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Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: carl2.0 » Sat Nov 17, 2007 1:43 am

Im a noob to this thing and after alot of research Ive started building my own pneumatic.

My question is
How do I work out my FPS (thats frames per second right ?) for my pneumatic. I dont have a velocity currenty to calculate using equations im seeing online

Im building a

breech loading single shot pnuematic
caliber of 19mm
1.5x 12.5 inch air chamber
28 inch barrel

Any help would be greatly appriciated
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Unread postAuthor: Eddbot » Sat Nov 17, 2007 2:01 am

FPS stands for feet per second, it's a measure of projectile velocity
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Unread postAuthor: Killjoy » Sat Nov 17, 2007 2:25 am

Look in the Wiki for GGDT, it is designed for this kind of stuff among other things. All you gotta do is download it, put in your specs, and it spit out a pretty close estimate of what your velocity will be.
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Unread postAuthor: chaos » Sat Nov 17, 2007 2:31 am

this is what i modeled your proposed gun to be given the data you supplied,

ammo: marbles (4.5g)

pressure: 100psi

Velocity: 486ft/s (Feet Per Second)
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Unread postAuthor: jrrdw » Sat Nov 17, 2007 6:24 am

Chaos, that ganaric valve would be the sprinkler valve correct? Is that what your going to use carl2.0?
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Unread postAuthor: carl2.0 » Sat Nov 17, 2007 1:37 pm

Oh i just have a blow gun valve ...the air chamber on the input and the barrel on the output

I figured it was a more simple cost effective valve solution( 3/4 inch sprinkler valve is like $40 here while the blow gun valve is just $10)
But what is the advantage of using the sprinkler valve triggered by the blow gun valve over just the blow gun valve ??
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Unread postAuthor: Ragnarok » Sat Nov 17, 2007 1:56 pm

@chaos: You left the dwell time at 0. That normally needs to be kept high, 1000 or so.
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Unread postAuthor: frankrede » Sat Nov 17, 2007 1:58 pm

carl2.0 wrote:Oh i just have a blow gun valve ...the air chamber on the input and the barrel on the output

I figured it was a more simple cost effective valve solution( 3/4 inch sprinkler valve is like $40 here while the blow gun valve is just $10)
But what is the advantage of using the sprinkler valve triggered by the blow gun valve over just the blow gun valve ??

Indeed. You just saved 30$!
And now you have a cannon that has crap performance.
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Unread postAuthor: benstern » Sat Nov 17, 2007 1:59 pm

A blowgun valve won't do squat. You need a larger valve.
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Unread postAuthor: jrrdw » Sat Nov 17, 2007 3:15 pm

The blow gun will not give you no where near enough flow, the marble is just going to roll out of the barrel and fall to the ground probly. The idea behind useing the sprinkler valve is to release all the stored air at once. That way your cannon will shoot the marble with a good amount of power. The sprinkler valve will be worth the investment.
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Unread postAuthor: Fnord » Sat Nov 17, 2007 3:25 pm

The marble won't "roll out the barrel" with a blowgun, but it won't be anywhere near what you'd get with a sprinkler. You'll probably get a couple hundred fps with a blowgun, but I wouldn't be too happy with that.

Edit: I tried it before, I know. Flow was cut down to a hole .17" diameter, but I could still launch light ammo fairly fast.
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Unread postAuthor: chaos » Sat Nov 17, 2007 3:44 pm

Ragnarok wrote:@chaos: You left the dwell time at 0. That normally needs to be kept high, 1000 or so.


yer sorry i've never really modeled a gun with a sprinkler valve, not that it matters now.

dude a blowgun will be a crap choice if you intend on larger bore size.
i would only use a blowgun as a valve with a small caliber barrel bore, otherwise the gun will suck the big one.
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Unread postAuthor: psycix » Sat Nov 17, 2007 3:49 pm

You got 2 types of valves: valves and valves.

Yours is a valve, a sprinkler is a valve

Now the valve gives flow and your valve gives flow.
Its all about the flow, and since flow = power, your valve is the most important thing on your gun.

Moral of the story:
Bigger valves give more power.
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Unread postAuthor: MrCrowley » Sat Nov 17, 2007 4:09 pm

Even a 1/4" ball valve will be better then a blow gun.

With a blow gun, shooting a marble, the marble will go about 10meters.

Since a sprinkler valve cost you $40, you probably don't live in America.
If you live in Aussie they cost about $15 at bunnings, if you live in NZ they cost about $40, if you live in Europe I don't know the cost.

Anyway, get a sprinkler valve, you wont regret it.
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Unread postAuthor: MaxuS » Sat Nov 17, 2007 6:21 pm

Theyre around $50 if you live in europe, for just a 1 incher.
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