performance.

One thing to get around poor valve flow/opening time is to use a detent or burst disk, here's something I proposed recently elsewhere:

[Guaps]

I'm brand new to all of this - I saw the video on how to make a piston valve and decided I needed to try it. And it was tons of fun. That said, I'm totally lost looking at your diagram. I need to go do some reading about detent and burst disks. Looks like another fun project. Thanks!

[Technician1002]

The rate of flow into the large diameter tennis ball barrel is more important than just a large chamber. I tested a similar small chamber/large barrel setup going to an extreme. The valve is much larger with the minimum diameter orifice between the chamber and barrel of 1 inch.

Here is the launcher;


The ability to flow enough air in a short time is very important. Use a large valve on a large barrel.

And here is the performance at about 110 PSI;
[youtube][/youtube]

A larger valve with a larger chamber on the same barrel has some serious raw power.
3gallon chamber and a 2 inch porting valve;
[youtube][/youtube]