SIZE matters

[no-limit]

What is the largest size barrel can you use with a 2" piston using a 2" T. I was thinking a 1 1/2" barrel unless using an adapter.

[MrCrowley]

You could use a 4" barrel if you wanted to and had the right adapters.

The 'seat' (what the piston seals against) would have to be smaller then 2", but you can use threaded adapters so you can have a larger barrel.

http://www.spudfiles.com/forums/v-a-l-p ... 14702.html

[jrrdw]

Yes but the bigger the barrel the weaker the shot.

[MrCrowley]

Well not necessarily when F=ma. If you maintain a light projectile while increasing the surface area you are going to have more force impact on that projectile, more force = more power in simple terms.

Edit: That's why sabots can give better performance then if you used a small barrel that fit what ever you were 'saboting'.

[SpudUke5]

Yes Mr.Crowley is right for obvious reasons, but you may not get the power and speed you want.

For example, if you shot a marble and the rock (saboted) they both should have the same power. The marble would go slower and the rock would go faster. So in order for them to have the same force, the heavier object need to be slower and the object that weights less should go faster than the heavier object.

But you would have the valve restricting your flow which would make the performance not as good as a bigger valve with the same barrel size.

Food for thought

[no-limit]

So if 1 1/2" is the right size for the seat (don't know how you could make it any bigger), a 1 1/2" barrel would be the best fit?

I seem to be having alot of trouble getting this last piston together. Since I shoot rockets I have thought about using a cross instead of a T, getting air from both sides and being able to make it easier to stand up and add more power. Think that will work?

[Lentamentalisk]

It really depends on the speed you are hoping for. The heavier the projectile, the better it can handle a low flow valve, as it will never get up to too high of a speed anyways.

[jrrdw]

2" piston valve built in a cross.








The Basterd

[Spuddin]

interesting question no-limit because im in a delima myself. i will soon have a 1 inch modded sprinkler valve to go on my mortar but instead of my golfball barrel i want to shoot softballs but i dont think the performace will be all that good and i dont want to build a big piston valve gun either. i want to stay with my original design. 100 psi through a 1" valve into a 4" barrel.
btw jrrdw whats the latest on that cannon?

[no-limit]

Something like I want there jrrdw, except straight up. It looks like a 2" piston with a 2" barrel, in a 2" cross, don't see how that could work. I do think a cross would work better than a T though, seems it would be faster with more volume on the other side, 2 sides better than 1.

So far I have gotten my 1" sprinkler valve to work really good with a smaller (3/4") barrel. A 4" barrel, I doubt it would work, especially at 100 psi.

[MrCrowley]

Something like I want there jrrdw, except straight up. It looks like a 2" piston with a 2" barrel, in a 2" cross, don't see how that could work.

Listen, as long as the SEAT is SMALLER then the TEE you can have ANY size barrel you want. He probably just adapted the 2" barrel down to a small size INSIDE the tee. Use your head, it's really not difficult to understand.

A 4" barrel could work on a 2" piston valve as long as your seat is smaller then 2" (so a 1.5" barrel would be your seat).

If you looked at my cannon I linked you, you would see in the How-To I posted in the topic, that I used 1.5" pipe as my seat but I use a 2" barrel and a 1.5" barrel. The 1.5" seat, is exactly that. Just the seat for the piston to seal against. It has nothing to do with the barrel.

Considering people have used tennis ball barrels with 1" sprinkler valves, using a 4" barrel on a 1.5" seated, 2" barrel sealing piston valve will still work. It's not like when you fire the cannon it will print out an error saying 'your barrel is too big'. It will still launch the projectile. No such thing as 'it wont work'.


Here's my how-to, read it carefully because you've made quite a few piston topics and haven't really gotten that far with them: http://www.instructables.com/id/Golfbal ... That-Shoo/

[no-limit]

"He probably just adapted the 2" barrel down to a small size INSIDE the tee." That is what I figured, "It looks like a 2" piston with a 2" barrel, in a 2" cross, don't see how that could work".

My only mistake was using barrel and seat as the as dia..because I did say in my original post "1 1/2" barrel unless using an adapter." but don't think anyone read that. I just wanted to know the biggest barrel you could use WITHOUT ADAPTERS.

"It's not like when you fire the cannon it will print out an error saying 'your barrel is too big'" No but the GGDT will say it.

Right now I'm trying to make it as perfect as possible. It doesn't seem possible to get that close though because of the inside of the pvc has so many bumps in it making sealing it tough. I keep making mistakes trying to make it perfect.

[MrCrowley]

It may say 'WRN: Barrel unnecessarily long' but that doesn't really matter, it depends on what you are shooting.

I meant that the cannon will still shoot the projectile, making this comment "I doubt it would work" wrong. With a 2" piston valve you could have a 4" barrel 3' long according to GGDT without any errors, you could make it longer and you'd only loose 3fps for an extra 2' in length.

The largest barrel you can have without adapters would be 1.5". But I wouldn't bother making a piston valved cannon without interchangeable barrels. It's also far easier to make a piston valve with interchangeable barrels compared to one without.

You might have to modify some bushings and it would a pain to glue a whole barrel into a tee and it would put stress on the barrel as well.

[jrrdw]

btw jrrdw whats the latest on that cannon?

The chassis frame is built and the cannon is mounted on the pivot. Still debating on the onboard air system. Slow and steady wins the race!

This solvent weld in adapter was placed in my drill press and sanded down to fit snuggly into the 2" outer barrel.

Then I cut off the square nut and welded it in flush, then sanded it down flush to get it square to the 2"pipe.

Then I used sand paper and cleaned out the inner diameter just big enough to house a 1" inner barrel. I don't have a available picture of the 1" inner barrel coming through the customized adapter.



In this picture you can see where the inner barrel meets the piston in the center of the cross. Same as the 1st picture.


The moral of the story is you can modify in all sorts of ways to get what you need. It was very easy to do. PVC sands quick and easy.

[no-limit]

"I meant that the cannon will still shoot the projectile, making this comment "I doubt it would work" wrong." OK then I will modify it accordingly, I doubt it would work as good as a smaller barrel.