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Design in need of input

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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Design in need of input

Unread postAuthor: foilboy » Thu Oct 27, 2011 3:07 pm

As I sat in class today I thought of this design for a air cannon. It's a coax piston cannon with a QEV hooked up so that the chamber side of the QEV is the pilot for the air behind the piston. The exhaust of the QEV (although relatively small in volume) is then sent back into the chamber of the coax. My thoughts with this design would be maximum efficiency from the piston valve (the QEV providing a very rapid exhaust) and added power from the QEV exhausting back into the main coax chamber.

If anyone sees any design flaws or else has any recommendations on improving this design, please chime in.


I have not made this airgun and I do not know if the design is dangerous or not so if you do attempt to build this and are injured by it, I am not responsible
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Unread postAuthor: jrrdw » Thu Oct 27, 2011 3:15 pm

So the tee in your chamber will 1. pressurize you pilot/QEV chamber and the piston wont move or 2. you will vent the main chamber out the QEV or 3. your piston wont move and your chamber will vent out.

I really think 1 is going to be your problem.
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Unread postAuthor: foilboy » Thu Oct 27, 2011 3:20 pm

oooh... I see what you mean. So if there was a check-valve in place at the opening of the tee so that gas could only flow into the coax chamber, that would, in theory, solve issue #1 correct?
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Unread postAuthor: jrrdw » Thu Oct 27, 2011 3:24 pm

Yup.
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Unread postAuthor: Gun Freak » Thu Oct 27, 2011 6:39 pm

Yeah 1, the piston won't seal, and 2, the effective chamber volume is only the pilot volume which by the time it expands and reaches the barrel is nothing.
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Unread postAuthor: Goats spudz » Thu Oct 27, 2011 7:57 pm

like this?
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Unread postAuthor: foilboy » Thu Oct 27, 2011 8:10 pm

Gun Freak, thanks for the input. It's definitely got me thinking.

Goat Spuds, it's similar, I was just hoping to make it coax
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Unread postAuthor: Goats spudz » Thu Oct 27, 2011 8:15 pm

coaxial here we come!
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Unread postAuthor: Gun Freak » Thu Oct 27, 2011 8:18 pm

Goat, that is a regular coax. No need to post a crappy diagram :wink:

Foilboy, I applaud your innovative intent. We have similar minds :)
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Unread postAuthor: MrCrowley » Thu Oct 27, 2011 8:21 pm

Gun Freak wrote:Goat, that is a regular coax. No need to post a crappy diagram :wink:

Think he was just pointing out that the previous diagram he posted could easily be converted to a coaxial as it appeared the OP wasn't aware that it easily could; hence the reply " it's similar, I was just hoping to make it coax" :wink:
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Unread postAuthor: Goats spudz » Thu Oct 27, 2011 8:30 pm

Gun Freak: MSpaint will haunt thee :shock:

really now MAXIMUM efficiency
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Unread postAuthor: MrCrowley » Thu Oct 27, 2011 8:34 pm

@foilboy,
If you did decide to chuck in the check valve, you're going to get such poor flow it wont make much difference. Focus on making a small pilot volume, longer barrel or larger chamber than worry about the wasted air in the pilot :wink:
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Unread postAuthor: foilboy » Thu Oct 27, 2011 8:38 pm

what if I were to add a check valve to the tee into the coax chamber so that air could only go in, and enlarged the piston pilot/QEV chamber area, while making an internal rear bumper that would stop the piston from traveling back too far, but still letting air pass through?

Something like this:
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Unread postAuthor: MrCrowley » Thu Oct 27, 2011 8:41 pm

That would be a horrible design, sorry :wink:

Get rid of this 'pilot exhausting in to the chamber' idea, it's not worth the hassle and I doubt it would show any noticeable increase in performance.

I also fail to see the reason for having the majority of the 'chamber' behind the piston, it would much rather be in front of the piston.

Like I said before, add more barrel or chamber if you have to. Not only is it easier to implement, performance should increase more noticeably. If your chamber is large enough, add barrel length. If you don't want to add more barrel/chamber, up the pressure.

Edit: The reason it is such a bad design (well, one of the reasons) is that the projectile will be half way down range by the time the pilot pressure has fed back in to the chamber.
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Unread postAuthor: mobile chernobyl » Thu Oct 27, 2011 8:43 pm

Needs MOAR Deadspace. :D

Move that piston assembly WAYYYYYY back, and put the check valve in between the first and second Tee's
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