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First Pneumatic Launcher

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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First Pneumatic Launcher

Unread postAuthor: blackosprey » Sat Nov 03, 2007 2:31 am

Hey I'm about to build my first pneumatic launcher, and I had a few questions. First topic by the way, although I've posted once or twice.

What I want:

To be able to shoulder it, and have it be rather small. At least smaller than this. I'm not really sure what barrel size I'm looking for, probably about 1/2" sch 40 PVC according to the wiki. I'm planning to use it as both a slug launcher and as a small shotgun.

I want to use CO2 as my air source, whether it's from 12g cartridges or my paintball tank. If anyone knows of a better gas, tell me. It would be pretty cool to have a 12g for each barrel. Oh yes, and multiple barrels :twisted: That is, if I can pull it off.

This is where I'm a little confused. Is it possible to have a valve that releases a fairly consistent amount of gas each time, and on demand instead of when the valve hits a certain psi? I could use a QEV with a blowgun, then hook the air source straight up to the QEV, but that would be very precise. Any help would be great.

Anyway, thanks for your time, I know that was a little long.
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Unread postAuthor: Hubb » Sat Nov 03, 2007 2:51 am

It would be better to have a chamber. If you are concerned about size, make a small metal chamber and put high pressures in it. CO2 tends to run between 800 and 900 psi (depending on the temperature) so it will be a good choice.

As far as a valve to use, the QEV is a good choice, but I wouldn't count on it to hook straight to the CO2 without a regulator. And even with a regulator, it will probably give "less than adequate" performance for what you seek.

The QEV works similar to a sprinkler valve and, once it is opened, it may stay open until the air is run out.
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Unread postAuthor: blackosprey » Sat Nov 03, 2007 3:19 am

That's a lot of psi to be messing around with... I'm wanting to use this as an airsoft shotgun, so 800 psi is way more than idea. Like deadly. I think my opponents would not be happy with that.

That's actually the reason I wanted to use the 12g cartridges, do they run at that psi too?
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Unread postAuthor: jackssmirkingrevenge » Sat Nov 03, 2007 3:23 am

blackosprey wrote:That's actually the reason I wanted to use the 12g cartridges, do they run at that psi too?


Yes... why not hook up one of these to your barrels:

Image

A small burst of CO2 for every press of the trigger.
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Unread postAuthor: Hubb » Sat Nov 03, 2007 3:43 am

CO2 is CO2. All of it runs at the same pressures (providing the temperature is constant). You can hook up a regulator to knock this much PSI down and make it usable.

As far as pressure that a 12g will provide to a chamber, well that all depends on the chamber size.

For any questions you may have concerning CO2, or the pressure of a 12g in a given chamber, check The CO2 FAQs.

Also, I made a CO2 Calculator that may be of interest.
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Unread postAuthor: blackosprey » Sat Nov 03, 2007 12:11 pm

Jack: Is that tire inflater consistent and does it have a fast exhaust time?

Hubb: I think I am liking your idea about having a small metal chamber with high pressures. Is there a way to have the chamber valve release a certain amount of psi into the barrels before closing the valve again, consistently?
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Unread postAuthor: Ragnarok » Sat Nov 03, 2007 12:29 pm

blackosprey wrote:Jack: Is that tire inflater consistent and does it have a fast exhaust time?

No, and no. Neither of those things. Those are inaccurate, and low flow to compensate for that (if they were high flow, there would be many a burst tyre).

I would suggest against multiple barrels. It will either get very complicated or very expensive fast - and more than likely, both.
A breech, bolt action, or perhaps a break open style loader would be easier, cheaper, and still pretty fast.

Also, getting multiple bursts from one chamber is always going to be inconsistent, as pressures drop slowly.
However, if you have a 12g bulb regulated down by some method, then fed through a slide valve trigger, feeding into a QEV, then that would create the effect - each pull of the trigger would create one consistent pulse of air, at least until the 12g went dry.

You'd still need to find a way of getting ammo in front of that air pulse, so I'd suggest thinking about loaders like I mentioned above.
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Unread postAuthor: seudo411 » Sat Nov 03, 2007 12:33 pm

How much are you willing to spend on a gas system.
What i suggest is build a metal coaxial. buy a blow gun to pilot and as far as building your gas system goes follow this for assembly.
co2 tank-> remote line-> on/off mount->
macro line-> regulator->ball valve (or a blow gun)-> Launcher.

This allows you to adjust pressure from o - 300 psi(low pressure)
or on a higher pressure reg 0-500psi.
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Unread postAuthor: blackosprey » Sat Nov 03, 2007 12:43 pm

If I understand what you're saying, that's sort of what I was thinking. But what's an on/off mount? Just a switch that either does or doesn't allow gas through? Same for a macro line, I have no idea what that is.

EDIT: Oh and a slide valve is just something that when you push the button it closes the exhaust path with a "slide" right?
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Unread postAuthor: Ragnarok » Sat Nov 03, 2007 12:55 pm

blackosprey wrote:EDIT: Oh and a slide valve is just something that when you push the button it closes the exhaust path with a "slide" right?

That's a gate valve.

This is a slide/sleeve valve. When pushed forwards, it gives free flow in both directions. When pulled back, it shuts off the input and vents the system port to atmosphere. Very useful for QEVs.
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Unread postAuthor: blackosprey » Sat Nov 03, 2007 1:05 pm

Ok, so let me see if I understand what you're saying. When you're not pulling the trigger, gas from the air source is going in port 1, and up into port 2 and a small chamber. But when you pull the trigger, it cuts off the input into port 1, and allows the gas in the chamber to go through port 2 and out of port 3. Correct?

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Unread postAuthor: Ragnarok » Sat Nov 03, 2007 2:13 pm

Exactly right. By letting air from port 1, the piston/diaphragm (yellow bit) can be forced back by the air on the other side.
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Unread postAuthor: blackosprey » Sat Nov 03, 2007 2:36 pm

Sweet. And I have one more question about the slide valve. What exactly does it mean by venting the system port into the enviroment?
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Unread postAuthor: spanerman » Sat Nov 03, 2007 3:00 pm

it means it dumps the pilot volume to the atmosphere ie, the air around you
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Unread postAuthor: blackosprey » Sat Nov 03, 2007 3:06 pm

Really? Because that would suck, I plan to use a 12g cartridge and I don't want it to be emptied every time I take a shot.
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